NCDOT Pamlico Wavebreak P1 Mitigation SAV

RK ( MEMORANDUM
8601 Six Forks Road
Forum 1 Suite 700
Raleigh,NC 27615
Phone [phone]
Fax [phone]
www.rkk.com
Date: 11/15/22
From: Kathy Herring
CC: Pete Stafford
Re: B-2500 Submerged Aquatic Vegetation (SAV) Mitigation Project—5 Year Post Construction Project
Summary
Attendees:
Mike Sanderson—NCDOT Environmental Policy Unit Cathy Brittingham- NCDCM
Tyler Stanton—NCDOT EAU BAU Jonathan Howell—NC DCM
Jamie Lancaster—NCDOT EAU Travis Wilson—NC WRC
John Conforti—NCDOT PMU Garcy Ward—NC DWR
Claudia Lee—NCDOT PMU James Harrison—NC DMF
Leilani Paugh—NCDOT EAU Mitigation and Modelling Kyle Barnes- USACE
Paul Williams—NCDOT Division 1 Environmental Officer Twyla Cheatwood—NOAA Fisheries
Mark Fonseca—CSA Ocean Sciences
Kathy Herring—RK&K
Pete Stafford—RK&K
A meeting was held on 10/28/22 for NCDOT to present the end of project summary for the B-2500 Phase I,
Bonner Bridge SAV Mitigation.
After introductions, Mark Fonseca of CSA Ocean Sciences started the presentation with a brief history of
the project followed by the general theory and application of the wavebreak. He then presented results
and conclusions and opened the meeting to discussion.
Project purpose
• Replacement of the Bonner Bridge would have 2.66 ac of SAV Impact, 1.38 ac of suitable habitat
was returned, or unshaded, by the removal of the old bridge resulting in 1.28 ac of SAV requiring
mitigation

Project Concept
• Reduce the wave energy on patchy seagrass beds to allow them to expand and coalesce by
constructing a wavebreak
History and Timeline
• 2015 CSA teamed with SEPI Engineering for design
• 2015-2016 applied for and received permits for the wavebreak structure,
• May 2016—seagrass was relocated from the construction site
• Casting of wavebreak units began October 2016
• Construction occurred from November 2016 to January 2017
Theory application
Reduce wave energy on open water, patchy SAV beds to facilitate bed coalescence and increase SAV cover
per unit area seafloor
• The theory was based on work published in 1998 that developed a model relating seagrass landscape
patterns to wave energy and currents
o Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near
Beaufort, NC, USA. Marine Ecology Progress Series 171:109-121.
■ https://www.int-res.com/articles/meps/171/m171p109.pdf
o Uhrin and Turner 2018. Physical drivers of seagrass spatial configuration:the role of thresholds
o Based on a NOAA wave exposure model (WEMo)
• Revised WEMo to provide quantitative estimates of wave energy
• Wavebreak location was determined by collecting extensive bathymetry data to inform the wave
exposure model to forecast change in SAV cover.
• The East/west orientation model run produced the greatest change in SAV acreage
Site Preparation
• Examined existing SAV distribution from available imagery and ground inspection
• Relocated SAV out of structure footprint and construction corridor
• Collected baseline data for Sediment Digital Elevation Model (DEM)with a USV
Monitoring—conducted 2x/year for 1st two years then annual for next two years
• Sediment Elevation-measured monthly for 1st year,then reduced
• Wave Energy
• SAV change in cover over time from aerial surveys
• Essential Fish Habitat—colonization by sessile fauna
o Photos of fixed points compared over time
Results
• Sediment Elevation—Near field
• A scour pit developed underneath wall
• A sand apron formed limiting seagrass growth in that area temporarily
• After a year the sand pit stabilized at 2-3 feet deep along the wall
• The shoal remained stable
• Sediment Elevation—Far field

• Both shoaling and erosion occurred between 2016 and 2021
• No visually apparent spatial pattern of shoal-wide loss/gain was attributable to wavebreak
• Waves
• Top 5%of wave events drive seagrass landscape response
• Seasonal differences
• North had 5 times more larger waves than the South side
• Average, minimum,and maximum wave heights were slightly larger from the south
• East-west orientation gave wave protection to SAV on both north and south sides
• SAV
• Area separated into Zones based on % reduction in wave energy
• No response to hurricanes during study
• Starting in 2021 growth in all zones increased including some of reference areas, however,
the gains did not occur as much in the reference areas.
• August 2020 to August 2021—substantial gain in high reduction zones just south of wall
• Looking at 2018 versus 2021,we see a general increase in grass up and down the length of
the shoal
• Patch migration occurred, but there was a general seagrass gain in coverage
• After a long pause, presumably due to the sediment apron,SAV coalescence initiated in the
predicted location
■ Possibility of a shoal-wide cascade effect
• Increase in Ruppia indicates a more quiescent environment
• Essential Fish Habitat
• In the lower zones of the structure that were always inundated,we see nearly 100%
colonization by barnacles and oysters
• Higher zones are a barnacle algae mix
• Steady colonization since construction
• Many fish under and around the wall 1
Conclusions
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• SAV coverag changes cross disturbance gradients
• Manipulation of gradient changes'n SAV coverage
• Reefmaker method with suspended wavebreak structure:
o Supported new, persistent seagrass cover as per past studies—Ruppia indicator
o Provided substantial additional EFH service 7)
• SAV acreage gained > mitigation requirements of 1.28 acres b 0-1— of- (lI1-�3, 0
• Potential landscape-scale cascade of SAV cover
• Forecast response consistent with model
Discussion
Jimmie Harrison asked if SAV coverage increases were based on the SAV species recorded.
• Response—no,the only area in which we really monitored changes in SAV was in the relocated
areas just south of the wall. Otherwise,we just focused on cover.
Cathy Brittingham asked if there was still any intent to try and fill the scour pit with non-erodible material.
• Response—no, not now that the scour pit is stable,and the grass has established itself onto the
"sand apron" area.

Cathy also asked if it is NCDOT's intent to close out the monitoring requirements under the CAMA permit
for the SAV mitigation and then transitioning to long term maintenance of the wave break structure or
continuing the monitoring?
• Response—Kathy Herring stated that it is the intent of the NCDOT to close out the monitoring
requirements for the CAMA permit for B-2500 Phase I, Bonner Bridge Replacement, but to continue
monitoring the wavebreak structure at least during the growing season through the Rodanthe
Bridge monitoring period.
Garcy Ward asked if the wall would require maintenance and what is the expected lifespan of the wall?
• Response—Maintenance of the wall will be conducted as needed by the NCDOT.The BAU is
currently conducting periodic checks to make sure the safety lights are working. The project was
designed and built to FHWA standards including the materials used. So, it would be expected to
have a lifespan of decades. Kathy also responded that as long as the NCDOT owns the structure
they would be responsible for any maintenance it requires.
After the presentation Kathy Herring explained that the additional reports distributed to the group were
the results of the monitoring that was conducted under and around the new Basnight Bridge and the old
Bonner Bridge. These reports indicate that the seagrass and marsh where the bridge was removed is
recovering. ` �— 7,eok
Meeting was adjourned.

Brittingham, Cathy
Subject: B-2500 SAV Mitigation Project— 5 Year Post Construction Project Summary
Location: DOT CCA Technical Services Conf. Room Col. C11 (Cap 30)
Start: Fri 10/28/2022 9:00 AM i
End: Fri 10/28/2022 12:00 PM 1 A /C.O rn� Vie
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Recurrence: (none) ---\'\ \QN
Meeting Status: Accepted dr _a 5r0 S7v 5)rn rna
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Organizer: DOT INTERAGENCY MEETING CALENDAR �P a
Required Attendees: Sanderson, Mike;Wilson, Travis W.; Cox, Marissa R; Matthews, Monte K CIV USARMY
CESAW (US <[e-mail]>; Lancaster,Jamie J; Conforti, John G;
Harrison, James A;Ward, Garcy; Kathy Herring; Pete Stafford; Fonseca, Mark
<[e-mail]>; Lee, Claudia W; Brittingham, Cathy; Chapman, Amy;
Daisey, Greg; Deaton, Anne; Paugh, Leilani Y; Rivenbark, Chris; Williams, Paul C; Stanton,
Tyler P;[e-mail]; Bar Kyle W CIV USARMY CESAW (US)
<[e-mail]> (`d J kk �an�Pr e�; acre_ SAV
Optional Attendees: Howell,Jonathan R—e ��--_ ad a _
Resources: DOT CCA Technical Services Conf. Room Col. C11 (Cap 30) E'S
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All,
Summer 2021 marked the end of the B-2500 Bonner Bridge Replacement Project SAV Mitigation monitoring period. As
per the CAMA Permit Major Modification, issued on 12/15/15, permit condition No. 21 that : "The permittee shall
conduct an annual meeting with DCM and other appropriate resource agencies to discuss and review the annual
monitoring reports and monitoring methodology for a minimum of five years after mitigation site construction." I have
attached the B-2500 SAV Year 5 Annual Report for your re \3—
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All 5 annual reports and the UAV monitoring reports can be downloaded from here: -' 5e-Q—
https://xfer.services.ncdot.gov/pdea/B2500/UAV%20Reports/
and here: A\‘-e_aSt \' e S
https://xferservices.ncdot.gov/odea/B2500/Wavebreak%20Reports/
Please call Kathy Herring at(919) 971-4367 if you have any questions. 7 jtc,,),e,-1-13-
Microsoft Teams meeting
Join on your computer, mobile app or room device
Click here to join the meeting
Meeting ID: 213 028 840 039
Passcode: p8Vbzg
Download Teams I Join on the web
1

xfer.services.ncdot.gov - /pdea/B2500/UAV Reports/
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Prepared for: Prepared by:
Environmental Analysis Unit CSA Ocean Sciences Inc.
North Carolina Department of Transportation 8502 SW Kansas Avenue
1598 Mail Service Center Stuart, Florida 34997
Raleigh, North Carolina 27699-1598 /'....' L7-1
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CSA
CSA Ocean Sciences Inc.
B-2500 Bonner Bridge Seagrass Mitigation Site
Year 5 Annual Survey and Project Final Report - 2021
DOCUMENT NO. NCDOT-FL-22-1830-2845-21-REP-01-FIN
Internal review process
Version Date Description Prepared by: Reviewed by: Approved by:
INT-01 01/10/2022 Initial draft for M.Fonseca E. Hodel M. Fonseca
science review
INT-02 01/18/2022 TE review M. Fonseca K. Metzger M. Fonseca
Client deliverable
Version Date Description Project Manager Approval
01 01/21/2022 Client deliverable E. Hodel
02 03/22/2022 Final client E. Hodel
deliverable
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

Table of Contents
Page
List of Tables v
List of Figures vi
List of Photos vii
1 Introduction 1
2 Background 3
2.1 Project Concept:Goals and Drivers of SAV Pattern (Waves,Currents, Bioturbation) 3
2.2 Project History 5
2.3 Site Selection and Preliminary Wave Energy and SAV Response Modeling 5
3 Monitoring Metrics 9
3.1 Bioturbation Study 9
3.2 Wavebreak Structural Assessment 10
3.3 Wave Energy Monitoring 10
3.4 Sediment Elevation 10
3.5 Success of Relocated SAV 12
3.6 Wavebreak Epibiota—Essential Fish Habitat 13
3.7 SAV Response 13
4 Results and Discussion 14
4.1 Bioturbation Study 14
4.2 Wavebreak Structural Assessment 15
4.3 Wave Energy Monitoring 15
4.4 Sediment Elevation 17
4.5 Success of Relocated SAV 22
4.6 Wavebreak Epibiota EFH assessment 23
�\n 4.7 SAV Response 26
4.7.1 Monthly Aerial Surveys 26
4.7.2 Change Analysis from Aerial Surveys 28
5 Conclusions and Next Steps 32
5.1 Did it Work? 32
5.2 Lessons Learned 36
5.3 Future STEPS and Applications 36
6 References 38
Appendices 41
Appendix 1 Bonner Bridge Seagrass Mitigation Project(State Project 32635.1.3;TIP B-2500)
Task B(Site Verification) 1-1
Appendix 2 Bonner Bridge Seagrass Mitigation Project(State Project 32635.1.3;TIP
B-2500) 2-1
Appendix 3 Bonner Bridge Seagrass Mitigation Project(State Project 32635.1.3;TIP B-2500) 3-1
Appendix 4 SEPI Engineering and Construction Inc., Wavebreak Site Layout and Wavebreak
Structure Schematics 4-1
NCDOT-FL-22-1830-2845-21-REP-01-FIN iii

Table of Contents
(Continued)
Page
Appendix 5 Bonner Bridge Mitigation Structure Annual Inspection 2020 Pamlico Sound,
Oregon Inlet (B-2500) Bridge Replacement Project Dare County, NC. September-
October 2020 5-1
Appendix 6 Change in sediment elevation among the replicate rods in each of the wave
energy reduction strata among for all comparisons of Survey 1 with subsequent
Surveys 6-1
Appendix 7 Representative Photos of Seagrasses within the Planting and Reference areas
throughout the Monitoring Program 7-1
Appendix 8 Results of Relocated SAV versus Reference Areas 8-1
Appendix 9 Results of Water Level Observations and Epibiota Surveys, 2017-2021 9-1
Appendix 10 Representative Photographs of Colonized Substrate and Sessile and Motile
Fauna from the July 2021 Survey 10-1
Cover Photo Credits:Left-hand, aerial image of wavebreak:Pete Stafford, RK&K Engineering(July 2021);
right-hand image by Erin Hodel CSA Ocean Sciences Inc. (July 2021).
NCDOT-FL-22-1830-2845-21-REP-01-FIN iv

1
List of Tables
Table Page
1 Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation
Site 2
2 Years and months during which aerial overflights were performed for SAV mapping
around the wavebreak 13
3 Summary statistics of the top 5%of wave heights measured at the two sensor
stations on the north and south sides of the wavebreak excluding 2020 to 2021 data 16
4 Summary of SAV acreage change analysis within the model forecast high wave
energy reduction zone (>66% reduction) and the medium wave energy reduction
zone (33 to 66%reduction) among the peak growing season (August), by year 31
NCDOT-FL-22-1830-2845-21-REP-01-FIN v

List of Figures
Figure Page
1 Collage of two aerial images from coastal North Carolina showing development of
submerged aquatic vegetation (SAV) in the lee of dredge material islands 4
2 Relationship of submerged aquatic vegetation (SAV) percent cover of the seafloor to
representative wave energy(Joules m-1 wave crest) 5
3 Schematic of individual Atlantic Reefmaker wave attenuation unit; 101 of these
units installed conterminously compose the wavebreak structure 7
4 Sand apron south of the wavebreak visually outlined from aerial imagery collected
on 18 April 2018 12
5 Difference in hourly significant wave heights(m) between the north and south side
of the wavebreak for January 2017 through July 2021 16
6 Digital elevation model constructed from a survey in 2016 by an Autonomous
Surface Vehicle at the Bonner Bridge Seagrass Mitigation Site prior to construction
of the wavebreak(ultimate location of wavebreak shown) 18
7 Digital elevation model constructed in 2021 from a survey by an Autonomous
Surface Vehicle at the Bonner Bridge Seagrass Mitigation Site five years
post-construction of the wavebreak 19
8 Differences in elevation among the two digital elevation models from 2016 and
2021 20
9 a) Percent cover of total epibiota for concrete portions of the wavebreak disks as of
July 2021 25
10 Percent cover of total submerged aquatic vegetation (SAV) by aerial survey month in
August 2018 through December 2020 for each of the wave energy reduction zones 27
11 Change in percent cover of submerged aquatic vegetation (SAV)surrounding the
wavebreak for the months of August 2018 vs.August 2021 29
12 Change in percent cover of submerged aquatic vegetation (SAV)surrounding the
wavebreak for the months of August 2020 vs.August 2021 30
13 2015 image of wavebreak location showing patchy submerged aquatic vegetation in
the area surrounding the wavebreak 33
14 August 2021 image of wavebreak survey area showing submerged aquatic
vegetation in the area surrounding the wavebreak 34
NCDOT-FL-22-1830-2845-21-REP-01-FIN vi

J
List of Photos
Photo Page
1 The Marc Basnight Bridge (foreground) and previous, Bonner Bridge (just above the
Basnight Bridge),spanning over Oregon Inlet in the Outer Banks, North Carolina 1
2 a) Installation of the wavebreak structure in January 2017 showing a crane lifting a
partial stack of concrete disks for placement over a piling 8
3 Oyster colonization on rocks in a middle disk elevation (July 2021) 24
4 Aerial image showing fish aggregation surrounding the eastern half of the
wavebreak(250 feet length)on 02 October 2021 24
NCDOT-FL-22-1830-2845-21-REP-01-FIN vii

1 Introduction
The North Carolina Department of Transportation (NCDOT)contracted CSA Ocean Sciences Inc. (CSA) in
2012 (Contract No. 6300032017)to conduct in-kind experimental submerged aquatic vegetation (SAV)
(here mixed Halodule wrightii, Ruppia maritima,Zostera marina) mitigation of 1.28 acres (0.52 hectares)
to compensate for SAV losses anticipated to occur during construction of the Marc Basnight Bridge,
which replaced the Herbert C. Bonner Bridge over Oregon Inlet, North Carolina (Photo 1).The Bridge
provides the only road connection for Hatteras Island to the mainland in Dare County, North Carolina.
Construction was completed and opened to traffic in February 20191.
Based on previous published research in North Carolina (Fonseca et al., 1998, Fonseca et al., 2000,
Kelly et al., 2001, Fonseca et al.,2002) CSA conceptualized creating a wavebreak structure to generate
new SAV cover by attenuating wave energy in patchy SAV habitat thereby creating additional, persistent
SAV acreage through patch expansion and recruitment.This subsequent increase in SAV acreage was
expected to meet NCDOT's SAV mitigation requirements while enhancing ecosystem services including
Essential Fish Habitat (EFH)for the surrounding area.
•
Photo 1. The Marc Basnight Bridge (foreground)and previous, Bonner Bridge(just above the Basnight
Bridge),spanning over Oregon Inlet in the Outer Banks, North Carolina. Image with
permission from Carolina Designs, https://www.carolinadesigns.com/.
In 2012, NCDOT contracted CSA to lead the Bonner Bridge Seagrass2 Mitigation Site Project associated
with Project B-2500, replacement of the Bonner Bridge. Following a pause in activities due to project
litigation, pre-construction surveys were performed from April 2015 to June 2016. Construction of the
1 https://www.ncdot.gov/news/press-releases/Pages/2019/2019-04-02-marc-basnight-bridge-ribbon-cutting.aspx.
Last accessed 18 March 2022.
2 Early project documents typically refer to"seagrass"instead of"submerged aquatic vegetation"or SAV. Later in
the project the more general term SAV was adopted to reflect the broad utility of the project basis.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 1

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wavebreak was completed in January 2017 and entailed installation of 101 conterminous Atlantic
bo‘)1\
Reefmaker(AR) units in a chevron pattern oriented due north.A baseline monitoring survey(CSA, 2017)
occurred immediately after construction,followed by five years of post-construction monitoring:three
years of bi-annual surveys followed by two years of annual surveys, concluding in 2021. Biannual and
annual monitoring included wave energy monitoring,sediment elevation surveys,success of relocated
SAV, and wavebreak epibiota assessments.Table 1 summarizes the project's milestone activities and
monitoring events. In 2021,the Year 5 Annual Survey was conducted from 19 to 22 July,followed by a
bathymetric survey from 24 to 27 August.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak.
Task Date Survey Status
Number
Pre-construction
Site Selection Survey April 2015 n/a Complete
Seagrass Transplantation and Bioturbation Experiment May 2016 1 Complete
Initiation
Sediment Digital Elevation Survey(ASV) June 2016 n/a Complete
Construction
18 Nov.2016 to 18 Jan.
Wavebreak Installation 2017 n/a Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan.2017 2 Complete
Year 1 Biannual Monitoring Survey October 2017 3 Complete
Year 2 Annual Monitoring Survey May 2018 4 _ Complete
Year 2 Biannual Monitoring Survey October 2018 5 Complete
Year 3 Annual Monitoring Survey May 2019 6 Complete
Year 3 Biannual Monitoring Survey October 2019 7 Complete
Year 4 Annual Monitoring Survey July-August 2020 8 Complete
Year 5 Annual Monitoring Survey+Sediment Digital July August 2021 9 Complete
Elevation Survey(ASV)(Final Project Report)
ASV=autonomous surface vehicle.n/a=not applicable.
This report serves as the Year 5 Annual Report and the Project Final Report for the project. Per
communication with NCDOT staff and RK&K Engineering (RK&K), it takes a different form than previous
reports. Here,the report is structured to provide the reader with a succinct and more holistic view of
the project which was initiated in 2012. Details of methods and discrete findings are left to Appendices
or by reference to numerous previous reports (e.g., CSA, 2017, 2018a,b,2019, 2020). New findings that
have not shown meaningful change since earlier data reports are relegated primarily to Appendices.The
emphasis here was to elucidate trends and guide the reader to conclusions regarding this near
decade-long experimental effort and on to considerations of future applications.
To provide a more complete picture of changes in SAV and sediment dynamics associated with the
wavebreak,some findings from other associated studies conducted by CSA under contract to RK&K and
studies conducted by subcontractors to CSA are integrated in this report. Specifically,these studies
provided data on SAV abundance from aerial reconnaissance,sediment elevation surveys, and
wavebreak structural assessments.
NCDOT-FL-22-1830-2845-21-REP-0I-FIN 2

2 Background
2.1 PROJECT CONCEPT:GOALS AND DRIVERS OF SAV PATTERN
(WAVES, CURRENTS, BIOTURBATION)
As early as 2010, discussions between science staff(then at NOAA and later at CSA) and the
North Carolina Department of Transportation (NCDOT)were had regarding options for promoting SAV
coverage as mitigation arising from anticipated impacts to SAV during the upcoming replacement of the
Bonner Bridge at Oregon Inlet, North Carolina. Historically, SAV mitigation has occurred at sites where
human impacts reduced or eliminated SAV and those impacts ceased, creating an opportunity for
restoration of the impacted site (Fonseca et al., 1998). However, early field visits by both science and
regulatory staff found little anthropogenically impacted SAV habitat in the vicinity of the Bonner Bridge
that could serve as a mitigative alternative. Rather than consider out-of-kind mitigation, an alternative,
experimental approach for creating new, sustainable SAV acreage was considered to generate the
mitigation acreage needed for the Bonner Bridge replacement project.
Many examples exist of SAV increasing in abundance in the lee of structures that reduce wind waves.
Over recent decades, creation of dredged material disposal islands along the NC coast has provided
examples of discontinuous or patchy SAV landscapes shifting to more continuous cover of the seafloor in
the lee of those islands (Fonseca et al., 2002, Figure 13). Similar instances in the southeast and Gulf
Coast can also be found of SAV beds developing in the lee of wave-reducing structures. The
commonality of this phenomenon prompted the Tampa Bay Estuary Program (Cross, 2013)to construct
several, 200 ft-long shore-parallel structures to replace the effect of eroded longshore sand bars and
promote SAV expansion in their lee. The widespread observation of SAV response to wave energy was
sufficiently compelling to propose the creation of a wave attenuation structure (wavebreak) in patchy
SAV beds on shoals near the Bonner Bridge to promote SAV patch coalescence, propagule recruitment,
and new, permanent SAV acreage on the seafloor.
3 In the electronic version of this report,the reader is encouraged to zoom into figures and photos to observe more
clearly some of the various finer-scale features.
NCDOT-FL-22-1830-2845-21-REP-0I-FIN 3

Dredge Material Islands inside Oregon Inlet
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Approximate Location of Wavebreak
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Dredge Material Island at Garden's Inlet ;`'¢
Figure 1. Collage of two aerial images from coastal North Carolina showing development of
submerged aquatic vegetation (SAV) in the lee of dredge material islands.The black and
white image in the lower left is from 2012 and shows the island at the end of Barden's Inlet.
Increased density of SAV is seen on the southwest side and in the lee of a long northeast
fetch. In the larger color image mosaic(circa 2012)of the waters west of Oregon Inlet,
several dredge material islands with SAV concentrations in their lee from dominant
northeast winds and tidal currents from the inlet are evident.The approximate location of
the wavebreak is also shown (not to scale).Approximate image width of inset is 0.6 mile and
of color mosaic is 5 miles.
Observations of SAV coalescence in response to wave energy reduction led to research on the
relationship of wind waves and tidal currents to SAV landscapes (Fonseca and Bell, 1998, Uhrin and
Turner, 2018)and a generalized model of SAV percent cover of the seafloor in relation to wind wave
energy(Figure 2; Fonseca and Bell, 1998). In those studies, increased wind wave exposure at a site was
associated with a pattern of smaller and fewer SAV patches than at sites with less wave energy.Very low
wave energy sites were typically composed of extensive SAV beds with unbroken cover.Thus,the
concept of wave energy reduction through creation of a wavebreak in persistently patchy SAV habitat
(where that patchiness was likely due to chronic wave exposure)to promote new SAV acreage was
harnessed as a mitigation strategy. Reduction in wave energy on patchy SAV in the lee of the wavebreak
would then promote new, persistent SAV acreage through patch coalescence and propagule
recruitment, moving the wave environment of those patchy SAV beds upslope on the regression line in
Figure 2 to a new state of landscape cover.The expectation was that promotion of SAV coalescence
would begin to occur immediately after construction of the wavebreak, primarily by rhizome extension
from existing SAV.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 4

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en BEEEMBEE2--z==.13—MEEEMILUzzzell
0 200 400 600 800 1000 1200 1400 1600 1800 2000
REPRESENTATIVE WAVE ENERGY(Joules m l wave creast)
Figure 2. Relationship of submerged aquatic vegetation (SAV) percent cover of the seafloor to
representative wave energy(Joules m-1 wave crest). Recomputed from Fonseca and
Bell (1998).
2.2 PROJECT HISTORY
From 2012 to 2017,the project was in a planning phase,with a suspension of activities during a lawsuit
against the project between June 2013 and March 2015(a history of the entire Bonner Bridge project
can be found here4). Starting again in March 2015,the project was revised from use of an engineered
but temporary wooden wavebreak structure modeled after Broome et al. (1992)to an experimental
wavebreak utilizing AR units that among other attributes,created a quasi-permanent structure to
ensure a long-lasting increase in SAV acreage.This shift in regulatory perspective from that of a
temporary structure to consideration of a permanent structure reflected a desire on the part of NCDOT
to explore experimental alternatives to SAV mitigation in anticipation of upcoming coastal construction
needs.An internal review of alternative structures was performed (Appendix 1) and the functionality of
the proposed wavebreak(permanence, minimum physical footprint, met federal highway standards of
construction, and the design being signed and professionally sealed)was seen as superior to other
configu rations.
2.3 SITE SELECTION AND PRELIMINARY WAVE ENERGY AND SAV RESPONSE MODELING
Selection of the location for the wavebreak was informed first by viewing historical aerial imagery of
shoals with patchy SAV within the vicinity of Bonner Bridge (approximately 8-16-km [5-10-mile]
radius of Oregon Inlet). Shallow shoals with persistently (over at least a decade) patchy SAV cover
were identified from the imagery. Site visits to these shoals to verify water depth and SAV status
occurred at various times from 2013 to 2016 and four sites were initially considered (Appendix 2).Two
sites were given higher priority based on the patchiness of SAV and low overall percent cover, meaning
there was substantial seafloor available for SAV expansion.A detailed bathymetric survey was
conducted in 2012 which covered 80 km2 with approximately 3 0 km of survey lines,with a focus on
site#2 and other sites with higher SA\ cover(Appendix 2).The thymetry survey confirmed that
30--% 5c ; m\ . 1Z vh\\eS
https://www.ncdot.gov[projects/bonner-bridge/Pages/project-historv.aspx Last accessed 18 March 2022.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 5

(1 had shallower and more consistent bathymetry as compared to other sites.The low SAV cover
1%cupported by an on-site survey using Braun-Blanquet [1972] quadrats and line intercept
surements of SAV cover along transects;Appendix 2),the visually apparent consistency of that
cover from historical aerial imagery,and wave energy modeling(below),was the basis for selection of
site#2 as the experimental site.
Wave modeling was then undertaken using WEMo(Malhotra and Fonseca, 2007)to quantify the degree
of wave attenuation expected for various orientations of various length wavebreak5 structures on
site#2 (Appendix 3).Tide-corrected bathymetry data from the 2012 survey were embedded in the
larger extent (NOAA Coastal Relief Model') bathymetric data used for the modeling to provide
improved, near-field (near to the wavebreak site)wave energy forecasts.The relationship of wave
energy(J m-1 wave crest)derived from WEMo(versus an index previously used in Fonseca and
Bell 1998')and SAV percent cover was recalculated (Figure 2) producing a stronger regression model
(r2 of original =0.45;the recomputed model r2=0.75 [Figure 2]). WEMo results from simulated
configurations of the wavebreak orientation (Appendix 3)confirmed for the regional wind field covering
this area,an east-west orientation of the wavebreak could produce the greatest change in SAV cover as
this orientation produced the largest wave energy reduction shadow.The difference in SAV cover arising
from the forecast reduction in wave energy was derived by comparing regression-forecast SAV
abundance(Figure 2) per unit area of seafloor both before and after simulation of the wavebreak.The
forecast difference (gain) in SAV per unit area as the result of the wave energy reduction was summed
across the wave shadow area to yield a forecast change in SAV acreage.
Thus,the configuration and location of the structure was based on a combination of considerations
including review of aerial imagery over time,site visits, and wave modeling of wavebreak configuration
and orientation. Based on a regulatory position of not granting mitigation credit for any new SAV
beyond the 1.28-acre target,the length of the simulated wavebreak was varied and the resultant new
SAV acreage computed. From the relationship of simulated wavebreak length in the east-west
orientation to forecast, new SAV acreage, a wavebreak length of 500 linear feet was selected to create
the target level of 1.28 acres of new SAV seafloor coverage(CSA, 2018a,Appendix 3).A chevron shape
of the wavebreak was selected to provide additional deflection of waves from the north which was seen
in the WEMo modeling to be the direction of extreme wind wave events,while still reducing wave
energy for SAV on the north side of the wavebreak from persistent southerly winds.
A description of the final wavebreak design can be found in Appendix 4.The wavebreak is composed of
101 pilings with four, 1.2 x 1.2 m (4 x 4 ft)concrete disks per piling(Figure 3 and Appendix 4). In January
2017 the construction of the wavebreak(Photo 2a,b)was completed. Following construction,five years
of monitoring followed, described in this final,Year 5 Annual Report.
'This length was that which was forecast as necessary to generate the target SAV acreage.Additional SAV acreage
beyond that of the target acreage was at the time not viewed by regulatory agencies as available for credit to
future projects so a larger wavebreak was not justified.
6 https://www.ngdc.noaa.gov/mgg/coastal/crm.html Last accessed 18 March 2022.
'As of 1998 the WEMo model only utilized a relative exposure index and had not yet incorporated a quantitative
measurement of wave energy as used in this study.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 6

•
V Water surface
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Figure 3. Schematic of individual Atlantic Reefmaker wave attenuation unit; 101 of these units installed conterminously compose the
wavebreak structure. Reproduced from SEPI Engineering Inc. drawing. The water surface is shown at a typical high tide.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 7

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Photo 2. a) Installation of the wavebreak structure in January 2017 showing a crane lifting a partial
stack of concrete disks for placement over a piling. Note the shallow water depth with
workers standing nearby. b) Completed wavebreak structure in January 2017 looking to the
west at high tide from approximately AR unit 40.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 8

3 Monitoring Metrics
Seven types of monitoring were undertaken to understand the effect of the wavebreak:
1. Bioturbation study(potential role in preventing SAV coalescence);
2. Wavebreak structural assessment (physical integrity and prognosis for long term);
3. Near-continuous wave energy monitoring;
4. Sediment elevation (what was the effect of the structure on the surrounding shoal environment);
o Far-field (199.3 ac [80.6 ha] acres of the shoal surrounding the wavebreak);
• Digital Elevation Model (DEM);and
• Rods
o Near-field (150-ft [45.7-m]transects originating at the wavebreak)
5. Success of relocated SAV;
6. Wavebreak epibiota EFH assessment; and
7. SAV long term response (focusing on generation of new, persistent SAV acreage);
o Aerial imaging summary(monthly);
o Change analysis
3.1 BIOTURBATION STUDY
A bioturbation study was undertaken to understand the relative influence of biological disturbance
versus wind wave energy on SAV bed patchiness.To evaluate the influence of biological disturbance on
SAV patches at the site(sensu Townsend and Fonseca, 1998), CSA installed a bioturbation exclusion
experiment in May 2016. Forty locations were randomly selected from within four wave energy
reduction strata (10 locations per strata)as defined by the forecast wave reduction pattern following
wavebreak placement(high wave energy reduction=>66%; moderate reduction=33 to 66%, low
reduction=5 to 33%, and ambient or reference=<5% reduction) (CSA, 2017, 2018a).The nearest
isolated SAV patch to that random location was then selected for application of the experimental
treatment.At the center of all 40 patches, a 2.4-meter(8-foot) long stainless-steel rod was driven into
the sediment until only 3 to 10 cm (1 to 4 in) remained above the sediment and the elevation of the rod
above the sediment was recorded. For each stratum,five randomly selected patches were assigned two
wire remesh panels (wire remesh8 panels 1.07 m x 2.13 m [42 in x 84 in],with 0.106 m x 0.1.06 m
[4 in x 4 in] mesh size)to exclude bioturbating sting rays and five were left un-protected.At each of two
randomly selected cardinal directions per patch,the distance from the center rod to the edge of the SAV
patch was measured. For patches receiving mesh,each of the two cardinal directions received a wire
mesh.The longest length of the mesh was positioned parallel to the patch edge approximately 1/3 on
SAV and 2/3 on sand to allow room for SAV expansion into the remesh. Change in the distance from the
center rod to the patch margin was to be recorded over time.The statistical approach for this
experiment was to be a repeated measures two-way analysis of variance with wave energy and patch
protection as main effects.
8 Wire reinforcing mesh used to strengthen concrete slabs.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 9

3.2 WAVEBREAK STRUCTURAL ASSESSMENT
Wavebreak structural assessments were made visually during site visits by both CSA staff and other
contractors working for NCDOT.Annual inspection surveys were conducted from 2018 to 2020 regarding
the physical integrity of the AR structure and their maintenance of the vertical position of concrete disks
on the pilings (subsidence) (SEPI,2019, 2020, 2021).
3.3 WAVE ENERGY MONITORING
Long Term Wave Regime: Long-term, nearly continuous wave energy regime monitoring stations were
installed at the Bonner Bridge Seagrass Mitigation Site to record wave characteristics. In January 2017,
two pressure sensors (RBRvirtuoso models)were each deployed at stationary locations 25 m (82 ft)
north and south of the wavebreak structure(CSA, 2017, 2018a, 2019, 2020). Pressure sensors were
mounted in a locked casing approximately 15 cm (6 in) above the substrate on a solid base,
concrete-filled pillar set 0.91 m (3 ft)into the seafloor. Pressure sensors were set to record bursts of
pressure data every 30 minutes at a sampling rate of 4 Hz for 128 seconds.
WEMo model validation: Model validation was repeatedly attempted through opportunistic sampling
around the wavebreak structure. During times of onsite monitoring surveys, an RBR sensor was
systematically but temporarily relocated across the site in a grid pattern (CSA, 2020)to obtain a spatial
assessment of predicted (WEMo computation to follow based on water depth and wind conditi ns of
the survey date)versus observed wave heights from the mobile sensor. oo� • \
3.4 SEDIMENT ELEVATION
The influence of the wavebreak on the surrounding seafloor sediment elevation was of particular
interest as any shoaling or erosion could influence SAV abundance and distribution.Shoaling could raise
the seafloor above the limits of SAV exposure at low tide and conversely,erosion could result in
wholesale removal of established SAV and prevent subsequent recolonization. Both far-field (beyond
150 ft [45.7-m]from the wavebreak)and near-field (within 150 ft [45.7-m] of the wavebreak)surveys
were performed at various times to detect any baseline shifts in the flood tide delta shoal formation
itself(far-field)and those in close proximity to the wavebreak and more likely responding to the
presence of the structure itself(near-field).
Far field—Digital Elevation Model: In June 2016,CSA used a 5m Autonomous Surface Vehicle (ASV)to
develop a sediment DEM to document changes in shoal elevation associated with the wavebreak
installation (CSA, 2017).The ASV was pre-programmed to run a pre-selected geographic grid at 50-m
(164-ft) line spacing which encompassed the entire site. Bathymetry data was collected using dual
frequency,single beam sonar at a rate of 220 to 224 kHz. A Trimble Real Time Kinematic system (RTK)
was mounted on the ASV to integrate real time navigation while the ASV ran the pre-programmed
grid lines(speed of approximately 9 kph [5.7 mph]).The RTK had a horizontal and vertical accuracy of
2 cm (±0.787 in)and real-time tidal corrections were applied to accurately determine water levels
across the site.This survey was repeated in July 2021 using a Sea Robotics (SR) M1.8 Surveyor ASV,
following the same grid lines as in 2016. Here the ASV collected bathymetry with an EchoLogger
EU D032 dual-frequency(30/200 kHz) single beam echosounder, again normalized with real-time tidal
corrections.This survey provided the most spatially comprehensive assessment of bathymetric change
in the larger shoal structure on which the wavebreak is located.A before (pre-wavebreak construction)
and after comparison (June 2016 vs.August 2021)was performed to quantify any spatial changes in
bathymetry over this time. 1
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NCDOT-FL-22-1830-2845-21-REP-01-FIN oC\-0\ cc cb 5 f n �� � 6 o\-\ ck\\.C510

Far field—Elevation Rods:This method was utilized during all monitoring surveys and included direct
measurement of the height of the center rod above the seafloor/substrate at each of the 40 stations
originally established for the bioturbation experiment(CSA, 2017,2018a, 2019, 2020).At each station,
the rod height above the seafloor/substrate was measured using a meter stick fastened to a piece of
wood (24 cm x 5 cm x 5 cm [18 in x 2 in x 2 in]).The 0-mark on the meter stick was attached to the
center of the wood piece creating an inverted "T" shape.The wood was laid flush against the seafloor to
provide more surface area to avoid the ruler sinking into the substrate.The meter stick was placed next
to the rod to obtain the measurement of the rod height above the substrate. In addition to the
40 center rods,four additional sediment rods (one per wave energy regime)were installed in sandy
substrate and rod height above the substrate was measured for each. Change in sediment elevation
among surveys and across the wave energy strata was computed for each combination of survey times.
The differences in change in sediment elevation among strata for each comparison of survey times were
compared in a 1-way ANOVA using PROC GLM in SAS 9.4 after In+10 transformation (to avoid negative
numbers and address any non-normality of the data). This survey did not have the spatial resolution of
the ASV-based survey but was performed with greater frequency.
Near field—Sediment Elevation Transects: In June 2017,a near-field method of sediment elevation
assessment was initiated by NCDOT. SEPI Engineering Inc. (SEPI)was contracted by NCDOT to conduct
high density, near-field sediment elevation measures in the vicinity of the wavebreak. North-south
oriented transects were established at five equally spaced locations centered on the wavebreak
(CSA, 2018a, 2019, 2020) and sediment elevations corrected to mean lower low water(MLLW)surveyed
in June 2017,September 2017,and then monthly starting January 2018;reported here through June of
2018).Transects were placed on both the north and south side of the wavebreak. In 2017,elevations at
distances of 0(at the edge of the wavebreak),5, 10,20, 50, 75, and 100 ft(1.5, 3.0, 6.1, 15.2, 22.9,
30.5 m)were recorded. In January 2018 that changed to increments of 5 feet out to 50 ft and then at
75 and 100 ft to improve sensitivity of detecting any systematic change in sediment elevation. Starting in
June 2018,distances of 125 and 150 ft(38.1 and 45.7 m,respectively)were added to ensure elevation
samples were taken beyond the apparent apron of recently moved sand seen in aerial images (Figure 4).
These data have been provided to CSA and were analyzed for this report. Elevations were compared in a
2-way ANOVA using PROC GLM in SAS 9.2 after In+10 transformation (to avoid negative numbers and
address any non-normality of the data). Main effects were distance from the wavebreak and side of the
wavebreak,tested at individual dates along with assessment for interaction of main effects.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 11

Cis
Figure 4. Sand apron south of the wavebreak visually outlined from aerial imagery collected on
18 April 2018.
3.5 SUCCESS OF RELOCATED SAV
In 2016, prior to installation of the wavebreak,the State of North Carolina Department of Environmental
Quality and Coastal Resources Commission permit (Permit Modification No. 106-12) required any SAV
within the wavebreak structure footprint and the construction corridor north of the structure footprint
to be moved to the lee side of the structure onsite (CSA, 2017, 2018a, 2019, 2020). In May 2016,SAV
patches within the structure footprint and construction corridor were relocated to two planting areas on
the south side of the construction footprint situated in sand gaps among existing SAV. Percent cover of
SAV within planting areas was evaluated immediately after transplanting. Scientists navigated to
10 randomly-selected sampling stations (proportionally assigned to seven locations in the larger eastern
area and three in the smaller western area)within the planting areas using DGPS.To compare the
colonization of the planted areas to the surrounding natural reference area,five additional station
locations were randomly selected in the surrounding natural SAV area (reference area)within a
50-meter(164-foot) distance of the planting areas,for a total of 15 sampling stations.At each location, a
1-m2 (11-ft2) quadrat made of PVC was centered over each point and percent cover of SAV was assessed
using a modified Braun-Blanquet (BB) cover and abundance technique (Braun-Blanquet et al., 1972;
Kenworthy and Schwarzchild, 1997;Fourqurean et al.,2001). Within the quadrat, a BB scale value was
independently evaluated for percent cover of each SAV species as well as total SAV.Average BB scores
were then converted to percent cover for each area to allow interpolation of averaged BB scores that
fall between BB scale values (conversion is conducted by regressing the mid-point of percent cover
associated within the range covered by each BB scale value, on the associated BB scale value:
Percent Cover= 2.8108*[BB]2.2325)
NCDOT-FL-22-1830-2845-21-REP-01-FIN 12

3.6 WAVEBREAK EPIBIOTA—ESSENTIAL FISH HABITAT
Epibiota monitoring on the wavebreak was initiated in January 2017 through the establishment of
permanent monitoring stations,originally randomly-placed on the wavebreak, (CSA, 2017, 2018a, 2019,
2020). Besides its function of wave energy reduction,the wavebreak was anticipated to attract both
sessile and motile fauna and serve as EFH. Emphasis was placed on quantification of sessile fauna
colonization although anecdotal observations of motile faunal utilization were made during site visits.
Abundance as percent cover and composition of the epibiota were calculated for the following
categories: algae, barnacle, hydroid,oyster,cyanobacteria and total biota. Digital photographs were
recorded at each station as a time-zero (uncolonized) baseline against which subsequent epibiota
colonization (on both rock and concrete surfaces)was compared against subsequent surveys.Stations
were stratified by the sides of the wavebreak, 30 on the north side(predicted to be exposed) and 30 on
the south side, at relative tidal (vertical)elevations related to the individual wave attenuator tier
placement (high [top tier], middle [2"dlowest tier], and low [3rd lowest tier]) (Figure 3).Ten replicate
stations were randomly assigned per elevation strata on each side of the wavebreak for a total of
60 monitoring stations. Random locations were selected along the wavebreak,and a vertical elevation
was randomly assigned to each location (CSA, 2017).
Digital images were processed and analyzed using Coral Point Count with Microsoft Excel extensions
(CPCe)V4.1 software analysis program (Kohler and Gill, 2006). CPCe utilizes the random point count
method described by Bohnsack(1979)to accurately estimate percent cover of benthic organisms and
substrate from digital images. Rocks embedded in the disks had an average size of 112.4 cm2 and were
assigned 10 random points.The number of random points assigned to each image was then increased or
decreased proportionally to the size of the rock(s);the number of random points for rock images ranged
from four to 22. Because the area of concrete assessed was the same in each photo, all concrete images
were assigned the same number of random points (41), and points were restricted to the area of the
photograph containing only concrete. Random points were projected on each image, and the biota or
substrate located beneath each point was identified to the lowest possible taxonomic level (for the
time-zero images, no biota was detected). Data from each image were assembled in a spreadsheet for
percent cover calculations and subsequent comparative analysis.
3.7 SAV RESPONSE
Monthly surveys:The response of SAV to the wavebreak was first assessed using aerial imagery
provided by NCDOT in 2017 and 2018 (CSA, 2018a)to delineate and map SAV abundance. Utilization of
this imagery posed significant challenges in SAV interpretation and beginning in 2018, RK&K began
monthly aerial surveys of SAV(CSA, 2021a)with higher spatial resolution which promoted SAV mapping,
acreage estimation and, change (in SAV) analysis.Aerial surveys were conducted from 2018 to the
present time of this report(Table 2) by classifying areas of SAV occurring within the study area from
georeferenced, high-resolution, mosaicked data sets(CSA, 2021a).A process of unsupervised following
by supervised classification was followed using tools in Esri ArcGIS 10.6.1. software to perform the
SAV delineation (CSA, 2021a).
Table 2. Years and months during which aerial overflights were performed for SAV mapping around
the wavebreak.
2018 June,August,September,October
2019 March—December
2020 April—December
2021 April—December
NCDOT-FL-22-1830-2845-21-REP-01-FIN 13

The SAV delineation included segregation of the SAV cover data into forecast zones of influence(where
wave energy attenuation by the wavebreak was hypothesized to elicit a change in SAV cover organized
into the same strata described in the Bioturbation Study, Section 3.1 above)adjacent to the wavebreak
and in four surrounding, haphazardly-selected 2.5-acre reference areas outside of, but immediately
adjacent to,the forecast zone of influence of the wavebreak(CSA, 2021a).The reference areas were
situated to spatially bracket the forecast area of wave energy effects and were placed without
examination of their prior SAV coverage.SAV acreage were compared between forecast wave energy
reduction zones and the reference areas(CSA, 2021a)as well as among times of peak growing seasons
among years.
Change analysis:Anecdotal observations of imagery taken during the month of August 2021 suggested
that SAV may have substantially increased its cover across a broader extent of the shoals surrounding
the wavebreak than encompassed by the forecast wave energy reduction zones. Substantial colonization
of SAV appeared to have occurred especially between 2020 and 2021. Consequently,focus on just the
forecast wave energy reduction zones may not have detected important changes in SAV response to the
wavebreak and an effort was undertaken to produce a full landscape-scale assessment of changes in
SAV percent cover over time for the larger, 199.3 ac(80.6 ha)area captured in the monthly imagery
assessments. Using the already-collected imagery, change in SAV percent cover between the annual
periods of peak percent cover(August)from 2018 to the present and among months during the most
recent year of imagery(2020 to 2021)was undertaken using a different technique to identify any trends
and/or thresholds in the SAV percent coverage surrounding the wavebreak(CSA, 2021b).
A 5 m x 5 m grid cell mesh was constructed over the entire SAV survey area (approximately 32,000 grid
cells)and SAV percent cover computed per grid cell.The SAV percent cover of the most recent survey
was compared to that of the survey previous by grid cell for change(delta) in percent cover. Delta was
computed by subtracting the percent cover in a grid cell for a previous survey from the same grid cell in
the more recent survey [delta =more recent—previous])showing the progression of SAV change from
the previous survey to the more recent survey.This subtraction created a change in percent SAV percent
cover spatial matrix per pairwise date comparison which was then plotted to depict and visually assess
any apparent geographic pattern in SAV percent cover especially with respect to the wavebreak
(CSA, 2021b).
4 Results and Discussion
4.1 BIOTURBATION STUDY
The bioturbation study did not return definitive results. Only 20%of the mesh (8 out of 40 remesh
sheets)were relocated during the first post-installation survey in January 2017, approximately eight
months after initiation of the experiment in May 2016.The wavebreak was not yet constructed during
this time so comparisons could not be tested among wave energy reduction strata and low number of
remaining remesh (8)would preclude a statistically valid assessment even if the wall had been present.
Using the 8 remaining remesh to test against the 20 patch diameters with no remesh,there was no
significant difference (df=1,f=0.14,p=0.7071)among the change in SAV patch diameter between the
remesh and no remesh treatments,preliminarily indicating that bioturbation was not strongly
influencing the expansion of patch margins at that time. However,the passage of Hurricane Matthew in
October 2016 may have obscured effects (disturbance effects like Hurricane Matthew erode SAV
patches from their edge, much like sting ray bioturbation [Fonseca et al., 2000]). In October 2017,the
experiment was terminated and only the distance to patch edges were measured. That average distance
Waste ce mq6(Ns vie S� 'm002-4 7
✓NCDOT-FL-22-1830-2845-21-REP-0I-FIN 14

had reduced from 3.5 to 1.48 m suggesting the dynamic nature of SAV patch margins in this area
(CSA, 2017).
The role of bioturbation in SAV patch maintenance and the degree to which it may limit SAV patch
coalescence in beds experiencing a reduction in wind wave energy remains unknown. In North Carolina,
Townsend and Fonseca (1998)found that sting ray disturbance at SAV patch bed margins was
substantial and that in some of their sites,the entire unvegetated seafloor among SAV patches was
excavated by sting rays at least once a year. Other studies (Suchanek, 1983, Fonseca et al., 1994,
Valentine et al., 1994) also have revealed the role of bioturbation in the inhibition of SAV bed expansion.
Consequently,further study on the role of bioturbation as it may influence the strategy of using wind
wave energy reduction to promote SAV patch bed coalescence is warranted as high levels of
bioturbation have the potential to strongly affect the influence of wave energy reduction and either
slow or prevent SAV coalescence.
4.2 WAVEBREAK STRUCTURAL ASSESSMENT
In the 2019 structural assessment of the wavebreak(Appendix 5) it was reported that out of
101 pilings, 24(23.8%)exhibited some swaying movement and contact among the adjoining disks in the
presence of wind waves. However,this movement was not unanticipated (AR representatives, pers.
corn.) and may not represent a structural concern.As of 2019, 11 units had subsided, of these,five units
(the stack of 4 concrete disks on a piling)were experiencing periodic flow over the top disk(depending
on degree of subsidence and tide stage).As of August 2021, during up-close inspection of the
wavebreak, nine units had subsided to the point where water would regularly inundate them at high
tide. Onsite inspection of the individual units and the surrounding seafloor at that time indicated that
these few subsided disks do not appear to have resulted in any observable loss of wave attenuation
functionality overall.As of the 2019 report(Appendix 5)all the navigational warning lights on the
structure are intact and functioning correctly.The structure warning signs are in good condition.The
stationary benchmark survey datum on the structure was within +/-0.1-ft (0.0305-m)tolerance when
compared to the as-built drawings (Appendix 4).The navigational warning lights are still being checked
at periodic intervals by NCDOT.
4.3 WAVE ENERGY MONITORING
Long Term Wave Regime: Figure 5 shows the difference in the average daily significant wave heights
over time.Through visual examination of the data, there appears to be periods of time of where wave
heights trend to be higher or lower on one side of the wavebreak or the other. However, starting in
approximately September 2020,the previous periodicity of north versus south differences in significant
wave height changed and during the winter of 2020 and the spring of 2021 there was substantially,and
consistently higher wave energy measured on the north side of the wall than the south (Figure 5).As a
quality control measure the RBR sensors were removed during the final,July 2021 monitoring survey
and sent to the manufacturer for calibration. Examination of sensor calibration data provided by RBR in
the fall of 2021 indicated that this difference between the north and south sensors could have arisen
from sensor drift (a systematic difference was detected between the two sensors with the north sensor
reading up to 10 cm greater values)and consequently this difference is not interpreted as a systematic
shift in relative wave energy among the two sides of the wavebreak.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 15

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DIFF IN WAVE HTS(M):POS VALUE=NORTH HIGHER while NEG VALUE=SOUTH HIGHER
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Figure 5. Difference in hourly significant wave heights (m) between the north and south side of the
wavebreak for January 2017 through July 2021. A data gap (area of straight line)arose from
need to reposition and recalibrate sensors. Positive values=wave heights higher on north
side; Negative values=wave heights higher on south side.
As seen previously(CSA, 2020), a different picture emerges when only the top 5%of wave heights
(considered to be a threshold of defining extreme events) are evaluated. Statistically,the average wave
height of the top 5%of waves detected by the south-exposed sensor(Table 3)was significantly higher
(mean of 0.20 m on the south versus 0.13 m on the north:one-way ANOVA, df 1,f 1976.1, p<0.0001
[excluding the 2020-2021 data]). However,again excluding the 2020-2021 data,there were 4,074 events
where these waves were detected at the north-exposed sensor versus 814 at the south-exposed sensor
or five times as many events with waves of those composing the top 5%of all the wave heights detected
on the north side of the wavebreak(Table 3).Therefore, although average, minimum, and maximum
wave heights were slightly larger from the south,the number of the largest waves was far greater from
the north (and the maximum wave height of 0.44 m was still substantive), corroborating the original
expectations of what the wind field on the coas of North Carolina might produce, which is why the
forecast zone of reduction for the top 5%of win waves was larger on the south side of the wavebreak
(CSA, 2017). _. 1 "I k
Table 3. Summary statistics of the top 5%of wave heights measured at the two sensor stations on the
north and south sides of the wavebreak excluding 2020 to 2021 data.
Wavebreak Side Number of Mean Wave Minimum Wave Maximum Wave ` Range Wave
Observations Height(m) Height(m) Height(m) Height(m)
North 4074 0.13 0.07 0.44 0.37
South 814 0.20 0.14 0.51 0.37
NCDOT-FL-22-1830-2845-21-REP-01-FIN 16

Interruption by the wavebreak of the more frequent larger waves from the north and increased SAV
abundance south of and immediately adjacent to the wavebreak(see Section 4.7.2 SAV Response—
Change Analysis from Aerial Surveys, below)was consistent with the forecast of wind wave energy
interruption needed for SAV promotion.
WEMo model validation: Fine-scale model validation was attempted through opportunistic sampling
around the wavebreak but despite repeated attempts during visits when there were wind-generated
waves present, no valid regression could be established between the predicted (by WEMo) and
observed (from the RBR pressure sensor relocated to various positions around the wavebreak)wave
height values.Although WEMo has been shown to have robust prediction capabilities (Malhotra and
Fonseca, 2007)the attempt to down-scale the model results to the 50 m grid resolution was not
successful.This means that WEMo assessments should likely be applied to areas of lower spatial
resolution, potentially several times larger than the minimum spacing of the bathymetry data used in
the forecast (freely available bathymetric data are often at a resolution of approximately 80 m).
4.4 SEDIMENT ELEVATION
Far field—Digital Elevation Model (DEM):An ASV collected bathymetry data across the entire project
area in June 2016(Figure 6) and July 2021 (Figure 7).The surveys were conducted during both flood and
ebb tides and real-time tidal corrections were made to data collected. In 2016, MLLW depths ranged
from-0.5 to-2.0 m (-1.6 to-6.6 ft) across the site. MLLW depths in 2021 were similar to those observed
in 2016.The north and western portion of the site was notably shallower than the southeastern portion.
The DEM depicts the northeast-southwest tending shoal ridge of the larger shoal on which the
wavebreak is situated.The north and western portion of the site continued to be notably shallower than
the eastern portion.The change in sediment elevation from 2016 to 2021 is shown in Figure 8.Sediment
accumulation occurred south of and immediately adjacent to the wavebreak and somewhat to the north
and western side of the structure.These gains corroborate the near-field sediment elevation increase on
the south side of the wavebreak(see section Near field—Sediment Elevation Transects, below).The
shoals extending from the northeast to southwest across the project area showed some positive gains in
elevation, occasionally reaching slightly more than 0.3 m. However,there was some similar deepening
particularly in what appeared to be a slight trough ru ing northwest to southeast across a portion of
the shoal ridge. Some deepening was also evident to t a north and west of the wavebreak.
The accumulation of sediment along the northeast to southwest shoal ridge as well as the deeper trough
seen in the DEM corresponds to areas of increased SAV during these same times. It cannot be
determined with certainty whether the wavebreak contributed to this general far-field sediment
accretion, but the pattern of accretion is congruent with the effect of the wavebreak in reducing
exceedance winds(top 5%)from the northeast as well as persistent wave energy from the south
(i.e.,shoaling just north of the wavebreak). Moreover,this change did not occur until the wavebreak
was installed,so the timing of the shoaling is also consistent with an effect from the wavebreak. Some
spatially fine-scale increases and decreases in elevation embedded in the larger shoal mosaic are likely
the result of the survey line intersecting with SAV patch tops and adjacent troughs that have migrated to
different locations from 2016 to 2021. Deep troughs exist adjacent to SAV patches and like the patch,
position changes over time. Differences in elevation between an SAV patch top and adjacent
unvegetated seafloor sometimes reached 0.3 to 0.4 m (personal observation).
NCDOT-FL-22-1830-2845-21-REP-01-FIN 17

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Vehicle at the Bonner Bridge Seagrass Mitigation Site prior to construction of the wavebreak
(ultimate location of wavebreak shown). Soundings are in mean lower low water(MLLW).
Red dashed line shows the location and orientation of the shoal ridge referenced in text.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 18

/535'24"W 75'35'12W 15'35'0W 75`34'48W
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Figure 7. Digital elevation model constructed in 2021 from a survey by an Autonomous Surface
Vehicle at the Bonner Bridge Seagrass Mitigation Site five years post-construction of the
wavebreak. Soundings are in mean lower low water(MLLW). Red dashed line shows the
location and orientation of the shoal ridge referenced in text.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 19

t
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Figure 8. Differences in elevation among the two digital elevation models from 2016 and 2021.
Red dashed line shows the location and orientation of the shoal ridge referenced in text.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 20

Far field—Elevation Rods: Change in sediment elevation was computed among the replicate rods in
each of the wave energy reduction strata for the initial survey compared with all subsequent survey
dates (Appendix 6). In lieu of survey to survey changes which revealed no clear pattern of change over
time, comparisons with the first survey time were performed. A one-way ANOVA comparing changes in
sediment elevations at each survey versus that of the initial survey, by wave energy reduction strata
revealed that only comparisons among Survey 1 and Surveys 4 and 6 had differences in sediment
elevation among Reference and the High wave reduction zone and among the Reference and Low and
High wave reduction zones (Appendix 6). There has been no temporal sequence to these differences as
they have occurred in comparisons with both spring and fall surveys. However, differences were driven
by the sediment accumulation in the High wave reduction zone, closest to the wavebreak which is
consistent with the near-field transect surveys (below). A clear pattern of sediment accumulation across
wave energy strata emerged from this analysis. Sediment accumulated most in the High wave energy
reduction zone closest to the wavebreak with decreasing sediment accumulation with decreasing wave
energy reduction and distance from the wavebreak (Appendix 6). This pattern has remained consistent
among surveys, again corroborating the near-field transect surveys (below).
Near field—Sediment Elevation Transects:The surveys conducted by the subcontractor(SEPI
Engineering& Construction) revealed a significant scour pit formed under the wavebreak AR units
themselves. This sediment is suspected to be the source of a persistent light-colored band visible south
of the wall in aerial images (CSA, 2020). A comparison of sediment elevations by distance and side of
wall (north vs. south) showed a consistent pattern of erosion in the immediate proximity of the wall
(scour pit) but with little change in sediment elevation with distance on either side of the wavebreak
(CSA, 2020). In all cases where there was a significant difference in the sediment elevation between the
north and south sides of the wavebreak,the south side was shallower; this statistical difference has
been detected in 46%of the surveys (CSA, 2020).There has been no obvious temporal pattern of
when the south side was statistically different (shallower)than the north side of the wavebreak in this
near-field assessment. Importantly, while statistically different,the elevation differential between the
north and south side was in the range of about 0.15 m (6 inches). Despite being shallower,the south
side was still within the range of SAV growth as evidenced by the presence of numerous SAV patches
within this near-field survey and substantially increased SAV cover in this sand apron zone from 2020 to
2021 (see Section 4.7.2 SAV Response—Change Analysis from Aerial Surveys, below).
The ongoing(since surveys commenced in 2017) presence of an—3-ft (0.91-m) deep erosion pit under
the structure indicates that the experimental wavebreak is continually re-directing wave energy
downward to the seafloor, otherwise this pit would have filled in long ago. Future utilization of this
wavebreak design should consider this effect. Here,this ongoing redirection of wave energy may have
negatively affected the larger project plan by adding a mobile sand source to the location where the
highest SAV response (infilling of gaps among SAV patches) was forecast, and that area only experienced
substantial SAV colonization from 2020 to 2021 (see Section 4.7.2 SAV Response—Change Analysis
from Aerial Surveys, below). This apparent sand movement may have also negatively impacted the
relocated (from the wavebreak footprint prior to construction)SAV that was placed in the area where
the sand apron subsequently developed. 1 (\ >
The presence of the scour pit under the wavebreak has resulted in the full suspension of the four/ \ �'
concrete tiles composing the individual wavebreak AR units, above the sediment surface m
(a configuration for which the AR units are designed). While the structure was designed to support the C- Jl
disk stack and to accommodate movement, it has been noted that the units sway(<1 inch) and bump
together in even mild (e.g., less than 10 to 20 cm) wave heights, a behavior that might be reduced or
NCDOT-FL-22-1830-2845-21-REP-0I-FIN 21

eliminated if the units were in contact with the sediment surface. However,this movement has not
resulted in any visually apparent structural issues. Continued, periodic inspections of the structure over
time may be warranted to ascertain its resiliency in its state of disk stack suspension above the scour pit.
Filling of the scour pit with non-erodible material(e.g., carbonate rock, concrete A-jacks9, etc.) may also
be necessary to mitigate against future sand movement and storm-related impacts to the SAV now
colonizing to the south of and immediately adjacent to the wavebreak.
4.5 SUCCESS OF RELOCATED SAV
Prior to construction, SAV patches within the structure footprint and construction corridor were
relocated to two planting areas on the lee side of the wavebreak structure (CSA, 2020). SAV in the
planted area zones were monitored during all surveys. Representative photos of SAV within the planting
and reference areas throughout the monitoring program are in Appendix 7.Average percent cover of
SAV for the combined planting areas(eastern and western)versus the reference area throughout the
monitoring program are displayed in Appendix 8, Figure 1.
There was initial high cover(32.7%) in the planted areas as of May 2016 as measured immediately after
relocation, reflecting the high density of SAV installation, compressing all the SAV from the relocation
zone north of the wall into much smaller areas.This was intentional and was an attempt to quickly
create new, persistent SAV acreage. However as seen in Appendix 8, Figure 1,the planted areas had
very low survival.SAV subsequently began to colonize these areas and that may have been promoted by
persistence of small, relic portions of the relocated SAV(the randomly located quadrats did not
encounter SAV in the early surveys of the planted area but some SAV was observed). Later surveys
(7,8 and particularly survey 9 [July 2021]) showed increase in SAV coverage in the planted areas but this
was occurring at the same time broader colonization of the area was occurring south of and
immediately adjacent to the wall(see Section 4.7 SAV Response, below).
With this final survey,SAV monitoring has been performed for five years post-relocation. Percent cover
for the monitoring program to date, based on average BB scores, increased from the previous survey
(CSA, 2020)to 14.2%in the planting areas and 57.1% in the reference area. Fluctuation of cover among
surveys in both the planting and reference areas is likely the result of storm impacts (Hurricane
Matthew passed through the Pamlico Sound and surrounding areas on 8 and 9 October 2016,five
months after SAV relocation, prior to the installation of the wavebreak structure which may have had
significant impact on the newly relocated SAV), bioturbation, sand movement in this area (see
Section 4.4 Sediment Elevation,above) and an intrinsically patchy and shifting SAV distribution.
Mortality of SAV due to the relocation effort is not considered to be a significant factor based on
personal experience and these other sources of disturbance are typically the cause of SAV relocation
failures. In general,the SAV relocation was not highly successful but relocation to around the wavebreak
may now be more successful,given the natural recolonization that is now occurring in this area
indicating that natural SAV may have been able to overcome initial limitations to colonization in these
areas.
9 Hard Armor Erosion Control(conteches.com) Last accessed 18 March 2022.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 22

r
4.6 WAVEBREAK EPIBIOTA EFH ASSESSMENT
As in previous annual surveys (CSA, 2018a,2019, 2020),the percent cover of biota colonizing the
wavebreak substrate was assessed from photographs of each of the 60 fixed monitoring stations on the
wavebreak. Data were grouped first by substrate type (concrete or rock),then by vertical strata
(elevations related to the individual wave attenuator disk placement; high [top disk], middle [2nd lowest
disk],and low [3rd lowest disk]),and by orientation (north or south side of the wavebreak). Percent
cover results for concrete and rock monitoring stations along with a more detailed description of the
individual faunal category(algae, barnacle, hydroid, oyster,cyanobacteria and total biota) changes are
contained in Appendix 9,Tables 1 and 2, respectively. Representative photographs of colonized
substrate and sessile and motile fauna from the July 2021 survey are also displayed in Appendix 10.
On concrete portions of the wavebreak,colonizing biota included algae (primarily unidentified turf
algae), barnacles, hydroids, and oysters (Appendix 9,Table 1).To date,oysters have had no appreciable
cover on the high strata, and middle and low strata showed no appreciable cover until 2019.The highest
oyster cover(8.8%)thus far on concrete was found in 2019 on low strata on the south side. In the final
survey (July 2021)there were fewer live oysters found on any strata (average cover=1.3%).
On the embedded rock portions of the wavebreak disks,colonizing biota included algae, barnacles,
hydroids, oysters, and cyanobacteria (Appendix 9,Table 2).Oysters on rock substrate were first
recorded during the 2019 survey on middle and low strata and cover has generally increased within
these strata from 2019 to 2021 (Photo 3). However,oysters have not been observed on high rock strata
throughout the monitoring program. In the final survey (July 2021)there were substantially more
oysters found on rock than on concrete (average cover=10.6%and excluding the highest disks=15.9%).
This 8 to 12-fold higher abundance of oysters on rock versus concreate indicates the importance of
including suitable substrate, here in the form of granite rock, in construction of the AR disks to promote
oyster colonization.
In 2021,total epibiotic cover on the low elevation strata was nearly 100%for both rock and concrete
surfaces, irrespective of side of the structure (Figure 9a,b). Middle elevation strata, both rock and
concrete,and the high elevation strata for concrete also showed high cover, lagging slightly behind the
low strata. High elevation strata for rock continued to show the least cover. For all elevation strata,
concrete exhibited greater total colonization by biota versus rock on both north and south sides of the
wavebreak. Concrete typically exhibited greater colonization by algae and fauna (other than oysters)
versus rock substrate,while oysters have shown greater affinity for rock substrate.While a clear trend
of increased colonization has occurred,there were non-systematic fluctuations in cover among year,
side, and elevation strata,which is not uncommon for sessile intertidal communities. Overall, it appears
that the wavebreak has successfully created a persistent and extensive epibiotic community as a form of
essential fish habitat.Anecdotal observations also show utilization of the high strata by shorebirds
including ruddy turnstone (Arenaria interpres) (Appendix 10; Photo 10-8)during all surveys and fish
aggregation (Photo 4;02 October 2021) around the wavebreak,although the ecological significance of
such aggregations is unknown.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 23

j R
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Photo 3. Oyster colonization on rocks in a middle disk elevation (July 2021).Scale of photo is
approximately 30 cm wide.
II. 41144:4444444ttizzzlr' 4,.t_
t
•
Photo 4. Aerial image showing fish aggregation surrounding the eastern half of the wavebreak
(250 feet length)on 02 October 2021. Fish are likely mullet, Mugil cephalus(Image courtesy
of RK&K).
NCDOT-FL-22-1830-2845-21-REP-01-FIN 24

a) 100' a —�
substrate=concrete
-1410
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2018 2019 2020 2021 2018 2019 2020 2021 2018 2019 2020 2021
Low Med—� High—I Disk Strata
Figure 9. a) Percent cover of total epibiota for concrete portions of the wavebreak disks as of
July 2021. b) Percent cover of total epibiota for rock portions of the wavebreak disks as of
July 2021.
NCDOT—FL-22-1830-2845-21—REP-01—FIN 25

4.7 SAV RESPONSE
4.7.1 Monthly Aerial Surveys
Results of the month-to-month aerial surveys through 2020 conducted in a parallel effort (CSA, 2021a)
indicated the wavebreak was functioning as intended,and from this assessment appears to be
promoting a seasonally-variable, but positive, increase in SAV cover within all three wave energy
reduction strata, particularly the>66%and the 33 to 66% reduction strata closest to the wavebreak.
Overall, however,summing the reference-adjusted monthly gains and losses overtime starting in
August 2018, (n=22) resulted in a provision of 3.75 cumulative acres of added SAV services and an
average monthly standing gain of 0.19 acres. However, overall,these gains were offset by losses in other
months and using the reference areas as a basis for comparison, resulted in the average monthly
standing gain of 0.19 acres as of December 2020.
In Figure 10,the acreage of SAV in each of the wave energy reduction strata and reference areas is
plotted over time and in reference to tropical storms and hurricanes occurring in North Carolina during
the project period (CSA,2021a). Both the>66%and 33 to 66% RWE reduction strata, which are located
closest to the wavebreak structure and forecast to produce the greatest unit area effect on SAV
coalescence, appear to have experienced some adverse effects from proximity to the wavebreak in
2018 and 2019 due to sediment deposition adjacent to the structure from wavebreak-related scouring
(CSA, 2018b). All zones, including the reference areas,showed a downturn in acreage in spring of 2021,
but all zones showed a steady increase in SAV acreage through August 2021. However,the rate of
increase appears to have been slightly faster in the>66% and 33 to 66% reduction zones (steeper slopes
since April of 2021)than in either the 5 to 33%zone or the reference areas.
Some seasonal components to changes in SAV coverage was sometimes apparent in all three RWE
reduction strata. Most showed consistent decreases in SAV coverage between the fall and spring,
followed by increased SAV coverage between spring and summer. The red and green zones showed net
positive changes in SAV acreage in November or December,which may correspond to contributions
from increased biomass forZ. marina.These changes in cover represent the seasonally detectable
abundance of SAV in imagery.This fluctuation is normal for this area given the mix of Z. marina and
H. wrightii, both of which are at the edge of their respective geographic distributions.
Storm eventsi0 did not appear to have any visually discernible effect on SAV cover and total acreage for
the aerial assessment time period (CSA, 2021a).This is likely due to either storms not being in sufficient
proximity to generate damaging waves or when they were,there was often not enough water depth on
the shoal area during storm events to allow local wave propagation onto the shoal where the site is
located.
whttps://products.climate.ncsu.edu/weather/hurricanes/database/?search=location&loc=north%20carolina&Irad
=250&crit=gets&sort=year asc.(Reviewing the storm tracks and dates available in this interactive query tool
allowed us to pick the storms that influenced the NC coast). Last accessed 18 March 2022.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 26

80.00 (<-1) (2) (3) (4) (5) (6) (7) (8) (9)
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,Reference —+- >66%(red zone) 33-66%(orange zone) t 5-33%(green zone) /
Figure 10. Percent cover of total submerged aquatic vegetation (SAV) by aerial survey month in August 2018 through December 2020 for each /- / S
of the wave energy reduction zones. Dates are organized by survey; note blue bars indicating a change in the date sequence. Red vvvuuu(," o(1Iy
zone is the area near the wavebreak forecast to experience a>66%reduction in wave energy; orange zone,33 to 66% reductions /
green zone 5 to 33%reduction; reference area is from four adjacent reference areas outside the forecast wave energy reduction b
zones.All values are in percent cover. Data from December 2020 were not available for the green zone or the reference area. 7-0 v
Black vertical lines and numbers correspond to Tropical Storms and Hurricanes: (1) =Tropical Storm (TS)Chris on 7/10/2018 D e GQrn
[note<-indicating occurrence outside of the X-axis scale]; (2)= Hurricane (H) Florence on 9/13/2018; (3) =TS Michael on7
10/11/2018; (4) = H Dorian on 09/05/2019; (5) = H Humberto on 09/19/2019; (6) =TS Arthur on 05/18/2020; (7)=TS Fay on
07/09/2020; (8)= H Isaias on 08/03/2020; (9)=TS Claudette on 6/21/21.
•
NCDOT-FL-22-1830-2845-21-REP-01-FIN 27

75°35'24"W 75°35'12"W 75°35'0"W 75°34'48"W
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Figure 11. Change in percent cover of submerged aquatic vegetation (SAV) surrounding the wavebreak
for the months of August 2018 vs. August 2021.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 29

4.7.2 Change Analysis from Aerial Surveys
Monthly aerial surveys have provided more spatially complete and sequential comparisons of change in
SAV percent cover from year to year and month to month.These comparisons have been useful in
identifying the spatial and temporal trends of SAV on the shoal surrounding the wavebreak that were
not discernible in the previous approach where comparisons were made to arbitrarily selected reference
sites. Seasonal fluctuations are strongly associated with the spatial organization of a northeast to
southwest trending shoal ridge that passes across the site(Figure 11),with gains and losses in SAV
percent cover occurring often conversely east and west of that shoal.The shoal ridge crest emerged as
an area of comparatively low percent change in SAV percent cover over time. It should be noted that
prior to placement of the wavebreak, inspection of historical aerial imagery, including that from 2012 to
2015,just prior to construction,showed no indication of an SAV response to the ridge. SAV percent
cover across the shoal was visually uniform in a patchy distribution.We hypothesize that the placement
of the wavebreak may have stimulated an increase in the broader SAV percent cover on the shoal,
especially to the southwest of the structure along the shoal ridge.This larger landscape-scale shift in
increased SAV cover along the spine of the shoal ridge is visually apparent (Figure 12) and could have
influenced some of the reference areas selected for monthly survey comparisons of SAV change. If so,
any changes in reference area acreage in the month-to-month approach (CSA, 2O21a)that fell within
any landscape-scale shift arising from an effect of the wavebreak,would lead to an underestimation of
the promotion effect of SAV cover because reference area SAV cover would rise along with SAV in the
comparatively limited forecast area (i.e.,some reference areas were not independent estimates) as was
seen in Figure 10.As noted in Section 4.4, it is possible that this SAV promotion along the shoal ridge
was facilitated by the 0.3 to 0.5 m increase in shoal height from 2016 to 2021,which could in turn
potentially be an effect of the wavebreak structure.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 28

'5'35'24"'✓V '5`35"2'W 75'34'48
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Figure 12. Change in percent cover of submerged aquatic vegetation (SAV) surrounding the wavebreak
for the months of August 2020 vs.August 2021.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 30

The recent (2020 to 2021) area of increased SAV cover south of and adjacent to the wavebreak
(Figure 11) corresponded quite closely to the forecast area of highest wave energy reduction (CSA,
2021a), suggesting the predicted effect of increased SAV seafloor colonization and SAV patch
coalescence had begun to manifest itself. This persistent colonization south of and adjacent to the
wavebreak also indicates that the shoaling and sand dynamics observed in this ar a was apparently only
a temporary, albeit 4-year deterrent to SAV colonization. 1r
aSSG
Comparisons of SAV acreage by peak growing season (A st) in the forecast medium (wave energy
reduction; 33 to 66%) and high (wave energy reduct. ;>66%) wave energy reduction zones are shown
in Table 4.The low wave energy zone (5 to 33% ve energy reduction)was not considered in the SAV
change analysis because of its low proxi the wavebreak, making estimates of SAV response
conservative.This analysis shows th�utative ffect of the sand apron formation to the south of the
wavebreak on SAV acreage (these wave energy reduction zones are located south of and begin
immediately adjacent to the wavebreak; CSA, 2018a, 2019, 2020).
Table 4. Summary of SAV acreage change analysis within the model forecast high wave energy
reduction zone (>66% reduction) and the medium wave energy reduction zone (33 to
66% reduction) among the peak growing season (August), by year.
Area of Change
Wave Energy Number of Wave Average% Total Area (m2)vs. Change Change(%) Change(%)
Reduction Year 5 x 5 m EnergyCover of of SAV in vs.
Previous (m2)vs. vs.2018
% SAV in Grid Grid Cells Previous
Zone(%) Grid Cells Reduction 2 Year 20180n1y Only
Cells
Zone(m2) (m) Survey Survey
33_66 2018 960 24000 36.2 8677 n/a n/a
33_66 2019 960 24000 27.7 L 6654 -2024 77%
33_66 2020 960 24000 28.0 6728 75 101%
33_66 2021 960 24000 53.9 i 12931 6203 4254 192% 149%
>66 2018 171 4275 35.34 Lf 1511 n/a n/a
>66 2019 171 4275 16.38 D 700 -811 El 46%
>66 2020 171 4275 22.34 J 955 255 1$6%
>66 2021 171 4275 44.61 fl 1907 952 396 r 200% 126%
SAV acreage in the medium zone in 2019 declined to 77%of the 2018 cover(1 to 2 years after
wavebreak construction) but then began to recover exponentially. By August 2021 it had recovered to
149%of the 2018 value SAV acreage in the high zone in 2019 declined to 46% of the 2018 cover(1 to
2 years after wavebreak construction) but then also began a more linear recovery to 126%of the
2018 cover by 2021. With this rate of recolonization in the medium and high wave energy reduction
zones, 1.77 acres were gained in the last year. With the initial post-construction decline in acreage,
there has been a 1.15-acre net addition of SAV overall. If the rate of expansion continues then the target
of 1.28 ac would be reached in 2022.
From this pattern of SAV promotion it appears the sand apron and associated sand deposition and
movement that developed shortly after the wavebreak was installed had substantial, negative impacts
on adjacent SAV. It has taken over 4 years for SAV recovery to occur and will likely take another
several months to a year for SAV to recover from this impact and achieve the forecast SAV acreage
promotion.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 31

The slow pace of SAV colonization into the removal area north of and immediately adjacent to the
wavebreak suggests that this may be a zone of ongoing disruption of SAV colonization especially with
the higher and more frequent wave energy measured on this side of the wavebreak. However,
experimental relocation of SAV into this area from regional construction projects, if installed as large,
conterminous patches (e.g., Paulo et al, 2019) may be adequate to overcome any disruption of
colonization and establish persistent SAV coverage. Relocation of SAV to sand gaps south of the
wavebreak to around the wavebreak may now be more successful given the natural recolonization that
is now occurring in this area indicating that natural SAV may have been able to overcome initial
limitations to colonization in these areas.
5 Conclusions and Next Steps
5.1 DID IT WORK?
Because there is only one wavebreak structure,there is no replication and so utilization of traditional
statistical approaches to test for SAV promotion is challenging.Additionally, utilization of alternative
approaches such as BACI (e.g., Conner et al., 2016),which does not require replication of the treatment
(wavebreak)was complicated as the wavebreak may have had a larger, landscape effect that calls into
question utilization of some of the reference sites within the approximately 200-acre survey area.
Utilization of reference areas in the month-to-month aerial survey approach (CSA,2021a)that fell within
the potential effect of the wavebreak, may have underestimated the SAV promotion effect because SAV
cover within some reference areas may have also been influenced by the wavebreak and risen along
with SAV in the comparatively spatially limited forecast area (i.e., some reference areas were not
independent estimates).Therefore,in the absence of independent references sites,only a
semi-quantitative narrative is available to consider he various indicators of SAV promotion by th
wavebreak. ghal _s- S pJ�
To answer the question "did it work?",the answer appears to be yes.The development of highly (�2 -p' `c "
coalesced SAV coverage in the forecast location immediately south of and adjacent to the wavebreak S� -S
•
(Figures 11 and 12) indicates that SAV finally underwent a shift to a new state of more continuous cover.
SAV patches north of and not in proximity to the structure did not undergo this coalescence.
Additionally,this increase in SAV may have promoted a cascade of increased SAV cover to the southwest
along the shoal, likely the result of increased shoaling that began concomitant with the installation of
the wavebreak(Figure 8). Figure 13 shows an aerial image of the shoal area from 2015 along with the
future wavebreak location.That image shows a concentration of continuous SAV to the southwest with
a gradient of decreasing cover to the northeast,through and beyond the wavebreak location. Based on
examination of freely available imagery,this was the status of the shoal for approximately a decade
prior to wavebreak installation and is markedly different from the current status,where SAV cover has
coalesced from the historical area to the southwest all the way northeast to the wavebreak(Figure 14).
Although there is no quantitative means to definitively link the cause and effect of this shoaling and SAV
promotion to the southwest of the wavebreak, it is highly coincident with the installation of the
wavebreak,and the strong possibility exists that the wavebreak contributed to a cascade of downstream
effects that has substantially increased SAV across the shoal.The duration of this apparent increase will
need to be examined over time to determine its persistence.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 32

Figure 13. 2015 image of wavebreak location showing patchy submerged aquatic vegetation in the
area surrounding the wavebreak. Image width is approximately 1.2 miles.
Source:Albemarle-Pamlico Estuarine Research Program.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 33

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Figure 14. August 2021 image of wavebreak survey area showing submerged aquatic vegetation in the
area surrounding the wavebreak. Each arm of the wavebreak is 250 ft for a total length of
500 ft.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 34

Starting in April 2021,there was a widespread increase in SAV both near the wavebreak but also along
the entire shoal ridge area. However, as seen in Figure 10 and in the Change Analysis (Section 4.7.2),the
increase was disproportionately greater in the>66(high)and 33 to 66%(medium) RWE reduction
zones.The increased SAV cover in the (forecast) high and medium wave energy reduction zones has now
begun a substantial promotion of SAV acreage and have reached 90%of the initially forecast acreage.
From this pattern of SAV promotion it appears that the sand apron and associated sand deposition and
movement that developed shortly after the wavebreak was installed had substantial, with negative
impacts on adjacent SAV. It has taken over four years for SAV recovery to occur and if this recent
promotion persists,will likely take another several months to a year for SAV to fully recover from this
impact and achieve the forecast SAV acreage promotion of 1.28 acres. Nonetheless,given all the
ecological factors at play and the various steps taken to develop an SAV promotion response forecast
(application of a wave energy/SAV response model with an r2 of 0.75 [Figure 2]),only a 10%deviation
from that forecast acreage may be considered a very robust outcome.
The role of bioturbation in maintaining SAV bed patchiness in this area remains unknown. For example,
a localized reduction in bioturbation could explain at least in part the increase in SAV abundance south
of and immediately adjacent to the wavebreak, but this remains unknown. Additional experimental
work is needed to separate the role of wave energy from bioturbation in maintaining SAV bed
patchiness to formulate effective SAV restoration plans.Also from an experimental perspective,
relocation of SAV from regional construction projects into the area north of and immediately adjacent to
the wavebreak, if installed as large, conterminous patches (e.g., Paulo et al., 2019) may be adequate to
overcome any disruption of colonization and establish persistent SAV patch beds.
Shoaling occurred to the south side of the wavebreak but not to an extent that prevented SAV
colonization up to the margins of the structure's underlying scour pit.This shoaling was not just localized
to the wavebreak but may have been part of the larger, landscape-scale shift in shoal water depth, as
was evidenced by the before and after DEM analysis. Filling of the scour pit underneath the wavebreak
should be considered as a follow-on mitigation action to eliminate the potential for future sediment
movement and impact to the SAV on the south side and immediately adjacent to the wavebreak.
Because this fill would occur primarily under the wavebreak for which mitigation was already performed
(relocation of adjacent SAV)for at least the north side of the structure,further need for compensatory
mitigation for the fill itself may be minor.
The north side of the wall experienced almost five times the frequency of the top 5%of wave heights
than the south side. Diminution of these more frequent, larger wave events likely provided the
necessary reduction in disturbance south of and immediately adjacent to the wavebreak to trigger an
increase in SAV coverage.The intervening time appears to have been needed for SAV to overcome the
disturbance of ongoing sand movement,explaining at least in part the delay in SAV response to
colonization on the south side of the wavebreak(the expectation was that promotion of SAV
coalescence would have begun to occur immediately after construction of the wavebreak). Based on
visual inspection of the aerial imagery it appears that SAV recruitment and existing patch expansion and
coalescence were the basis of the SAV increase.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 35

Finally,the wavebreak structure has and continues to provide substantial essential fish habitat
services. Seabirds have been consistently observed on the wavebreak(e.g., brown pelican
[Pelecanus occidentalis], herring gulls [Laurus canus], ruddy turnstone [Arenaria interpres],various
unidentified terns). Epibiotic cover(algae, barnacle, hydroid, oyster, cyanobacteria) of the structure has
steadily increased to nearly 100%of the regularly submersed portions of the wavebreak. Oyster
(Crassostrea virginica) colonization has also increased, particularly on the granite rock portions to the
structure to an average of 10.6%cover.Sheepshead (Archosargus probatocephalus) have been observed
under and around the structure and other species including oyster toadfish (Opsanus tau),feather
blenny(Hypsoblennius hentz),and juvenile Atlantic spadefish (Chaetodipterus faber) have been
observed in association with the structure (CSA, 2020).Anecdotal information from local contractors
utilized for survey support suggested that the structure also provides some attraction for recreational
anglers, although none have been observed during site surveys(Photo 4).
5.2 LESSONS LEARNED
Perhaps the most important lesson learned was that the wavebreak strongly influenced sand transport
and shoaling. The unanticipated formation of the scour pit under the structure and the formation of a
persistent, dynamic sand shoal to the south of and immediately adjacent to the wavebreak likely
impeded SAV colonization. Planning for this erosion with a contingency for addition of non-moveable
material into a scour pit,should it begin to form, may be needed in future applications.
The unanticipated, potential influence of the wavebreak on a larger extent of the shoal and selection of
references sites also needs future planning. Initial selection and monitoring of reference areas from a
diversity of nearby shoals with patchy SAV beds at similar water depths would have provided an
improved comparative analysis of the wavebreak SAV promotion effect and allowed utilization of a BACI
analysis.
5.3 FUTURE STEPS AND APPLICATIONS
Continued aerial mapping of SAV and interpretation of SAV cover around the wavebreak should occur at
least seasonally for the next 3 to 5 years. Given the late start of the SAV promotion process,this
mapping is needed to quantify the persistence of SAV cover around the wavebreak and ensure
documentation of"more continuous, persistent SAV acreage"which was the goal of this experimental
mitigation.
Although additional time was needed for the SAV promotion to overcome the apparent disturbance of
the sand apron,the promotion eventually took hold,validating this approach as appropriate for use in
mitigation of other bridge impacts.Any SAV increase in acreage above that provided for the original
Bonner Bridge impacts may be considered as a dividend for application against impacts from other
NCDOT projects.
Additional manipulation at the current wavebreak location has the potential to further promote SAV
coalescence. Addition of a wavebreak to the south of the existing one, using an alternative wavebreak
design that does not create a similar sand apron, would eliminate the wave disturbance from the south
and make for an even more quiescent wave energy zone between the two structures.Th&extent
(length) and location (distance from the existing wavebreak)to create this adde quiescence ould
require further examination.
Jv\� (1)2-SS I
—SS
NCDOT-FL-22-1830-2845-21-REP-0I-FIN 36

The north side of the wavebreak from which SAV was relocated has shown signs of recovery.This area
meets the requirements of a mitigation site as it was anthropogenically disturbed and that disturbance
ceased.This area could therefore serve as a relocation zone for SAV from other NCDOT projects in the
Pamlico Sound area. Relocation of SAV to this location should focus on creating patches of the same or
greater size than the existing,smallest persistent patches near the wavebreak.
Measurements of sediment elevation response need not be conducted monthly as was done here for
much of the project timeline.The monthly surveys were useful because they allowed documentation of
not only the stability of the near-field sediment elevation change but also how quickly that occurred.
With the benefit of the three sediment elevation approaches employed in this monitoring program, it
can now be recommended that a combination of quarterly near-field and biannual (every 2 years)
far-field sediment elevation surveys in the form of a DEM would have best captured the sediment
elevation dynamics.
Perhaps the most significant unknown that can influence the efficacy of the SAV promotion process
through wave energy reduction is the role of bioturbation.A study to assess the role of
bioturbation impacts can be performed at any time. However,this should be undertaken by an
organization with frequent access to the study site to provide maintenance of any experimental
manipulations (e.g., ensuring exclusion devices are present and functioning). Such a task could be done
efficiently in concert with other planned activities on the site and at a minimal cost.The value of such a
study would be to calibrate expectations of SAV promotion from wave energy reduction alone and
determine whether bioturbation mitigation was needed to optimize SAV promotion.
NCDOT-FL-22-1830-2845-21-REP-01-FIN 37

UAS Survey of the Bonner Bridge SAV Mitigation Site —
2021 Summary Report
March 2022
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Prepared for: Prepared by:
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Rummel Klepper & Kahl CSA
8601 Six Forks Road CSA Ocean Sciences Inc.
Forum 1, Suite 700 8502 SW Kansas Avenue
Raleigh, North Carolina 27615 Stuart, Florida 34997
.:.- T� [J]PFC ,
CERTIFIED AUTHORIZED PROVIDER

Plettkik
C SA
CSA Ocean Sciences Ina.
UAS Survey of the Bonner Bridge SAV
Mitigation Site — 2021 Summary Report
DOCUMENT NO. CSA-RKK-FL-22-81656-3676-02-REP-01-FIN
Internal review process
Version Date Description Prepared by: Reviewed by: Approved by:
INT-01 02/15/2022 Initial draft for J. Pennell Mark Fonseca J. Pennell
science review
INT-02 02/17/2022 Technical review J. Pennell K. Metzger J. Pennell
Client deliverable
Version Date Description Project Manager Approval
01 02/21/2022 Client deliverable J. Pennell
FIN 03/04/2022 Client deliverable J. Pennell
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the CSA Document Production Department.

Table of Contents
Page
List of Tables iii
List of Figures iv
1.0 Background 1
2.0 Methods 1
3.0 Results and Discussion 4
3.1 ACREAGE SUMMARY 4
3.2 AUGUST 2018 (BASELINE) VERSUS 2021 SURVEYS 4
4.0 Conclusions 16
5.0 Literature Cited 17
List of Tables
Table Page
1 Acreage of each of the three Representative Wave Energy(RWE) strata and
reference areas assessed from wave energy reduction modeling 3
2 Significant storm events either Tropical Storm (TS) or named Hurricanes
(no designation) for North Carolina and the dates of the first imagery obtained for
this project following the storm event 4
3 Total submerged aquatic vegetation (SAV) acreage by survey month in 2018 for each
of the wave energy reduction zones 6
4 Total submerged aquatic vegetation (SAV) acreage by survey month in 2019 for each
of the wave energy reduction zones 7
5 Total submerged aquatic vegetation (SAV) acreage by survey month in 2020 for each
of the wave energy reduction zones 7
6 Total submerged aquatic vegetation (SAV) acreage by survey month in 2021 for each
of the wave energy reduction zones 8
7 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2018
for each of the wave energy reduction zones 8
8 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2019
for each of the wave energy reduction zones 9
9 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2020
for each of the wave energy reduction zones 9
10 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2021
for each of the wave energy reduction zones 10
11 Total submerged aquatic vegetation (SAV) by survey month and summed for all
reference areas and all wave energy reduction zones, respectively 10
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN iii

List of Figures
Figure Page
1 Overview of the Bonner Bridge wave-break submerged aquatic vegetation
monitoring program study area showing the wave-break structure, Representative
Wave Energy (RWE) reduction strata, and reference areas overlain on baseline
imagery from August 2018 2
2 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2021 for each of the wave energy reduction zones 11
3 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2021 for all of the three wave energy reduction
zones combined 12
4 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2021 for the red wave energy reduction zone 13
5 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2021 for the orange wave energy reduction zone 14
6 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through December 2021 for the green wave energy reduction zone 15
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN iv

1.0 Background
In response to the anticipated loss of submerged aquatic vegetation (SAV) habitat caused by the
replacement of the Herbert C. Bonner Bridge over Oregon Inlet, North Carolina, a wave-break structure
was constructed with the purpose of experimentally modifying existing, patchy SAV habitat by
attenuating wave activity to test the ability of wave reduction to promote more continuous, persistent
SAV coverage. After field surveys and wind wave modeling to guide wave-break size and placement,the
wave-break structure was constructed and installed between November 2016 and January 2017.
In order to evaluate effects of the wave-break structure on the potential enhancement of SAV cover, a
long-term, SAV monitoring program was established, with Time Zero data collection in January 2017
immediately following wave-break construction.The North Carolina Department of Transportation
(NCDOT) contracted Rummel Klepper and Kahl (RK&K)to lead this monitoring program. CSA Ocean
Sciences Inc. (CSA) was subcontracted by RK&K to support the monitoring survey design and perform
delineation of SAV cover. Data interpretations were performed from datasets collected in 2017, 2018,
2019, and 2020, and were reported in annual summary reports (CSA, 2019; CSA, 2021a; CSA, 2021b).
This report presents the results of the data interpretations performed from data collected in 2021 and
compares them to August 2018 baseline data.
2.0 Methods
The long-term SAV monitoring program for the wave-break structure includes delineation of SAV cover
from data collected multiple times per year. In 2021, it was determined that because the August 2018
data set was the first data set recorded during the seagrass growing season, it should provide a more
suitable baseline data set than the Time Zero January 2017 data. Moreover, August 2018 represents the
peak of the growing season for the visibly dominant, sub-tropical SAV, Halodule wrightii. Subsequent
data were collected in September and October of 2018, in March through December of 2019, in April
through December of 2020, and in April through November of 2021.This data series has allowed change
analyses of SAV cover following wave-break structure construction (CSA, 2021c),which based on life
history of the primary SAV species on the site (H. wrightii, Ruppia maritima,Zostera marina) should
encompass a time frame when responses by SAV cover could occur(Kenworthy et al., 1982; Thayer
et al., 1984; Fonseca and Bell, 1998).
The SAV delineation includes a forecast zone of influence (study area; where wave energy attenuation
by the wave-break is hypothesized to elicit a change in seagrass cover) adjacent to the wave-break
structure and four surrounding, haphazardly-selected 2.5-acre reference areas (Figure 1) outside of, but
immediately adjacent to,the forecast zone of influence of the wave-break structure.The reference
areas were situated to spatially bracket the forecast area of wave energy effects and were placed
arbitrarily without examination of their initial SAV coverage. Specifically,the study area has been
organized into the following strata based on an estimate of the potential reduction in Representative
Wave Energy (RWE; Malhotra and Fonseca, 2007) caused by the wave-break structure (Figure 1; See
Table 1 for strata acreages):
1. >66% reduction in RWE (red zone);
2. 33 to 66% reduction in RWE (orange zone);
3. 5 to 33% reduction in RWE (green zone); and
4. Reference area (forecast as having less than a 5% reduction in RWE as the result of the position of
the wave-break structure).
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 1

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Figure 1. Overview of the Bonner Bridge wave-break submerged aquatic vegetation monitoring
program study area showing the wave-break structure, Representative Wave Energy(RWE)
reduction strata, and reference areas overlain on baseline imagery from August 2018.The
wave-break structure is the black, chevron-shaped line just north of the red zone.
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 2

Table 1. Acreage of each of the three Representative Wave Energy (RWE) strata and reference areas
assessed from wave energy reduction modeling.
Area of SAV Assessment Acres
Reference 9.88
>66%(red zone) polygon 0.87
33-66%(orange zone) polygon 5.16
5-33%(green zone) polygon 50.44
SAV=submerged aquatic vegetation.
Datasets were collected in January 2017 (Time Zero) by CSA, in August(baseline) through October 2018,
in March through December 2019, in April through December 2020, and in April through November
2021 by RK&K. CSA performed interpretation of datasets for the wave-break site using GIS. SAV cover
was determined by classifying areas of SAV occurring within the study area from georeferenced,
high-resolution mosaicked data sets. Each data set had a resolution of 4 cm (1.57 in).The data was
sometimes subdivided into separate classification areas of interest(AOI) based on similar pixel spectral
signature ranges, often at the scale of individual image tiles(e.g., approximately 35 acres). Where image
quality permitted, separate classification of each AOI helped to eliminate variations in reflectance and
environmental conditions across the entire study area in order to reduce classification confusion. An
unsupervised classification was then performed on each classification AOI using a combination of iso
cluster and maximum likelihood techniques using Esri ArcGIS 10.6.1. software.
After running the unsupervised classifications, the resulting SAV delineations in each AOI were refined
by manually denoting visually apparent classes of SAV and classes of non-SAV(primarily seafloor
substrate). Spectral noise and holes within the classification results were removed and corrected using a
combination of Esri ArcMap (10.8.0.)tools including Majority Filter, Region Group, Set Null (enhanced
boundary edges and removed groups of small non-contiguous pixels that were smaller than 6 pixels),
and Eliminate Polygon Part(eliminated areas that were less than 8 square feet). Lastly, a manual
classification technique was then applied to the classification with guidance from a GIS analyst
experienced in SAV delineation and a SAV biologist with extensive experience in North Carolina SAV
systems.This consisted of removing areas of over-classification (classifying non-seagrass areas as
seagrass) and adding-in (digitizing) areas where under-classification (classifying seagrass as
non-seagrass) occurred, again based on visually apparent SAV cover in the data. Comparisons of cover
over time could be made against the August 2018 baseline. SAV cover in August (mid-summer) allows
comparisons for changes in marine SAV cover measured during the growing season, which generally
ranges from March through September in North Carolina (Kenworthy et al., 1982; Thayer et al., 1984;
Fonseca and Bell, 1998).Therefore, each monthly survey could be compared to August 2018, which
provided the greatest possible temporal distance among peak growing season conditions for assessment
of change in SAV cover.These comparisons captured the seasonal dynamics of the SAV habitat.
Comparisons of monthly survey data revealed general seasonal trends of cover increase and decrease.
Additional calculations were made to determine reference-adjusted gains and losses in acreage and
percent cover per month by energy zone.
At the request of NCDOT, storm events were added to figures showing change in SAV abundance over
time. Table 2 shows significant storm events (Tropical Storms and Hurricanes)that have occurred during
the time of imagery acquisition for this project and the dates of the first imagery obtained for this
project following the storm event.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 3

Table 2. Significant storm events either Tropical Storms (TS) or named Hurricanes (no designation)for
North Carolina and the dates of the first imagery obtained for this project following the
storm event. Numbers correspond to storm events shown in figures.
Dates of first imagery
Storm Number Storm Name Year Storm Date following storm
event
1 TS Chris 2018 7/10/2018 8/26/2018
2 Florence 2018 9/13/2018 10/2/2018
3 TS Michael 2018 10/11/2018 2/26/2019
4 Dorian 2019 9/5/2019 9/20/2019
5 Humberto 2019 9/19/2019 9/20/2019
6 TS Arthur 2020 5/18/2020 5/26/2020
7 TS Fay 2020 7/9/2020 7/26/2020
8 Isaias 2020 8/3/2020 8/10/2020
9 TS Claudette 2021 6/21/2021 7/23/2021
10 Elsa 2021 7/8/2021 7/23/2021
3.0 Results and Discussion
3.1 ACREAGE SUMMARY
Total acreage in each zone by month is given in Tables 3,4, 5, and 6. In 2018, the red zone (area of
highest forecast wave energy reduction) ranged from 0.31 to 0.37 acres of SAV, the orange zone
(moderate wave energy reduction) ranged from 1.90 to 2.36 acres, the green zone (lowest wave energy
reduction) ranged from 14.87 to 15.24 acres, and the reference areas ranged from 1.88 to 1.97 acres
(Table 3).
In 2019,the red zone ranged from 0.11 to 0.37 acres of SAV, the orange zone ranged from 1.15 to
2.14 acres, the green zone ranged from 8.82 to 16.31 acres, and the reference areas ranged from 0.31 to
2.00 acres (Table 4).
In 2020,the red zone ranged from 0.13 to 0.41 acres of SAV,the orange zone ranged from 1.07 to
2.14 acres,the green zone ranged from 10.91 to 15.62 acres, and the reference areas ranged from
1.32 to 2.07 acres (Table 5). In December 2020, data from the reference area and the 5 to 33% RWE
reduction stratum were incomplete due to poor conditions and resultant low image quality. Therefore,
the acreage and percent cover of SAV for these two areas in December 2020 were not calculated.
In 2021, the red zone ranged from 0.31 to 0.71 acres of SAV,the orange zone ranged from 1.41 to
3.22 acres, the green zone ranged from 12.27 to 21.00 acres, and the reference areas ranged from
0.81 to 3.23 acres (Table 6).
3.2 AUGUST 2018 (BASELINE)VERSUS 2021 SURVEYS
Percent cover of SAV for the Bonner Bridge wave-break study area, based on the GIS classification of
prior datasets from between August 2018 (Baseline) and December 2020, can be found in Tables 7, 8,
and 9.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 4

Percent cover of SAV for the Bonner Bridge wave-break study reference area, based on the GIS
classification of datasets from August 2018 (Baseline) was 19.1%cover. Percent cover of SAV for the
reference area between April 2021 and November 2021 ranged from 8.2%to 32.7%cover (Table 10)
with a mean of 24.1%.The highest reference area cover among all surveys in 2021 was observed in
September 2021 and the lowest in April 2021. This was not unexpected based on the timing of the
surveys at the end of growing season for Halodule wrightii in late summer and the start of the growing
season in early summer, respectively.
Percent cover of SAV in August 2018 for the >66%, 33 to 66%, and 5 to 33% RWE reduction strata were
42.9%,41.6%, and 30.1%, respectively (Table 10). In 2021, percent cover of SAV for the >66% RWE
reduction stratum ranged from 35.6%to 81.1%cover with a mean of 65.9%. Percent cover of SAV for
the 33 to 66% RWE reduction stratum ranged from 27.3%to 62.5%cover with a mean of 50.5%. Percent
cover of SAV for the 5 to 33% RWE reduction stratum ranged from 24.3%to 41.6%cover with a mean of
35.5%.
The changes in percent cover of SAV from August 2018 to November 2021 are plotted in Figures 2
through 6. Figure 2 shows the individual RWE reduction strata plotted against the reference areas.
Figure 3 combines the three separate RWE reduction strata into a single percent cover value for each
survey and plots these values against the reference areas. Figures 4, 5, and 6 plot the change in percent
cover of SAV for each of the three RWE reduction strata (>66%, 33 to 66%, and 5 to 33% RWE,
respectively) against the reference strata.
In April 2021,the reference and 33 to 66% RWE reduction stratum showed slightly lower percent cover
values than the>66% or 5 to 33% RWE reduction strata when compared to their respective baseline
values in August 2018. From April to August 2021, percent cover of SAV within all three RWE reduction
strata and the reference area increased, as would be expected over the SAV growing season. All three
RWE reduction strata and the reference area showed consistent increases in SAV cover during this time,
with increases observed every month. From August to November 2021, percent cover of SAV showed a
general leveling off within the reference and all three RWE reduction strata, also in line with what would
be expected at the end of the SAV growing season.
A summarization of the total SAV acreage by month for the reference areas and all RWE reduction
strata combined is shown in Table 11. The total SAV acreage in the reference zones ranged from 0.31 to
3.23 acres with a mean of 1.82 acres(standard deviation 0.68) while the total SAV in all RWE reduction
strata ranged from 10.82 to 24.93 with a mean of 17.44 acres (standard deviation 3.58).
Whether or not storm events appeared to affect SAV abundance depended upon when in the growing
season the storm event occurred. If the storm occurred late in the growing season (August to
September) or in the fall,then a decrease in SAV following the storm event was observed (concurrent
with the natural seasonal decrease in SAV). If the storm event happened earlier in the growing season
(May to July)then a continued increase in SAV cover after the storm event was observed (concurrent
with the natural increase in SAV during the growing season).
Following Hurricane Florence in September 2018, a sharp decrease in SAV cover in the >66%and
33-66% RWE reduction strata was observed (Figure 2).This decrease was greater than the decrease
observed in the reference or 5-33% RWE reduction stratum, indicating that, during this storm event,
proximity to the wave-break accelerated SAV loss. Monitoring of the sediment in the vicinity of the
wave-break has observed the formation of an apron of sand on the south side of the wave-break,
possibly the result of scouring of sediment from underneath the wave-break(CSA 2022, in review).
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 5

This scouring was observed as early as April 2018, prior to the first storm event in July 2018, so the
scouring cannot be attributed to only storms but also to regular tidal currents over time. However,
scouring could increase during storm events, leading to increased loss of SAV through burial by
sediment.
Note in Table 2, that when storms occurred surveys were conducted within 1 month following the event
(with the exception of Tropical Storm Michael where an assessment followed the event by four months),
which is not enough time for SAV seafloor to recover had there been any substantial, storm-induced
reductions in seafloor SAV coverage (with the exception of Hurricane Florence, as noted above).Visual
assessment of SAV response to storm events (Figures 2 to 6) saw general decrease in SAV across zones
in Spring of 2019 following storms in the fall of 2018 but that is also a period of natural SAV seasonal
decline.The two storms in 2019 did not appear to be related to a drop in SAV cover and in 2020 and
2021 SAV coverage actually increased following storm events.The lack of any apparent correlation of
most storm events with observable changes in SAV cover is likely the result of two factors. One factor is
the proximity of the storm to the site (the storms listed are for the entirety of North Carolina). But
perhaps more important is the second factor, and that is whether there was enough water on the site to
allow damaging (to SAV) wave energy on the site.The project team observed that for many storm
events the wind drove water levels down which prevents the introduction of wave energy onto the site.
A more detailed study of wave energy and water level from the on-site wave sensors during storm
events would be needed to ascertain whether the existence of any particular storm event had the
potential to influence SAV cover as has been seen for previous storm events in North Carolina (Fonseca
et al. 2000).
There was also a drop in SAV cover between December 2020 and April 2021 not unlike that seen in the
fall of 2018. After review of meteorological data during this time period', in this case there were no
obvious storm events that could have led to this decline. Rather, it is hypothesized that seasonal
variation (i.e., winter decline of H. wrightii) may have produced this pattern of SAV abundance.
Table 3. Total submerged aquatic vegetation (SAV) acreage by survey month in 2018 for each of the
wave energy reduction zones. Red zone is the area near the wave-break structure forecast to
experience a >66% reduction in wave energy;orange zone, 33 to 66% reduction; green zone
5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by
the wave-break structure. Cells with blue shading are scaled proportionally. For readability,
cells with green shading (green zone) are scaled proportionally but only for the green zone
due to their larger value range. All values are in acres.
Area of SAV Assessment Baseline Sep'18 Oct'18
Aug'18
Reference 11111 .1•
>66%(red zone) I 0.37 I 0.37 0.31
33-66%(orange zone) 11 1
5-33%(green zone) algal 4 14.87
' North Carolina State Climate Office—http://climate.ncsu.edu.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 6

Table 4. Total submerged aquatic vegetation (SAV) acreage by survey month in 2019 for each of the wave energy reduction zones. Red zone is
the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33-66% reduction;
green zone 5-33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. Cells
with blue shading are scaled proportionally. For readability, cells with green shading (green zone) are scaled proportionally but only
for the green zone due to their larger value range.All values are in acres.
Area of SAV Assessment Baseline
Aug Mar'19 Apr'19 May'19 Jun'19 Jul'19 Aug'19 Sep'19 Oct'19 Nov'19 Dec'19
Reference ' CI 91 tl 0.31 IMBIII 1511
>66%(red zone) © 0.37 tj 0.20 Q 0.19 I 0.21 I 0.21 I 0.24 I 0.17 I 0.12 0.11 11 0.15 0 0.12
33-66%(orange zone) in W35 i 1 ' -T1 41F.
5-33%(green zone) r17 t11.82 t 8,82 Mill,331 .33 ) M6 31 C 4.90 t 15.59 x 13.13
Table 5. Total submerged aquatic vegetation (SAV) acreage by survey month in 2020 for each of the wave energy reduction zones. Red zone is
the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33-66% reduction;
green zone 5-33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. Cells
with blue shading are scaled proportionally. For readability, cells with green shading (green zone) are scaled proportionally but only
for the green zone due to their larger value range. All values are in acres.
Area of SAV Assessment Baseline Apr'20 May'20 Jun'20 Jul '20 Aug'20 Sep'20 Oct'20 Nov'20 Dec'20
Aug'18
Reference : _ MI All *
>66%(red zone) II 0.37 0.13 0.13 II 0.19 11 0.23 F 0.24 E 0.27 I] 0.28 F 0.36 II 0.41
33-66%(orange zone) ATI .. ti1 1111 N`i
5-33%(green zone) Et5,17 ki 10.91 II 14.26 V 13.72 t 15.62 ) ':_15.4614.84 =15.5315.40_
*=No calculation due to coverage constraints.
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 7

Table 6. Total submerged aquatic vegetation (SAV) acreage by survey month in 2021 for each of the wave energy reduction zones. Red zone is
the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33-66% reduction;
green zone 5-33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. Cells
with blue shading are scaled proportionally. For readability, cells with green shading (green zone) are scaled proportionally but only
for the green zone due to their larger value range. All values are in acres.
Baseline Aug
Area of SAV Assessment ,18 Apr'21 May'21 Jun'21 Jul'21 Aug'21 Sep'21 Oct'21 Nov'21
Reference I0.81 _ 5j 50 1E1.87 Ilifss MEL INID4
>66%(red zone) 0.37 [ 0.31 0.41 [, 0.47 L 0.65 L, 0.69 0.67 L 0.69 0.71
33-66%(orange zone) .14 ig 1.41 latl.913 08 —8 1 �7_11.106 111=2
5-33%(green zone) 5.17 12.27 - 14.61 P 14.96 .` 18.68 1120.34 it 20.77 a 20.74 r 21.00
All values are in acres.
Table 7. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2018 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66%
reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Area of SAV Assessment Baseline Sep'18 Oct'18
Aug'18
Reference Kiln IOU0 Jig
>66%(red zone) -�
33-66%(orange zone) _ -111
5-33%(green zone) ;w7 ]
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 8

Table 8. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2019 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to
66% reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Baseline
Area of SAV Assessment Mar'19 Apr '19 May '19 Jun '19 Jul '19 Aug '19 Sep '19 Oct '19 Nov '19 Dec '19
Aug '18
Reference Eli9 ® 9 I3 L, 12 ]12 LL6 W0 118 I]16 I]17 11016
>66% (red zone) 1E2 L14 IL 13 1117 1114
33-66% (orange zone) ;4 1
5-33% (green zone) 117
Table 9. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2020 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to
66% reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Baseline
Area of SAV Assessment Apr '20 May '20 Jun '20 Jul '20 Aug '20 Sep '20 Oct '20 Nov '20 Dec '20
Aug '18
Reference ]19 _I 13 14 El 13 Mo W18 I _21 0 I 20
>66% (red zone) ; 15 _ 15 2 Nh j 321 t42_] 47 j
33-66% (orange zone) 1 m_24IU
► 336_ 41
5-33% (green zone) 5 ID2 L 28 N 11113 r 31 ! 31
*=No calculation due to coverage constraints.
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 9

Table 10. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2021 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to
66% reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Area of SAV Assessment Baseline Apr '21 May '21 Jun '21 Jul '21 Aug '21 Sep '21 Oct '21 Nov '21
Aug '18
Reference I] 19.1 1 8.2 I. 15.2 U18.9 lig5.8 IL30.3 32.7 1_31.3 t30.8
> 66% (red zone) E.9 5.6 7.1 .b 7 3 6 9 'M.1
33-66% (orange zone) 1.6 127.3 1137.4 Ihp.3 11114 MU 11110_,_5 MIV. EA_ _,
5-33% (green zone) 0.1 r4.3 C.. 9.0 U9.7 117.0 IP.3 DJ.2 W1.1 IK1.6
All values are in%of assessment area occupied by SAV.
Table 11. Total submerged aquatic vegetation (SAV) by survey month and summed for all reference areas and all wave energy reduction zones,
respectively. All values are in acres.
2018 2019 2020 2021
Referervik Total All Zones Reference Total All Zones Reference Total All Zones Reference Total All Zones
March L 0.91 13.37
April t 0.31 10.82 It 1.33 Ng 12.11 L. 0.81 .99
May 1.21 1.1113.93 g 1.36 mr .5.63 `' 1,50 .95
June � .. .. , -- --
1.63 �t6.18 1.32 W.5.27 87 51July 1 1.63 7.01 1.967.49 21
August 2.0018.06 ,. 1.7417.36 '3
September ��
October 1.73 7.14 , ' 1.99 7.39 n
1 55 6.36
18 1.94 7.59 3
November li 1.67 .1
December 1.54 Er 14.51
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 10

(1) (2) (3) (4)(5) (6) (7) (8) (9)(10)
80
70
60
OA
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8 40
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20 6I 30
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to
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�e4 cP eras � eras Ns 44 4)4 cfr ?R 4,ai lS � VO 4g 041/4' 4)4 cfrQ� 4•4k Nos Qua' 44 04'. 4)4
—v.—Reference — ,..>66%(red zone) —.-33-66%(orange zone) —_ 5-33%(green zone)
Figure 2. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2021 for each of the
wave energy reduction zones. Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave
energy; orange zone, 33 to 66% reduction;green zone 5 to 33% reduction; reference area is the surrounding area forecast to be
uninfluenced by the wave-break structure. All values are in percent cover. Data from December 2020 are not available for the green
zone or the reference area. Vertical lines and numbers correspond to Tropical Storms and Hurricanes shown in Table 2 occurring
during the SAV delineation time frame for this project.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 11

(1) (2) (3) (4) (5) (6) (7) (8) (9)(10)
80
70
60
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si*#
Reference — Combined(red+orange+green)
Figure 3. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2021 for all of the
three wave energy reduction zones combined. Combined refers to red, orange, and green which are as follows: red zone is the area
near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66% reduction;green
zone 5 to 33%; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure.All values are in
percent cover. Data from December 2020 are not available. Vertical lines and numbers correspond to Tropical Storms and
Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 12

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
80
70
N
> 60
a 50
7
r0 40
4°'''."\\
a) 30 ny
N
N T
a 20
10
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(se\ ti� ,tiO ,ti) ,.y0 ,,tics ,ti)) ti� ,tip ,tip s'iz) tioi ,.1oi 19 19 19 9 1.9 19 ti0 19 19 1%\' 1> 1> .tit 1> •'1> 1> 1>
ye" �eQ O`` �a` PQ �a� lJc ,J\ PJ� �eQ O�ti �o, Oe� PQc jai lJc ,J\ PJ� cleQ O`` �o, Oe� P. 4` ,J� ' PJ� `0 o& No,
PAP, tReference f>66%(red zone)
Figure 4. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2021 for the red
wave energy reduction zone.The red zone is the area near the wave-break structure forecast to experience a >66% reduction in
wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values are in
percent cover. Data from December 2020 are not available for the reference area. Vertical lines and numbers correspond to Tropical
Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 13

(1) (2) (3) (4)(5) (6) (7) (8) (9)(10)
80
70
› 60
v
o. 5
o. 0
v 40
v
20
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10
0
oc� 4,a§ QQ` a� No° >J� Q JQ' ye9 p 'c` ao4 Oec Q� �av v§` �J� JQ' ', o& .00 Oec PQt 4<aJ l�o NJ� N fr c, oc> N.,o4
Reference —0— 33-66%(orange zone)
Figure 5. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2021 for the
orange wave energy reduction zone. The orange zone is the area near the wave-break structure forecast to experience a 33 to
66% reduction in wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure.All
values are in percent cover. Data from December 2020 are not available for the reference area. Vertical lines and numbers
correspond to Tropical Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RKK-FL-22-81656-3676-02-REP-0I-FIN 14

(1) (2) (3) (41(5) (6) (7) (8) (9) (10)
80
70 -
a
> 60 •
v
0.
a 50
u
a'°, 40 •
30 •
20
•
10
0
, •4, '�i tio ,ti5 ~i 'N, tiO tiO tiO tiO ti O tiO LO tiO i� > �1 L>. L1 L1
� a; � c. J 4e` 4a� vc ,JPJb o`� c¢ PQt �0 J'1/4 ', 0� 0J
G O �` 4V) > N.° ', + 0
PJQ> -0-Reference -• 5-33%(green zone)
Figure 6. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through December 2021 for the green
wave energy reduction zone.The green zone is the area near the wave-break structure forecast to experience a 5 to 33% reduction
in wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values are in
percent cover. Data from December 2020 are not available for the green zone or the reference area. Vertical lines and numbers
correspond to Tropical Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 15

4.0 Conclusions
The results indicate that the wave-break structure is generally functioning as intended and as of 2021 is
facilitating a positive increase in SAV cover at a faster rate than reference areas, particularly within the
>66%and the 33 to 66% RWE reduction strata (red and orange zones) closest the wave-break structure.
This indicates that, because of the wave-break, over time 1.15 acres of seagrass were added or
preserved to contribute to ecological functions (CSA 2022, in review).
The >66% RWE reduction stratum (red zone), which is located closest to the wave-break structure and
was forecast to produce the greatest unit area effect on seagrass coalescence, showed an increase of
SAV cover every month between May and November 2021, with the exception of September, and
showed a net gain since May 2021 when compared with the baseline survey. This zone appears to have
experienced some adverse effects from proximity to the wave-break structure in 2018 due to deposition
of sediment adjacent to the structure arising from wave-break-related scouring2. These effects were
perhaps exacerbated by increased scouring during storms in the fall of 2018. Hindcasting of wave
conditions from the continually recording wave sensors placed north and south of the wave-break(CSA
2022, in review) showed a greater number of large waves on the north side of the wave-break, which
could have driven scoured sediment to the south side of the wave-break, affecting SAV abundance
during some fall storm events. Starting in about May 2020 these adverse effects appeared to have
equilibrated or lessened as SAV cover increased in most months afterwards through November 2021
(see also CSA 2022, in review).
The 33 to 66% RWE reduction stratum (orange zone) also showed an increase in SAV throughout most of
2021, although to a slightly lesser extent than the >66% RWE reduction stratum. The 33 to 66% RWE
reduction stratum showed a net gain since July 2021 when compared with the baseline (August 2018)
survey. Similar to the >66% RWE reduction stratum, the 33 to 66% RWE reduction stratum appears to
have experienced some adverse effects from proximity to the wave-break structure in 2018 and 2019.
As with the >66% RWE reduction stratum, these effects were not observed in 2020 and 2021 and
resulted in a substantial increase in SAV cover from prior years.
The 5 to 33% RWE reduction stratum (green zone), located farthest from the wave-break structure,
showed some increases in SAV cover in 2021, but less than observed in the other two RWE reduction
strata.The 5 to 33% RWE reduction stratum also did not show a substantial net gain until July 2021
when compared with the baseline survey. Unlike the other two RWE reduction strata, the 5 to 33% RWE
reduction stratum did not appear to have experienced adverse effects from proximity to the wave-break
structure, exhibiting only seasonal variation of SAV cover and returning to baseline levels in the summer
of 2019 and 2020.
The seasonal component to changes in SAV coverage was apparent in all three RWE reduction strata.
Most showed increased SAV coverage between spring and summer, followed by decreases in SAV
coverage in the fall. All three RWE reduction strata showed net positive changes in SAV acreage in spring
or summer.These changes in cover represent the seasonally detectable abundance of seagrass in
imagery.This fluctuation is normal for this area given the mix of Z. marina and H. wrightii, both of which
are at the edge of their respective geographic distributions (southernmost and northernmost,
respectively).
2 Scouring under the wave-break structure was first reported in the 19 November 2018"Summary of Year 2 Biannual Survey
—October 2018—LETTER REPORT"to NCDOT,noting that it may be impacting seagrass beds.The scouring has been a persistent
feature since 2018.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 16

With the exception of Hurricane Florence in September 2018 that likely increased scour and sediment
deposition just south of the wave-break, leading to decreased SAV cover, storm events did not appear to
have any visually discernible effect on SAV cover and total acreage.This is likely due to either storms not
being in sufficient proximity to generate damaging waves or when they were, there was often not
enough water depth to allow local wave propagation onto the shoal where the site is located.
5.0 Literature Cited
CSA Ocean Sciences Inc. 2019. UAS Survey of the Bonner Bridge SAV Mitigation Site—2018 Summary
Report. 16 pp.
CSA Ocean Sciences Inc. 2021a. UAS Survey of the Bonner Bridge SAV Mitigation Site—2019 Summary
Report. 70 pp.
CSA Ocean Sciences Inc. 2021b. UAS Survey of the Bonner Bridge SAV Mitigation Site—2020 Summary
Report. 16 pp.
CSA Ocean Sciences Inc. 2021c. Bonner Bridge Wavebreak Submerged Aquatic Vegetation Change
Analysis: 2018-2021. 21 pp.
CSA Ocean Sciences Inc. 2022 (in review). B-2500 Bonner Bridge Seagrass Mitigation Site Year 5 (2021)
Annual Survey and Project Final Report. 78 pp.
Fonseca MS, Bell SS. 1998.The influence of physical setting on seagrass landscapes near Beaufort, NC,
USA. Marine Ecology Progress Series 171:109-121.
Fonseca, MS, Kenworthy WJ, and Whitfield PE. 2000. Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biologia Marina
Mediterranea 7:373-376.
Kenworthy WJ,Zieman JC,Thayer GW. 1982. Evidence for the influence of seagrass on the benthic
nitrogen cycle in a coastal plain estuary near Beaufort, North Carolina (USA). Oecologia
54:152-158.
Malhotra A Fonseca MS. 2007. WEMo (Wave Exposure Model): Formulation, Procedures and Validation.
NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
Thayer GW, Kenworthy WJ, Fonseca MS. 1984.The Ecology of Eelgrass Meadows of the Atlantic Coast: a
Community Profile. U.S. Department of the Interior, Fish and Wildlife Service, Division of
Biological Services, Research and Development, National Coastal Ecosystems Team.
FWS/OBS-84/02. 147 pp.
CSA-RKK-FL-22-81656-3676-02-REP-01-FIN 17

UAS Survey of the Bonner Bridge SAV Mitigation Site —
2020 Summary Report
July 2021
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UAS Survey of the Bonner Bridge SAV
Mitigation Site — 2020 Summary Report
DOCUMENT NO. CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN
Internal review process
Version Date Description Prepared by: Reviewed by: Approved by:
Initial draft for
INT-01 05/21/2021 J. Pennell M. Fonseca J. Pennell
science review
INT-02 05/26/2021 TE review J. Pennell G. Dodillet J. Pennell
Client deliverable
Version Date Description Project Manager Approval
01 05/28/2021 Client deliverable J. Pennell
FIN 06/30/2021 Final deliverable M. Fonseca
FIN2 7/2021 Revised Final Pete Stafford (RKK)
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the CSA Document Production Department.

Table of Contents
Page
List of Tables iii
List of Figures iv
1.0 Background 1
2.0 Methods 1
3.0 Results and Discussion 4
3.1 ACREAGE SUMMARY 4
3.2 AUGUST 2018 (BASELINE)VERSUS 2020 SURVEYS 4
4.0 Interim Conclusions 15
5.0 Literature Cited 16
List of Tables
Table Page
1 Acreage of each of the three Representative Wave Energy(RWE) strata and
reference areas assessed from wave energy reduction modeling 3
2 Significant storm events either Tropical Storm (TS) or named Hurricanes (no
designation) for North Carolina and the dates of the first imagery obtained for this
project following the storm event 4
3 Total submerged aquatic vegetation (SAV) acreage by survey month in 2018 for each
of the wave energy reduction zones 6
4 Total submerged aquatic vegetation (SAV) acreage by survey month in 2019 for each
of the wave energy reduction zones 7
5 Total submerged aquatic vegetation (SAV)acreage by survey month in 2020 for each
of the wave energy reduction zones 7
6 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2018
for each of the wave energy reduction zones 8
7 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2019
for each of the wave energy reduction zones 8
8 Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2020
for each of the wave energy reduction zones 9
9 Total submerged aquatic vegetation (SAV) by survey month and summed for all
reference area and all wave energy reduction zones, respectively 9
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN iii

List of Figures
Figure Page
1 Overview of the Bonner Bridge wave-break submerged aquatic vegetation
monitoring program study area showing the wave-break structure, Representative
Wave Energy (RWE) reduction strata, and reference areas overlain on baseline
imagery from August 2018 2
2 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through December 2020 for each of the wave energy reduction zones 10
3 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2020 for all of the three wave energy reduction
zones combined 11
4 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through December 2020 for the red wave energy reduction zone 12
5 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through December 2020 for the orange wave energy reduction zone 13
6 Percent cover of total submerged aquatic vegetation (SAV) by survey month in
August 2018 through November 2020 for the green wave energy reduction zone 14
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN iv

1.0 Background
In response to the loss of submerged aquatic vegetation (SAV) habitat caused by the replacement of the
Herbert C. Bonner Bridge over Oregon Inlet, North Carolina, a wave-break structure was constructed
with the purpose of experimentally modifying existing, patchy SAV habitat by attenuating wave activity
to test the ability of wave reduction to promote more continuous, persistent SAV coverage. After field
surveys and wind wave modeling to guide wave-break placement,the wave-break structure was
constructed and installed between November 2016 and January 2017.
In order to evaluate effects of the wave-break structure on the potential enhancement of SAV cover, a
long-term, SAV monitoring program was established. The North Carolina Department of Transportation
(NCDOT) contracted Rummel Klepper and Kahl (RK&K) to lead this monitoring program. CSA Ocean
Sciences Inc. (CSA) was subcontracted by RK&K to support the monitoring survey design and perform
delineation of SAV cover. Data interpretations were performed from datasets collected in 2017, 2018,
and 2019, and were reported in annual summary reports (CSA, 2019; CSA, 2021).This report presents
the results of the data interpretations performed from data collected in 2020 and compares them to the
August 2018 baseline data.
2.0 Methods
The long-term SAV monitoring program for the wave-break structure includes delineation of SAV cover
from data collected multiple times per year. In 2021, it was determined that because the August 2018
data set was the first data set recorded during the seagrass growing season, it could provide a more
suitable baseline data set than the Time Zero January 2017 data set as August 2018 represents the peak
of the growing season for the visibly dominant, sub-tropical SAV, Halodule wrightii. Subsequent data
were collected in September and October of 2018, in March through December of 2019, and in April
through December of 2020.This data series will allow change analyses of SAV cover following
wave-break structure construction,which based on life history of the primary SAV species on the site
(H. wrightii, Ruppia maritima,Zostera marina) should encompass a time frame when responses by SAV
cover could occur (Kenworthy et al., 1982;Thayer et al., 1984; Fonseca and Bell, 1998).
The SAV delineation includes a forecast zone of influence (study area; where wave energy attenuation
by the wave-break is hypothesized to elicit a change in seagrass cover) adjacent to the wave-break
structure and four surrounding, haphazardly-selected 2.5-acre reference areas (Figure 1) outside of, but
immediately adjacent to,the forecast zone of influence of the wave-break structure.The reference
areas were situated to spatially bracket the forecast area of wave energy effects and were placed
without examination of their initial SAV coverage. Specifically,the study area has been organized into
the following strata based on an estimate of the potential reduction in Representative Wave Energy
(RWE; Malhotra and Fonseca, 2007)caused by the wave-break structure (Figure 1; See Table 1 for strata
acreages):
1. >66% reduction in RWE (red zone);
2. 33 to 66% reduction in RWE (orange zone);
3. 5 to 33% reduction in RWE (green zone); and
4. Reference area (forecast as having less than a 5% reduction in RWE as the result of the position of
the wave-break structure).
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 1

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Figure 1. Overview of the Bonner Bridge wave-break submerged aquatic vegetation monitoring
program study area showing the wave-break structure, Representative Wave Energy (RWE)
reduction strata, and reference areas overlain on baseline imagery from August 2018.The
wave-break structure is the black line just north of the red zone.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 2

Table 1. Acreage of each of the three Representative Wave Energy (RWE) strata and reference areas
assessed from wave energy reduction modeling.
Area of SAV Assessment Acres
Reference 9.88
>66% (red zone) polygon 0.87
33-66% (orange zone) polygon 5.16
5-33%(green zone) polygon 50.44
SAV=submerged aquatic vegetation.
Datasets were collected in January 2017 (Time Zero) by CSA, in August(baseline)through October 2018,
in March through December 2019, and in April through December 2020 by RK&K. CSA performed
interpretation of datasets for the wave-break site using GIS. SAV cover was determined by classifying
areas of SAV occurring within the study area from georeferenced, high-resolution mosaicked data sets.
Each data set had a resolution of 4 cm (1.57 in).The data was sometimes subdivided into separate
classification areas of interest (A01) based on similar pixel spectral signature ranges, often at the scale of
individual image tiles (e.g.,approximately 35 acres). Where image quality permitted, separate
classification of each AOI helped to eliminate variations in reflectance and environmental conditions
across the entire study area in order to reduce classification confusion. An unsupervised classification
was then performed on each classification A01 using a combination of iso cluster and maximum
likelihood techniques using Esri ArcGIS 10.6.1. software.
After running the unsupervised classifications, each AOI was manually interpreted by denoting visually
apparent classes of SAV and classes of non-SAV(primarily seafloor substrate). Spectral noise and holes
within the classification results were removed and corrected using a combination of Esri ArcMap
(10.8.0.)tools including Majority Filter, Region Group, Set Null (enhanced boundary edges and removed
groups of small non-contiguous pixels that were smaller than 6 pixels), and Eliminate Polygon Part
(eliminated areas that were less than 8 square feet). Lastly, a manual classification technique was then
applied to the classification with guidance from a GIS analyst experienced in SAV delineation and a SAV
biologist with extensive experience in North Carolina SAV systems.This consisted of removing areas of
over-classification (classifying non-seagrass areas as seagrass) and adding-in (digitizing) areas where
under-classification (classifying seagrass as non-seagrass) occurred, again based on visually apparent
SAV cover in the data. Comparisons of cover over time could be made against the August 2018 baseline.
SAV cover in August (mid-summer) allows comparisons for changes in marine SAV cover measured
during the growing season,which generally ranges from March through September in North Carolina
(Kenworthy et al., 1982;Thayer et al., 1984; Fonseca and Bell, 1998).Therefore, each monthly survey
could be compared to August 2018,which provided the greatest possible temporal distance among peak
growing season conditions for assessment of change in SAV cover.These comparisons captured the
seasonal dynamics of the SAV habitat. Comparisons of monthly survey data revealed general seasonal
trends of cover increase and decrease. Additional calculations were made to determine
reference-adjusted gains and losses in acreage and percent cover per month by energy zone.
At the request of NCDOT, storm events were added to figures showing change in SAV abundance over
time.Table 2 shows significant storm events (Tropical Storm and Hurricane)that have occurred during
the time of imagery acquisition for this project and the dates of the first imagery obtained for this
project following the storm event.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 3

•
Table 2. Significant storm events either Tropical Storm (TS) or named Hurricanes (no designation)for
North Carolina and the dates of the first imagery obtained for this project following the
storm event. Numbers correspond to storm events shown in figures. Values are
comparatively scaled by color palette.
Dates of first imagery
Storm Number Storm Name Year Storm Date following storm
event
1 TS Chris 2018 07/10/18 08/26/18
2 Florence 2018 09/13/18 10/02/18
3 TS Michael 2018 10/11/18 02/26/19
4 Dorian 2019 09/05/19 09/20/19
5 Humberto 2019 09/19/19 09/20/19
6 TS Arthur 2020 05/18/20 05/26/20
7 TS Fay 2020 07/09/20 07/26/20
8 Isaias 2020 08/03/20 08/10/20
3.0 Results and Discussion
3.1 ACREAGE SUMMARY
Total acreage in each zone by month is given in Tables 3,4, and 5. In 2018,the red zone (area of highest
forecast wave energy reduction) ranged from 0.31 to 0.37 acres of SAV, the orange zone (moderate
wave energy reduction) ranged from 1.90 to 2.36 acres,the green zone (lowest wave energy reduction)
ranged from 14.87 to 15.24 acres, and the reference areas ranged from 1.88 to 1.97 acres (Table 3).
In 2019,the red zone ranged from 0.11 to 0.37 acres of SAV,the orange zone ranged from 1.15 to
2.14 acres,the green zone ranged from 8.82 to 16.31 acres, and the reference areas ranged from 0.31 to
2.00 acres (Table 4).
In 2020,the red zone ranged from 0.13 to 0.41 acres of SAV,the orange zone ranged from 1.07 to
2.14 acres,the green zone ranged from 10.91 to 15.62 acres, and the reference areas ranged from
1.32 to 2.07 acres (Table 5). In December 2020,data from the reference area and the 5 to 33% RWE
reduction stratum were incomplete due to poor conditions and resultant low image quality.Therefore,
the acreage and percent cover of SAV for these two areas in December 2020 were not calculated.
3.2 AUGUST 2018 (BASELINE)VERSUS 2020 SURVEYS
Percent cover of SAV for the Bonner Bridge wave-break study area, based on the GIS classification of
prior datasets from between August 2018 (Baseline) and December 2019, can be found in Tables 6
and 7.
Percent cover of SAV for the Bonner Bridge wave-break study reference area, based on the GIS
classification of datasets from August 2018 (Baseline) was 19.1%cover. Percent cover of SAV for the
reference area between April 2020 and December 2020 ranged from 13.4%to 20.9%cover with a mean
of 17.3% (Table 8).The highest reference area cover among all surveys in 2020 was observed in
September 2020 and the lowest in June 2020.This was not unexpected based on the timing of the
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 4

surveys at the end of growing season for Halodule wrightii in late summer and the start of the growing
season in early summer, respectively.
Percent cover of SAV in August 2018 for the>66%, 33 to 66%, and 5 to 33% RWE reduction strata were
42.9%, 41.6%, and 30.1%, respectively. In 2020, percent cover of SAV for the >66% RWE reduction
stratum ranged from 14.6%to 47.4%cover with a mean of 28.6%. Percent cover of SAV for the 33 to
66% RWE reduction stratum ranged from 20.7%to 40.6%cover with a mean of 30.4%. Percent cover of
SAV for the 5 to 33% RWE reduction stratum ranged from 21.6%to 31.0%cover with a mean of 28.7%.
The changes in percent cover of SAV from August 2018 to December 2020 are plotted in Figures 2
through 6. Figure 2 shows the individual RWE reduction strata plotted against the reference areas.
Figure 3 combines the three separate RWE reduction strata into one percent cover value for each survey
and plots these values against the reference areas. Figures 4, 5, and 6 plot the change in percent cover
of SAV for each of the three RWE reduction strata (>66%, 33 to 66%, and 5 to 33% RWE, respectively).
In April 2020,the>66%and 33 to 66% RWE reduction strata showed substantially lower percent cover
values than the reference or 5 to 33% RWE reduction stratum when compared to their respective
baseline values in August 2018. From May to September 2020, percent cover of SAV within all three
RWE reduction strata and the reference area increased, as would be expected over the SAV growing
season.The >66% RWE reduction stratum showed the most consistent increase in SAV cover during this
time, with increases observed every month. From September to November 2020, percent cover of SAV
showed a general leveling off within the reference and 5 to 33% RWE reduction stratum, also in line with
what would be expected at the end of the SAV growing season. However, from June to December 2020,
percent cover of SAV within the >66%and 33 to 66% RWE reduction strata continued to increase at a
substantial rate. Unfortunately, because the December SAV cover data for the reference area and the
5 to 33% RWE reduction stratum were incomplete and not able to be utilized, it is not possible to say if
this dramatic increase in percent cover of SAV within the two RWE reduction strata closest to the
wave-break at the end of 2020 was a localized occurrence or if this increase was seen throughout the
survey area.
Comparisons of reference-adjusted gains and losses in acreage and percent cover by energy zone
showed an average monthly increase of 0.19 acres between August 2018 and November 2020.
Additionally, starting after September 2020 the percent cover of SAV within the >66%and 33 to
66% RWE reduction strata continued to increase at a substantially faster rate. Summing the
reference-adjusted monthly gains and losses over this time resulted in a net addition of 3.75 acres of
seagrass services.This indicates that over this time 3.75 acres of seagrass were added or preserved to
contribute to ecological functions. For the final report in 2021, both reference adjusted and raw non-
reference adjusted data will be utilized for comparison. A summarization of the total SAV acreage by
month for the reference areas and all RWE reduction strata combined is shown in Table 9.The total SAV
acreage in the reference zones ranged from 0.31 to 2.07 acres with a mean of 1.6 acres (standard
deviation 0.43) while the total SAV in all RWE reduction strata ranged from 10.82 to 18.06 with a mean
of 16.04 acres (standard deviation 2.01).
The influence of storm event affect on SAV abundance has not been determined. Note in Table 2, that
when storms occurred surveys were conducted within 1 month following the event, which is not enough
time for SAV seafloor to recover had there been any substantial, storm-induced reductions(except for
Tropical Storm Michael where an assessment followed the event by four months). Visual assessment of
SAV response to storm events (Figures 2 to 6) saw general decrease in SAV across zones in Spring of
2019 following storms in the fall of 2018 but that is also a period of natural SAV seasonal decline.The
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 5

project team observed that for many storm events wind drove water levels down which prevents the
introduction of wave energy onto the site.A more detailed study of wave energy and water level from
the on-site wave sensors during storm events would be needed to ascertain whether the existence of
any particular storm event had the potential to influence SAV cover as has been seen for previous storm
events in North Carolina (Fonseca et al. 2000).
Table 3. Total submerged aquatic vegetation (SAV) acreage by survey month in 2018 for each of the
wave energy reduction zones. Red zone is the area near the wave-break structure forecast to
experience a >66% reduction in wave energy; orange zone, 33 to 66% reduction; green zone
5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by
the wave-break structure. Cells with blue shading are scaled proportionally. For readability,
cells with green shading (green zone) are scaled proportionally but only for the green zone
due to their larger value range. All values are in acres.
Baseline
Area of SAV Assessment Sep'18 Oct'18
Aug'18
Reference U;M :�
>66% (red zone) El 0.37 El 0.37 © 0.31
33-66% (orange zone) 11111 _1 •
5-33% (green zone) .5.17 1&15.24 4.87
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 6

Table 4. Total submerged aquatic vegetation (SAV) acreage by survey month in 2019 for each of the wave energy reduction zones. Red zone is
the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33-66% reduction;
green zone 5-33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. Cells
with blue shading are scaled proportionally. For readability, cells with green shading(green zone) are scaled proportionally but only
for the green zone due to their larger value range.All values are in acres.
Baseline
Area of SAV Assessment Mar'19 Apr'19 May'19 Jun'19 Jul '19 Aug'19 Sep'19 Oct'19 Nov'19 Dec'19
Aug'18
Reference MIL89 I j91 ® 0.31 It3211. - 73 1.55 .
>66%(red zone) I 0.37 I 0.20 I 0.19 I 0.21 II 0.21 I 0.24 I 0.17 I 0.12 I 0.11 ;. 0.15 I 0.12
33-66%(orange zone) -1111 W1,5 I 58 M_ 1135 r_. 1111,2
5-33%(green zone) 111..17 11,11.821 t 8. 2lita.331 33] 21 p 16.31 15.63 14.90 15.59 13.13
Table 5. Total submerged aquatic vegetation (SAV) acreage by survey month in 2020 for each of the wave energy reduction zones. Red zone is
the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33-66% reduction;
green zone 5-33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. Cells
with blue shading are scaled proportionally. For readability, cells with green shading (green zone) are scaled proportionally but only
for the green zone due to their larger value range. All values are in acres.
Baseline
Area of SAV Assessment Apr'20 May'20 Jun '20 Jul '20 Aug'20 Sep'20 Oct'20 Nov'20 Dec'20
Aug'18
Reference S9 __1111116 IOLA3
>66%(red zone) II 0.37 I 0.13 I 0.13 ' 0.19 I 0.23 I 0.24 I 0.27 ® 0.28 ® 0.36 Li 0.41
33-66%(orange zone) i4-17 11104 MIK4 3r1 ' JI
�2.09 _
5-33%(green zone) 15.17 � 10.91 6_ 1.83 I -2 1 _n-, 3111 84 t53 11 15.40
*=No calculation due to coverage constraints
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 7

Table 6. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2018 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66%
reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Baseline
Area of SAV Assessment Sep '18 Oct'18
Aug'18
Reference 1111119 W119
>66% (red zone)
33-66%(orange zone) 411 A MIL37
5-33%(green zone) 11A I29]
Table 7. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2019 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66%
reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Baseline
Area of SAV Assessment Mar'19 Apr'19 May'19 Jun '19 Jul '19 Aug'19 Sep '19 Oct'19 Nov '19 Dec'19
Aug'18
Reference 1_19 11 9 I 3 © 12 1112 116 aj0 118 11116 L17 1316
>66% (red zone) 3�L132 Nj2 Iffal 1E0 ©14 •7 1114
33-66% (orange zone) ®2 ME11 1 1 O • WI
5-33% (green zone) 7 OE ® ;'I ME 126
CSA-RK&K-FL-21-81656-3676-01-REP-0I-FIN 8

Table 8. Percent cover of total submerged aquatic vegetation (SAV) by survey month in 2020 for each of the wave energy reduction zones.
Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66%
reduction; green zone 5 to 33% reduction; reference area is the surrounding area forecast to be uninfluenced by the wave-break
structure. All values are in percent cover.
Baseline
Area of SAV Assessment Apr'20 May '20 Jun '20 Jul '20 Aug'20 Sep '20 Oct'20 Nov '20 Dec'20
Aug'18
Reference ].9 Li 13 L 14 .13 0 11118 t1 Co 1320 *
>66% (red zone) 11 Ij15 IP 15 M2 W7 11E7 NO �42j __
33-66% (orange zone) 11 t1 M4 M 1 E WI
5-33% (green zone) I I2 M ii37 MI NE W4 l
*=No calculation due to coverage constraints
Table 9. Total submerged aquatic vegetation (SAV) by survey month and summed for all reference area and all wave energy reduction zones,
respectively.
2018 2019 2020
Total All Total All Total All
Reference Reference Reference
Zones Zones Zones
March 0.91 13.3j
April 0.31 10.82 1.33 12.11
May 1.21 13.93 i 1.36 15.63 _j
June 1.63 16.18 j 1.32 15.27 ]
July 1.63 17.01 _I 1.96 17.49
August 1.89 17.68 2 18.06 1.74 17.36
September 1.97 17.97 1.73 17.14 2.07 16.77 J
October 1.88 17.08 1.55 16.36 1.99 J I 17.39
November 1.67 17.18 1.94 ! I 17.59
December 1.54 14.51
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 9

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—r•Reference ->66%(red zone) —.-33-66%(orange zone) —.IP-5-33%(green zone)
Figure 2. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through December 2020 for each of the
wave energy reduction zones. Red zone is the area near the wave-break structure forecast to experience a >66% reduction in wave
energy; orange zone, 33 to 66% reduction;green zone 5 to 33% reduction; reference area is the surrounding area forecast to be
uninfluenced by the wave-break structure. All values are in percent cover. Data from December 2020 are not available for the green
zone or the reference area. Vertical lines and numbers correspond to Tropical Storms and Hurricanes shown in Table 2 occurring
during the SAV delineation time frame for this project.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 10

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Figure 3. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2020 for all of the
three wave energy reduction zones combined. Combined refers to red, orange, and green which are as follows: red zone is the area
near the wave-break structure forecast to experience a >66% reduction in wave energy; orange zone, 33 to 66% reduction; green
zone 5 to 33%; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values are in
percent cover. Data from December 2020 are not available. Vertical lines and numbers correspond to Tropical Storms and
Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 11

(5)
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Figure 4. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through December 2020 for the red
wave energy reduction zone. The red zone is the area near the wave-break structure forecast to experience a >66%reduction in
wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values are in
percent cover. Data from December 2020 are not available for the reference area. Vertical lines and numbers correspond to Tropical
Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 12

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Figure 5. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through December 2020 for the orange
wave energy reduction zone.The orange zone is the area near the wave-break structure forecast to experience a 33 to 66%
reduction in wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values
are in percent cover. Data from December 2020 are not available for the reference area. Vertical lines and numbers correspond to
Tropical Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 13

(5)
(1) (2) (3) (4) (6) (7) (8)
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. Reference -5-33%(green zone)
Figure 6. Percent cover of total submerged aquatic vegetation (SAV) by survey month in August 2018 through November 2020 for the green
wave energy reduction zone.The green zone is the area near the wave-break structure forecast to experience a 5 to 33% reduction
in wave energy; reference area is the surrounding area forecast to be uninfluenced by the wave-break structure. All values are in
percent cover. Data from December 2020 are not available for the green zone or the reference area. Vertical lines and numbers
correspond to Tropical Storms and Hurricanes shown in Table 2 occurring during the SAV delineation time frame for this project.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 14

4.0 Interim Conclusions
The results indicate that the wave-break structure is generally functioning as intended and is facilitating
a seasonally-variable, but positive, increase in SAV cover within all three RWE reduction strata,
particularly the >66% and the 33 to 66% RWE reduction strata (red and orange zones) closest the
wave-break structure.
The >66% RWE reduction stratum (red zone), which is located closest to the wave-break structure and
was forecast to produce the greatest unit area effect on seagrass coalescence, showed an increase of
SAV cover every month between May and December 2020 but only a net gain in December 2020 when
compared with the baseline survey.This zone appears to have experienced some adverse effects from
proximity to the wave-break structure in 2018 and 2019 due to deposition of sediment adjacent to the
structure arising from wave-break-related scouring'.These effects were perhaps due to increased
scouring during storms in the fall of each year. Hindcasting of wave conditions from the continually
recording wave sensors placed north and south of the wave-break will be needed to determine any
differences in wave activity over time that may be associated with SAV abundance fluctuation.
The 33 to 66% RWE reduction stratum (orange zone) also showed an increase in SAV throughout most of
2020, although to a slightly lesser extent than the >66% RWE reduction stratum.The 33 to 66% RWE
reduction stratum did not show a substantial net gain or loss when compared with the baseline survey.
Similar to the >66% RWE reduction stratum,the 33 to 66% RWE reduction stratum appears to have
experienced some adverse effects from proximity to the wave-break structure in 2018 and 2019.As with
the>66% RWE reduction stratum,these effects were not observed in 2020 and resulted in a substantial
increase in SAV cover from prior years.
•
The 5 to 33% RWE reduction stratum (green zone), located farthest from the wave-break structure,
showed some increases in SAV cover in 2020, but less than observed in the other two RWE reduction
strata.The 5 to 33% RWE reduction stratum also did not show a substantial net gain or loss when
compared with the baseline survey. Unlike the other two RWE reduction strata,the 5 to 33% RWE
reduction stratum did not appear to have experienced adverse effects from proximity to the wave-break
structure, exhibiting only seasonal variation of SAV cover and returning to baseline levels in the summer
of 2019 and 2020.
The seasonal component to changes in SAV coverage was apparent in all three RWE reduction strata.
Most showed consistent decreases in SAV coverage between the fall and spring,followed by increased
SAV coverage between spring and summer.The red and green zones showed net positive changes in
SAV acreage in November or December, which may correspond to contributions from increased biomass
for Z. marina.These changes in cover represent the seasonally detectable abundance of seagrass in
imagery. This fluctuation is normal for this area given the mix of Z. marina and H. wrightii, both of which
are at the edge of their respective geographic distributions.
1 Scouring under the wave-break structure was first reported in the 19 November 2018"Summary of Year 2 Biannual Survey—
October 2018—LETTER REPORT"to NCDOT,noting that it may be impacting seagrass beds.No clear association of the scouring
with any storm event has been observed(some storms drove water off the site resulting in little wave energy during the event).
However,the scouring has been a persistent feature since 2018.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 15

5.0 Literature Cited
CSA Ocean Sciences Inc. 2019. UAS Survey of the Bonner Bridge SAV Mitigation Site—2018 Summary
Report. 19 pp.
CSA Ocean Sciences Inc. 2021. UAS Survey of the Bonner Bridge SAV Mitigation Site—2019 Summary
Report. 76 pp.
Fonseca MS, Bell SS. 1998.The influence of physical setting on seagrass landscapes near Beaufort, NC,
USA. Mar. Ecol. Prog. Ser. 171:109-121.
Fonseca, M.S., W.J. Kenworthy, and P.E. Whitfield. 2000.Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biol. Mar. Medit. 7:373-376.
Kenworthy WJ, Zieman JC,Thayer GW. 1982. Evidence for the influence of seagrass on the benthic
nitrogen cycle in a coastal plain estuary near Beaufort, North Carolina (USA). Oecologia
54:152-158.
Malhotra, A, and Fonseca, MS. 2007. WEMo (Wave Exposure Model): Formulation, Procedures and
Validation. NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
Thayer GW, Kenworthy WJ, Fonseca MS. 1984.The ecology of eelgrass meadows of the Atlantic coast: a
community profile. U.S. Department of the Interior, Fish and Wildlife Service, Division of
Biological Services, Research and Development, National Coastal Ecosystems Team.
FWS/OBS-84/02. 147 pp.
CSA-RK&K-FL-21-81656-3676-01-REP-01-FIN 16

Brittingham, Cathy
From: Kathy Herring <[e-mail]>
Sent: Wednesday,June 16, 2021 2:23 PM
To: Sanderson, Mike; Brittingham, Cathy; Chapman, Amy; Daisey, Greg; Deaton, Anne; Lane,
Stephen; Paugh, Leilani Y; Rivenbark, Chris;Weaver, Derrick G;Williams, Paul C; Evans,
Jennifer A; Harris III, Philip S; Stanton, Tyler P; [e-mail];
[e-mail];Wilson, Travis W.; Cox, Marissa R; 'Matthews, Monte K
CIV USARMY CESAW (US)'
Cc: Pete Stafford; Kathy Herring
Subject: [External] Brief summary and slides
Attachments: 2020 Summary of Bonner SAV Mitigation.pdf; SAV_Hurricanes_Biohabitat.pptx
CAUTION: External email. Do not click links or open attachments unless you verify.Send all suspicious email as an attachment to
Report Spam.
Attached is a brief summary of the 2020 Bonner SAV Mitigation project report and a few pictures. "See"you tomorrow,
Kathy
Kathy Herring
Senior Project Scientist
RI( f[
8601 Six Forks Road
Forum 1, Suite 700
Raleigh, NC 27615
919.971.4367 C
[e-mail]
www.rkk.com
Responsive People I Creative Solutions
"RK&K"and"RK&K Engineers"are registered trade names of Rummel,Klepper&Kahl,LLP,a Maryland limited liability partnership.This message contains
confidential information intended only for the person or persons named above.If you have received this message in error,please immediately notify the
sender by return email and delete the message.Thank you.
RK&K is an equal opportunity employer that values diversity at all levels.RK&K does not discriminate in employment on the basis of race,color,religion,sex
(including pregnancy),national origin,political affiliation,sexual orientation,marital status,disability,genetic information,age,parental status,military and
veteran status,and any other characteristic protected by applicable law.Consistent with the requirements of Title VI of the Civil Rights Act of 1964,as
amended and other nondiscrimination laws and authorities,we also note that RK&K does not discriminate in its selection or retention of subcontractors on
the grounds of race,color,or national origin.We also note that RK&K will ensure that Minorities will be afforded full opportunity to submit proposals and not
be discriminated against on the grounds of race,color,or national origin in consideration for an award.
1

2/14/2022
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•
2020 Summary of Bonner SAV Mitigation
The concept of the Bonner SAV Mitigation Plan was to build a wavebreak to attenuate wave energy to
provide seagrass growing in the reduced wave energy area a better habitat in which to coalesce.
Construction of the wavebreak structure was competed in January 2017. This summer(June 2021)will
be the 5th and final year of the post construction monitoring period. A final report for the 5 year study
will be prepared and a meeting held to discuss the project in early 2022.
Surveys were conducted in August 2020(just prior to Hurricane Isaias)that included:
• Qualitative observation of conditions;
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data:
o At seagrass patch elevation rods;
o Through SEPI near-field surveys.
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for WEMo validation;
• Reporting of wave sensor data throughout the site over these and the past surveys for WEMo
validation; and
• Monitoring of epibiota sampling stations on the wavebreak structure.
Details and the results of the above can be found in the 2020 report.
In general,the structure remains stable with no further slipping of Reefmaker units. The scour pit that
formed directly under the structure remains unchanged. Sediment elevation levels within 150ft of the
south side of the structure have also remained stable since 2017. Seagrass acreage varies seasonally as
expected and also seems to be influenced by hurricanes and other major storm events.

g .„9 �, 5-AV A1►
Brittingham, Cathy
From: Kathy Herring <[e-mail]>
Sent: Monday,June 7, 2021 10:11 AM
To: Sanderson, Mike; Brittingham, Cathy;Chapman,Amy; Daisey,Greg; Deaton, Anne; Lane,
Stephen; Paugh, Leilani Y; Rivenbark, Chris;Weaver, Derrick G;Williams, Paul C; Evans,
Jennifer A;Harris III, Philip S; Stanton,Tyler P;[e-mail];
[e-mail];Wilson,Travis W.; Cox, Marissa R; Matthews, Monte K
CIV USARMY CESAW(US)
Cc: Pete Stafford; Kathy Herring
Subject [Exter B-2500 Phase 1 SAV Mitigation-Update—
Attachments: CDOT FL 21 1830 2845_BonnerBridge_Year4_FIN_12March2021.pdf
8) paE'S• 91 pc�irl .
CAUTION: External email.Do not click links or open attachments unless you verify.Send all suspicious email as an attachment to
Report Spam.
All,
As per the CAMA Permit Major Modification,issued on 12/15/15, permit condition No.21 that:"The permittee shall
conduct an annual meeting with DCM and other appropriate resource agencies to discuss and review the annual
monitoring reports and monitoring methodology for a minimum of five years after mitigation site construction." I have
attached the latest report after the summer 2020 survey for your review.
Since the BSG was not assigned a spot on the upcoming interagency agenda,and since there have been no major issues
with the structure or the Bonner Bridge SAV mitigation project,we would like to give a brief update,allowing time for
any questions,during the"Other Business" portion on the agenda for the June 17, 2021 interagency meeting. If this is
not agreeable,then we can discuss a time to schedule another meeting.
Please call me if you have any questions.
Thanks!
Kathy
Kathy Herring
Senior Project Scientist
R (,f(
8601 Six Forks Road
Forum 1, Suite 700
Raleigh, NC 27615
919.971.4367 C
[e-mail]
www.rkk.com
Responsive People I Creative Solutions
"RK&K"and"RK&K Engineers"are registered trade names of Rummel,Klepper&Kahl,LLP,a Maryland limited liability partnership.This message contains
confidential information intended only for the person or persons named above.If you have received this message in error,please immediately notify the
sender by return email and delete the message.Thank you.
RK&K is an equal opportunity employer that values diversity at all levels.RK&K does not discriminate in employment on the basis of race,color,religion,sex
(including pregnancy),national origin,political affiliation,sexual orientation,marital status,disability,genetic information,age,parental status,military and
veteran status,and any other characteristic protected by applicable law.Consistent with the requirements of Title VI of the Civil Rights Act of 1964,as
1

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B-2500 Bonner Bridge Seagrass Mitigation Site
Year 4 Annual Survey Report - 2020
March 2021
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Environmental Analysis Unit CSA Ocean Sciences Inc.
North Carolina Department of Transportation 8502 SW Kansas Avenue
1598 Mail Service Center Stuart, Florida 34997
Raleigh, North Carolina 27699-1598 . `t �1
so TRACE jPEC s�L,
CERTIFIED,,,,T.+oRizED PROVIDER

CSA
CSA Ocean Sciences Inc.
B-2500 Bonner Bridge Seagrass Mitigation Site
Year 4 Annual Survey Report - 2020
DOCUMENT NO. CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN
Internal review process
Version Date Description Prepared by: Reviewed by: Approved by:
INT-01 02/16/2021 Initial draft for E.Hodel M. Fonseca E. Hodel
science review
INT-02 02/18/2021 TE review E.Hodel K. Metzger E. Hodel
Client deliverable
Version Date Description Project Manager Approval
01 02/19/2021 Client deliverable E. Hodel
FIN 03/12/2021 Final E. Hodel
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

I
i
Table of Contents
Page
List of Tables iv
List of Figures v
List of Photos vi
1.0 Introduction 1
2.0 Methods 2
2.1 Monitoring of Relocated Seagrass 3
2.2 Areal Seagrass Cover 5
2.3 Sediment Elevation 6
2.4 Wave Regime and Model Validation 8
2.5 Epibiota Monitoring 14
3.0 Results 19
3.1 Monitoring of Relocated Seagrass 21
3.2 Areal Seagrass Cover 23
3.3 Sediment Elevation 26
3.4 Wave Regime and Model Validation 32
3.5 Epibiota Monitoring 35
4.0 Conclusions 39
5.0 References 41
Appendices 43
Appendix I Project Site Selection A-1
Appendix II Bioturbation Experiment B-1
Appendix Ill Representative Photos of Seagrasses in Planting and Reference Areas: 2016 to
2020 C-1
Appendix IV Near-Field Sediment Elevation Results: 2017 to 2020 D-1
Appendix V Representative Photos of Biota—July-August 2020 E-1
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN II/

List of Tables
Table Page
1 Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation
Site 2
2 Braun-Blanquet scale (score) and percent cover scale values (Braun-Blanquet et
al., 1972) 5
3 Total area of submerged aquatic vegetation (SAV) per wave energy reduction zone
based on GIS interpretation of monthly aerial imagery data sets of the Bonner
Bridge Seagrass Mitigation Site 26
4 One-way ANOVA testing differences in sediment elevation (ft, MLLW)from rods
installed at previous bioturbation patches between Survey 1 and subsequent
surveys 29
5 Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey 30
6 Summary statistics of the top 5%of wave heights measured at the two sensor
stations on the north and south sides of the wavebreak 32
7 Areas for the wave energy reduction zones depicted in Appendix I in both acres and
square meters 33
8 Observed wave heights in field using a wave sensor versus those predicted by
WEMo at the same station 33
9 Percent cover of biota from concrete epibiota monitoring stations during the
Baseline Monitoring Survey in January 2017 and annual monitoring surveys in May
2018, May 2019, and July-August 2020 36
10 Percent cover of biota from rock epibiota monitoring stations during the Baseline
Monitoring Survey in January 2017 and annual monitoring surveys in May 2018, •
May 2019, and July-August 2020 37
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN iv

I
List of Figures
Figure Page
1 Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site,
showing the position of the seagrass relocation planting areas,the construction
corridor, and the structure itself 4
2 Schematic (not to scale) layout of the near-field (to wavebreak) sediment elevation
transects 9
3 Area of dynamic sediment movement immediately south of the wavebreak visually
outlined in yellow 10
4 Stationary and temporary locations of the pressure sensors at the Bonner Bridge
Seagrass Mitigation Site 11
5 Epibiota monitoring stations on the wavebreak at the Bonner Bridge Seagrass
Mitigation Site 16
6 Average percent cover of total seagrass based on Braun-Blanquet scores within the
planting and reference areas for the Bonner Bridge Seagrass Mitigation Site 22
7 Baseline classification results identifying areas of seagrass (yellow) within the
Bonner Bridge Seagrass Mitigation Site for the 24 March 2017 overflight 24
8 Enlarged view of baseline aerial imagery (left) and classification results (right)
identifying areas of seagrass (yellow) within the Bonner Bridge Seagrass Mitigation
Site for the 18 April 2018 overflight 25
9 Change in sediment elevation (del_ht in ft, MLLW) over time monitored at rods
installed in previous bioturbation study 27
10 Change in sediment elevation (del_ht in ft, MLLW) over time monitored at rods
installed in previous bioturbation study 28
11 Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital
elevation model at the Bonner Bridge Seagrass Mitigation Site prior to construction
of the wavebreak(ultimate location of wavebreak shown) 31
12 Difference in hourly significant wave heights (m) between and north and south side
of the wavebreak structure for January 2017 through July 2020 34
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN v

List of Photos
Photo Page
1 The Marc Basnight Bridge, spanning over Oregon Inlet in the Outer Banks, North
Carolina 1
2 Inverted "T" shape ruler used to measure rod height above or below the substrate
at the Bonner Bridge Seagrass Mitigation Site 7
3 Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner
Bridge Seagrass Mitigation Site in June 2016 7
4 Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site 12
5 Remodeled wave sensor bracket installed in January 2018 to hold the sensor vertical
and farther away from the seabed surface 13
6 Example of numbered tag installed at every epibiota monitoring station on the
wavebreak at the Bonner Bridge Seagrass Mitigation Site 17
7 PVC camera mount framer used to photograph epibiota monitoring stations on the
wavebreak at the Bonner Bridge Seagrass Mitigation Site 17
8 Example photo of the concrete portion of an epibiota monitoring station, for
quantitative image analysis 18
9 Example photo of the rocks portion of an epibiota monitoring station,for
quantitative image analysis 18
10 Example of a stitched image of a concrete epibiota monitoring station resulting from
the modified photography method employed during the 2018 and 2020 annual
monitoring surveys due to poor underwater visibility 19
11 North-oriented view of the wavebreak installed in January 2017 at the Bonner
Bridge Seagrass Mitigation Site 39
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN vi

1.0 Introduction
The North Carolina Department of Transportation (NCDOT) contracted CSA Ocean Sciences Inc. (CSA) in
2012 (Contract No. 6300032017)to conduct in-kind seagrass (mixed Halodule wrightii, Ruppia maritima,
Zostera marina) mitigation of 1.28 acres (0.52 hectares)to compensate for losses anticipated to occur
during construction of the Marc Basnight Bridge, to replace the Herbert C. Bonner Bridge over Oregon
Inlet, North Carolina (Photo 1).The Marc Basnight Bridge provides the only highway connection for
Hatteras Island to the mainland in Dare County, North Carolina. Construction was completed and
opened to traffic in February 20191. Based on previous published research in North Carolina (Fonseca
et al., 1998, Fonseca et al., 2000, Kelly et al., 2001, Fonseca et al., 2002) CSA conceptualized creating a
wavebreak structure to modify existing, patchy seagrass habitat by attenuating wave energy to promote
more continuous, persistent seagrass coverage. This subsequent increase in seagrass acreage was
expected to meet NCDOT's seagrass mitigation requirements while enhancing ecosystem services for
the surrounding area.
.v t
1�-
Photo 1. The Marc Basnight Bridge, spanning over Oregon Inlet in the Outer Banks, North Carolina.
Image with permission from Carolina Designs, https://www.carolinadesigns.com/.
In 2012, NCDOT contracted CSA to lead the Bonner Bridge Seagrass Mitigation Site Project associated
with Project B-2500, replacement of the Bonner Bridge. From April 2015 to June 2016, pre-construction
surveys were performed. Construction of the wavebreak structure was completed in January 2017 and
entailed installation of 101 continuous Atlantic Reefmaker units in a chevron pattern oriented due
north. The Baseline Monitoring Survey (CSA, 2017) occurred immediately after construction, followed by
a series of bi-annual and annual post-construction monitoring surveys, scheduled through 2021.Table 1
summarizes the project's milestone activities and past and future monitoring events. In 2020,the Year 4
Annual Survey was conducted from 30 July to 2 August and provides the most recent data included in
this Year 4 Annual Survey Report.
1 https://www.ncdot.gov/news/press-releases/Pages/2019/2019-04-02-marc-basnight-bridge-ribbon-cutting.aspx.
Last accessed 2/1/21.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 1

Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation Experiment Initiation May 2016 Complete
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 Nov. 2016 to 18 Jan. 2017 Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan. 2017 Complete
Year 1 Biannual Monitoring Survey October 2017 Complete
Year 2 Annual Monitoring Survey May 2018 Complete
Year 2 Biannual Monitoring Survey October 2018 Complete
Year 3 Annual Monitoring Survey May 2019 Complete
Year 3 Biannual Monitoring Survey October 2019 Complete
Year 4 Annual Monitoring Survey July-August 2020 Complete
Year 5 Annual Monitoring Survey August 2021 Scheduled
USV=unmanned surface vehicle.
2.0 Methods
The Year 1 Baseline Survey included:
• Qualitative observation of conditions;
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Monitoring of selected bioturbation experiment stations (and removal of experimental mesh when
found);
• Collection of sediment elevation data at seagrass patch elevation rods;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation; and
• Maintenance of epibiota monitoring stations on the wavebreak structure.
The Year 2 and 3 Annual Surveys each included:
• Qualitative observation of conditions;
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data:
o At seagrass patch elevation rods;
o Through SEPI near-field surveys.
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for WEMo validation;
• Reporting of wave sensor data throughout the site over these and the past surveys for WEMo
validation; and
• Monitoring of epibiota sampling stations on the wavebreak structure.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 2

The Year 2 and 3 Biannual Surveys included the same data as collected during annual surveys apart from
epibiota monitoring on the wavebreak structure. Biannual surveys occurred in fall of Years 1, 2, and 3 in
the monitoring program. No additional biannual surveys will be conducted.
This Year 4 Annual Survey Report includes the same data as collected during the Year 2 and 3 Annual
Surveys, apart from collection of wave sensor data throughout the site, as enough data has been
collected from previous surveys for WEMo model validation.
CSA's methods followed the accepted monitoring plan (NCDOT, 2015) referenced in the permit (Permit
Modification No. 106-12)to ensure all monitoring requirements were met. Sections of this report that
refer to construction and engineering activities or permits originally developed using English units, will
follow the convention of reporting first in English units and then parenthetically in metric units. For the
sections of the report not directly associated with structural engineering, the convention of reporting
will be metric units followed by English units parenthetically.
Sections of the previous reports describing initial project activities, engineering, and construction have
been moved to Appendix I to focus this report on long-term post-construction monitoring. Additionally,
the description of an attempted experiment to assess the relative contribution of bioturbation (versus
wave energy)to seagrass patch maintenance has been moved to Appendix II.
2.1 MONITORING OF RELOCATED SEAGRASS
In 2016, prior to installation of the wavebreak,the State of North Carolina Department of Environmental
Quality and Coastal Resources Commission permit(Permit Modification No. 106-12) required any
seagrass within the wavebreak structure footprint and the construction corridor to be moved to the lee
side of the structure onsite. In May 2016, seagrass patches within the structure footprint and
construction corridor were relocated to two planting areas on the south side of the construction
footprint (Figure 1).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 3

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Figure 1. Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site, showing the position of the seagrass relocation
planting areas, the construction corridor, and the structure itself. Examples of randomly-selected sampling stations to assess
seagrass cover are shown for the 2020 survey within the planted areas and reference area.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 4

Percent cover of seagrass within planting areas was evaluated immediately after transplanting.
Scientists navigated to 10 pre-selected sampling stations (proportionally assigned to seven locations in
the larger eastern area and three in the smaller western area) within the planting areas using the
Trimble Geo XH GeoExplorer 2008 Series GPS.To compare the colonization of the planted areas to the
surrounding natural reference area,five additional station locations were randomly selected in the
surrounding natural area (reference area) within a 50-meter (164-foot) distance of the planting areas,
for a total of 15 sampling stations (Figure 1).
At each location, a 1-m2 (11-ft2) quadrat made of PVC was centered over each point and percent cover
of seagrass was assessed using a modified Braun-Blanquet (BB) cover and abundance technique
(Braun-Blanquet et al., 1972; Kenworthy and Schwarzchild, 1997; Fourqurean et al., 2001). Within the
quadrat, a BB scale value (Table 2) was independently evaluated for percent cover of each seagrass
species as well as total seagrass. Average BB scores were then converted to percent cover for each area
to allow interpolation of averaged BB scores that fall between BB scale values (conversion is conducted
by regressing the mid-point of percent cover associated within the range covered by each BB scale
value, on the associated BB scale value: Percent Cover=2.8108*[BB]2.2325)
Table 2. Braun-Blanquet scale (score) and percent cover scale values(Braun-Blanquet et al., 1972).
Braun-Blanquet Scale(Score) Percent Cover(%)
0.0 Not present
0.1 Solitary specimen
0.5 Few with small cover
1 Numerous, but<5
2 5 to 25
3 25 to 50
4 50 to 75
5 75to100
2.2 AREAL SEAGRASS COVER
Seagrass cover was determined by classifying areas of seagrass occurring within the Bonner Bridge
Seagrass Mitigation Site based on aerial imagery. A georeferenced, high-resolution, mosaicked aerial
image (collected by NCDOT on 18 April 2018) was used for the first classification of seagrass areas.The
aerial image was color-infrared (CIR)with a resolution of 0.08 m (0.25 ft).The image was subdivided into
separate classification areas of interest(AOI) based on similar pixel spectral signature ranges. Separate
classification of each AOI helped to eliminate variations in reflectance and environmental conditions
across the entire project area to reduce classification confusion. An unsupervised classification was then
performed on each classification AOI using a combination of iso cluster and maximum likelihood
techniques using ESRI ArcGIS 10.4 software. After running the unsupervised classifications, each AOI was
manually interpreted by denoting visually apparent classes of seagrass and classes of non-seagrass.
Spectral noise and holes within the classification results were removed and corrected using a
combination of majority filter, region group, set null (enhanced boundary edges and removed groups of
small non-contiguous pixels that were smaller than a specified value), and eliminate polygon part
(eliminated areas that were less than a specified value)tools in ArcGIS. Lastly, a manual classification
technique was then applied to the classification with guidance from a GIS analyst.This consisted of
removing areas of over-classification and adding-in (digitizing) areas where under-classification
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 5

occurred, again based on visually apparent seagrass cover. Following the 18 April 2018 overflight, no
further overflight data are being processed under this award.
2.3 SEDIMENT ELEVATION
Sediment elevation is being documented with three methods:
1. Rod Heights- measurements of sediment height relative to 2 m long rods installed during the
baseline survey to near the sediment surface in seagrass patches used for the previous,
discontinued bioturbation study;
2. USV Digital Elevation Model -a broad-scale digital elevation model created using an RTK (real-time
kinematic)-equipped unmanned surface vehicle (USV), with data collection during the baseline and
Year 5 surveys; and
3. Near-field Sediment Elevation Survey- Near-field sediment elevation measurements along
transects north and south of the wavebreak.
Rod Heights:This method (performed during all monitoring surveys)was by direct measurement of the
height of the center rod above the sediment at each of the 40 stations originally established within
seagrass patches for the bioturbation experiment (see Appendix II). At each station,the rod height
above the sediment was measured using a meter stick fastened to a piece of wood (24 cm x 5 cm x 5 cm
[18 in x 2 in x 2 in]). The 0-mark on the meter stick was attached to the center of the wood piece
creating an inverted "T" shape (Photo 2).The wood was laid flush against the seafloor to provide more
surface area to avoid the ruler sinking into the substrate.The meter stick was placed next to the rod to
obtain the measurement of the rod height above the substrate. If rods were not found, field scientists
re-navigated to the site. If rods were still not found, they were assumed buried and a small shovel was
used to dig in the immediate vicinity in attempts of finding the rod. If the rod was found,the distance
below the substrate was to be measured. If the rod was not found, it was assumed buried and no
measurement was included in the overall dataset. In addition to the 40 center rods, four additional
sediment rods (one per wave energy strata) were installed in sandy substrate and rod height above the
substrate was measured for each.
This monitoring is continuing, and updated results are provided in this report. Change in sediment
elevation among surveys and across the wave energy strata was computed for each combination of
survey times (survey 1 vs 2, 1 vs 3, 1 vs 4, 2 vs 3, 2 vs 4, etc.).The differences in change in sediment
elevation among strata for each comparison of survey times were compared in a 1-way ANOVA using
PROC GLM in SAS 9.2 after In + 10 transformation (to avoid negative numbers and address any
non-normality of the data).
USV Digital Elevation Model: A second method was employed to evaluate the entire area forecast to be
affected by the wavebreak structure. In June 2016, prior to wavebreak construction, CSA used a USV to
develop a sediment digital elevation model to collect baseline data and document future changes in
shoal elevation associated with the wavebreak installation.The USV(Photo 3) was programmed to run a
pre-selected geographic grid at 50-m (164-ft) line spacing which encompassed the entire site.
Bathymetry data was collected using dual frequency, single beam sonar at a rate of 220 to 224 kHz. A
Trimble RTK system was mounted on the USV to integrate real time navigation while the USV ran
pre-programmed grid lines (speed of approximately 9 kph [5.7 mph]).The RTK had a horizontal and
vertical accuracy of± 2 cm (±0.79 in) and real-time tidal corrections were applied to accurately
determine water levels across the site. This survey will be repeated at the end of the five-year
monitoring period in summer 2021.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 6

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Bonner Bridge Seagrass Mitigation Site.
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Photo 3. Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner Bridge
Seagrass Mitigation Site in June 2016.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 7

Near-field Sediment Elevation Survey: In June 2017, a third method of sediment elevation assessment
was initiated. SEPI Engineering Inc. (SEPI) was contracted by NCDOT to conduct high density, near-field
sediment elevation measurements in the vicinity of the wavebreak structure. North-south oriented
transects were established at five equally spaced locations, centered on, and extending north and south
of the wavebreak (Figure 2). Sediment elevations corrected to mean low low water(MLLW) were
surveyed along each transect in June 2017, September 2017, monthly from January 2018 through
December 2019,June 2020, and December 2020). In 2017, elevations at distances of 0 (at the edge of
the wavebreak structure), 5, 10, 20, 50, 75, and 100 ft were recorded. In January 2018 that changed to
increments of 5 feet out to 50 ft and then at 75 and 100 ft to improve sensitivity of detecting any
systematic change in sediment elevation near the wavebreak. Starting in June of 2018, distances of
125 and 150 ft were added to ensure elevation samples were taken beyond an apparent, newly
observed area of dynamic sediment movement immediately south of the wavebreak seen in aerial
images in spring of 2018 (Figure 3).These sediment elevation data were provided to CSA and analyzed.
Elevations were compared in a 2-way ANOVA using PROC GLM in SAS 9.2 after In + 10 transformation
(to avoid negative numbers and address any non-normality of the data). Main effects were distance
from the wavebreak and side of the wavebreak, tested at individual dates along with assessment for
interaction of main effects.
2.4 WAVE REGIME AND MODEL VALIDATION
Long Term Wave Regime: Long-term wave energy regime monitoring stations were placed at the
Bonner Bridge Seagrass Mitigation Site in "Month Year" using pressure sensor loggers to record wave
characteristics. Starting in January 2017 two pressure sensors (RBRvirtuoso models)were deployed at
stationary locations 25 m (82 ft) north and south of the wavebreak structure (Figure 4). Pressure sensors
were cylindrical and approximately 5 cm (2 in) in diameter by 25 cm (10 in) long and were mounted in a
locked casing oriented horizontally on the seafloor, approximately 15 cm (6 in) above the substrate on a
solid base, concrete-filled pillar set 0.91 m (3 ft) into the seafloor(Photo 4). Pressure sensors were set to
record bursts of pressure data every 30 minutes at a sampling rate of 4 Hz for 128 seconds.These data
also provided water level and tide documentation specifically for the site, to evaluate the wave energy
regime impinging on the north and south faces of the wavebreak structure.
In November 2017,the sensors were removed and sent back to the manufacturer (RBR)for calibration
and assessment of impacts from sand impaction and biofouling that had occurred around the wave
sensor port.This servicing caused the sensors to be out of service for approximately 2 months until their
re-deployment on 16 January 2018. Communication with RBR technical representatives indicated the
sediment impaction and biofouling had not affected the detection of wave characteristics. Nonetheless,
upon redeployment,the sensor brackets were remodeled to hold the sensors vertically with the wave
sensor port facing down (Photo 5)to minimize sand collection in the sensor port through gravity.The
sensors were re-deployed in January 2018 and have been recording continuously since that time. The
entire January 2017—July 2020 dataset has been analyzed for this report.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 8

Bonner wavebreak sediment elevation transect layout
15 sediment elevations pertransectat0,5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 125, 150 feet
15 sediment elevation locations per transect
Not to scale
Wavebreak
Pile 51
Pile 76
Pile 25
Pile 101
Pile 1
All transectsata rightangletothis red dashed baseline
Figure 2. Schematic (not to scale) layout of the near-field (to wavebreak) sediment elevation transects.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 9

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Figure 3. Area of dynamic sediment movement immediately south of the wavebreak visually outlined in yellow. Aerial image collected
18 April 2018.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 10

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C5A-NCDOT-FL-21-1830-2845-13-REP-01-FIN 11

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Photo 4. Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site.The hinged bracket is shown being
lifted; a disposable padlock is installed through the hinged piece to keep the sensor secure.
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CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 12

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Photo 5. Remodeled wave sensor bracket installed in January 2018 to hold the sensor vertical and
farther away from the seabed surface. The yellow arrow is pointing to the location of the
wave sensor port.
WEMo model validation: Model validation was developed through opportunistic sampling. During times
of onsite monitoring surveys, an RBR sensor was systematically but temporarily relocated across the site
in a grid pattern (Figure 4)to obtain a spatial assessment of predicted (WEMo computation to follow
based on water depth and wind conditions of the survey date) versus observed wave heights from the
mobile sensor. This spatial assessment was performed on 18 May 2016; 15 January 2017;
4 October 2017; 15 May 2018; 7 October 2018; 16 May 2019, and 14 October 2019 to provide a
geographically articulated assessment of wave energy distribution regarding prevailing conditions.The
relocated pressure sensor was set to record bursts of pressure data at a sampling rate of 4 Hz for
128 seconds during this sampling. During these validation data collection surveys one of the long-term
RBR sensors was used. During each survey, a scientist recorded the wind speed using a hand-held
anemometer as well as wind direction prior to sampling and again after sampling was complete. Wave
data from pressure sensors were downloaded into Ruskin software (V2.9.1) and exported to Microsoft
Excel for analysis. Analysis comprised simple univariate statistics of wind speed and predicted versus
observed regression to determine the ability of the WEMo-derived forecast to downscale to the 50 m
(164 ft) scale.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 13

2.5 EPIBIOTA MONITORING
Epibiota monitoring on the wavebreak was initiated in January 2017 through the establishment of
randomly placed, permanent monitoring stations (Figure 5). Digital photographs were recorded at each
station as a time-zero (uncolonized) baseline against which subsequent epibiota colonization (on both
rock and concrete surfaces) was compared against subsequent surveys. Stations were stratified by the
sides of the wavebreak, 30 on the north side (predicted to be exposed) and 30 on the south side, at
relative tidal (vertical) elevations related to the individual wave attenuator tier placement (high [top
tier], middle [2nd lowest tier], and low [3rd lowest tier]).Ten replicate stations were randomly assigned
per elevation strata on each side of the wavebreak for a total of 60 monitoring stations. Random
locations were selected along the wavebreak and a vertical elevation was randomly assigned to each
location. Upon establishment of the monitoring stations,scientists used the Trimble GPS to navigate to
the pre-selected random monitoring station along the wavebreak. Monitoring stations were separated
by a minimum of one Atlantic Reefmaker unit.The exact horizontal location of the monitoring station on
a wave attenuator tier was visually determined where rock placement was closest to the edge of the
concrete, making them easier to photograph. Wave attenuator tiers had a variety of rock size and
shapes embedded in the concrete, so often two adjacent, smaller rocks were selected for monitoring. To
identify the precise monitoring location and allow precise alignment for subsequent photographs, a
numbered tag was installed on the rock immediately to the right of the selected rock(s)to be monitored
(Photo 6) and alignment points for the camera framer were etched into the concrete surface.
A Sony A5000 digital camera in an underwater housing was installed on a PVC camera mount framer to
photograph the concrete and rock(s) at each monitoring station (Photo 7). The PVC frame was included
in every photo to ensure standardization of photo size (dimension of the frame was 20.3 cm x 30.5 cm
[8 in x 12 in]) (Photos 8 and 9).The standardized distance from the camera housing lens to the outer
edge of the frame was 25.7 cm (10 in).
To photograph the concrete portion of the wave attenuator tiers,the entire framer was placed flush
with the side of the concrete, so the bottom edge of the concrete was included within the frame
(Photo 8).To photograph the rock(s), the bottom of the framer was placed flush with the concrete layer
(where the selected rock was embedded) and the top of the framer rested on the concrete layer located
above the selected rock(s), which caused the framer to be tilted slightly backward (approximately
15° angle) (Photo 9).
During two of the annual surveys(2018 and 2020), all low elevation strata and some medium elevation
strata monitoring stations were entirely submerged (as opposed to being exposed) at low tide.This
coupled with sometimes high turbidity levels or wave action reduced underwater visibility to less than
one foot.As a result,the method used to photograph these stations was modified. The camera was
removed from the framer to allow capture of close-up photos within visibility limits.The framer was still
held against the concrete as described previously,yet due to the decreased distance between the
camera and the rock or concrete, multiple photographs were collected to capture the entire area within
the framer(typically four photos).The multiple photographs were then stitched together using Adobe°
Photoshop°to create a single photograph of each rock or concrete portion of the monitoring station
(Photo 10).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 14

One image of the concrete and one image of the rock(s) from each of the 60 epibiota monitoring
stations were utilized for quantitative image analysis, for a total of 120 digital images. Digital images
were processed and analyzed using Coral Point Count with Microsoft Excel extensions (CPCe)V4.1
software analysis program (Kohler and Gill, 2006). CPCe utilizes the random point count method
described by Bohnsack (1979)to accurately estimate percent cover of benthic organisms and substrate
from digital images. Because the rocks were different sizes, it was necessary to assign different numbers
of random points per image, that were proportional to the size of the rock (i.e., a larger rock would have
a greater number of random points assigned). The total area of evaluated rock was calculated for each
image using the measurement tool in CPCe. For purposes of this assessment, we assumed that all rocks
were equidistant from the camera lens. From these calculations, average rock size was determined to be
112.4 cm2 and was assigned 10 random points.The number of random points assigned to each image
was then increased or decreased proportionally to the size of the rock(s);the number of random points
for rock images ranged from four to 22. Because the area of concrete assessed was the same in each
photo, all concrete images were assigned the same number of random points (41), and points were
restricted to the area of the photograph containing only concrete. Random points were projected on
each image, and the biota or substrate located beneath each point was identified to the lowest possible
taxonomic level (for the time-zero images, no biota was detected). Data from each image were
assembled in a spreadsheet for percent cover calculations and subsequent comparative analysis.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 15

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CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 16

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Photo 6. Example of numbered tag installed at every epibiota monitoring station on the wavebreak at
the Bonner Bridge Seagrass Mitigation Site. Photo taken during the January 2017 baseline
survey.
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Photo 7. PVC camera mount framer used to photograph epibiota monitoring stations on the
wavebreak at the Bonner Bridge Seagrass Mitigation Site. Photo taken during the May 2018
survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 17

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Photo 9. Example photo of the rocks portion of an epibiota monitoring station,for quantitative image
analysis. Photo taken during the May 2019 survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 18

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Photo 10. Example of a stitched image of a concrete epibiota monitoring station resulting from the
modified photography method employed during the 2018 and 2020 annual monitoring
surveys due to poor underwater visibility. Example photos taken during the May 2018
survey.
3.0 Results
During visits to the site, scientists have consistently observed that the Bonner Bridge Seagrass Mitigation
Site is composed of patchy seagrass habitat consisting of multiple species including Z. marina,
H. wrightii, and R. maritima.Very fine silicious sand (visual observation) has consistently been the
dominant substrate type observed. Limited vessel traffic has been observed during onsite surveys within
the immediate vicinity of the wavebreak although small commercial crabbing vessels have been
observed crossing the general shoal area.
Site conditions varied during each survey and were largely driven by direction and strength of wind.
Strong northeasterly winds resulted in lowered water levels at the site and strong southwesterly winds
resulted in higher water levels. Average wind speeds during surveys have ranged from approximately
4.3 to 37.4 kph (2.6 to 21.1 mph)with maximum wind speeds ranging from 6.8 to 34 kph (4.2 to
23.6 mph)from either northeast or west and south-southwest directions. Current speeds have ranged
between 9.8 and 19.2 cm s 1,with a mean of 12.7 cm s 1. Average daily water temperatures during
monitoring surveys have ranged from 17°C(62.6°F) in springtime to 29.7°C (85.5°F) in summer.
During the October 2017 survey, scientists observed patchy seagrass habitat consisting of three species
of seagrass (Z. marina, H. wrightii, and R. maritima). H. wrightii was the most prevalent species,
followed by Z. marina and then R. maritima. The major substrate type observed throughout the site was
fine siliceous sand. Limited vessel traffic was observed during on-site surveys within the immediate
vicinity. Site conditions were relatively consistent during the survey, with slight variations due to
direction and strength of the wind. Water temperatures during the survey ranged from 22 to 23°C (72 to
73°F), with wind speeds ranging from 26.5 to 31.3 kph (16.4 to 19.5 mph), primarily out of the north.
In May 2018, scientists again observed patchy seagrass habitat consisting of the same three species of
seagrass (Z. marina, H. wrightii, R. maritima). H. wrightii and Z. marina were both commonly observed
while R. maritima was rarely observed. The major substrate type observed throughout the site was fine
siliceous sand. Limited vessel traffic was observed during on-site surveys within the immediate vicinity.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 19

•
Site conditions were relatively consistent during the survey, with slight variations due to direction and
strength of the wind. Water temperatures during the survey ranged from 23.4 to 24.8°C (74.2 to 76.7°F),
with wind speeds ranging from 7.6 to 41.1 kph (4.7 to 25.5 mph), predominantly out of the
south-southwest.
During the October 2018 survey, scientists observed patchy seagrass habitat consisting of two species of
seagrass (H. wrightii,Z. marina). H. wrightii was the most prevalent species, followed by Z. marina.
Ruppia maritima, as distinguished by presence of flowering shoots, was not observed during this survey.
The major substrate type observed throughout the site was fine siliceous sand. Limited vessel traffic was
observed within the immediate vicinity of the wavebreak. Site conditions were relatively consistent
during the survey, with slight variations due to direction and strength of the wind. Water temperatures
during the survey ranged from 25.7 to 27.4°C (78.3 to 81.3°F), with wind speeds ranging from 7.6 to
27.7 kph (4.7 to 17.2 mph), predominantly out of the east-northeast.
During the May 2019 survey, scientists observed patchy seagrass habitat consisting of three species of
seagrass (H. wrightii, R. maritima,Z. marina). H. wrightii was the most prevalent species, closely
followed by Z. marina. R. maritima was rarely observed but present.The major substrate type observed
throughout the site was fine siliceous sand. Limited vessel traffic was observed within the immediate
vicinity of the wavebreak. Site conditions were variable during the survey, depending on the direction
and strength of the wind. Water temperatures during the survey ranged from 17.0 to 19.6°C(62.6 to
67.3°F), with wind speeds ranging from 1.6 to 45.1 kph (1 to 28 mph), primarily out of the west.
During the October 2019 survey, scientists observed patchy seagrass habitat consisting of two species of
seagrass (H. wrightii, Z. marina). H. wrightii was the most prevalent species, followed by Z. marina.
R. maritima, as distinguished by presence of flowering shoots,was not observed during this survey.The
major substrate type observed throughout the site was fine siliceous sand. Water levels were high
during the survey, partially attributable to a full moon on 13 October 2019. King tides also flanked the
survey window and occurred in late September and late October in coastal areas of North Carolina due
to perigean spring tides (North Carolina King Tides Project, 20192). Site conditions varied during the
survey due to direction and strength of the wind. Water temperatures during the survey ranged from
20.2 to 22.8°C (68.4 to 73.0°F), with wind speeds ranging from 4.3 to 34.4 kph (2.6 to 21.4 mph). Wind
direction varied from southwest to south to northeast.
During the August 2020 survey, scientists observed patchy seagrass habitat consisting of three species of
seagrass (H. wrightii, R. maritima, Z. marina). H. wrightii was the most prevalent species, followed by
Z. marina. R. maritima was occasionally observed during this survey.The major substrate type observed
throughout the site was fine siliceous sand. Windy conditions several days ahead of Hurricane Isaias3
increased water levels on the final day of the survey(2 August 2020). Site conditions varied widely
during the survey from exceptionally calm to windy and rough due to direction and strength of the wind.
Water temperatures during the survey ranged from 27.5 to 29.7°C (81.5 to 85.5°F), with wind speeds
ranging from 3.9 to 42.5 kph (2.4 to 26.4 mph), primarily out of the southwest.
2 http://nckingtides.web.unc.edu/; Last accessed 5 February 2021.
3 Hurricane Isaias made landfall as a Category 1 hurricane on Ocean Isle Beach, NC on 3 August 2020.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 20

•
3.1 MONITORING OF RELOCATED SEAGRASS
Prior to construction, seagrass patches within the structure footprint and construction corridor were
relocated to two planting areas on the lee side of the wavebreak structure(Figure 1). Representative
photos of seagrasses within the planting and reference areas throughout the monitoring program are in
Appendix III. Average percent cover of seagrasses for the combined planting areas (eastern and
western)versus the reference area throughout the monitoring program are displayed in Figure 6.
In May 2016, immediately after relocation,the percent cover'of seagrass was evaluated within the
planting areas and within the surrounding reference area. Upon completion of relocation, percent cover
of seagrass was 32.7%for the relocation areas and 49.1%for the reference area (BB scores of 3.0 and
3.6, respectivelys).Transplanted seagrass within the relocation areas appeared similar to the
surrounding natural seagrass and the borders of the planting areas were visibly indistinguishable.All
seagrass blades were bright green and visibly clear of epiphytic growth.
In January 2017, immediately following construction of the wavebreak structure,the percent cover of
seagrass within the planting areas was evaluated again.The planting areas had a percent cover of
0.2%and the natural reference area had a percent cover of 7%.Therefore, seagrass cover declined by
32.5% in the planting areas and 42.1% in the reference area, indicating a substantial overall drop in
coverage. In January 2017, a brown epiphytic layer covered the majority of the visible seagrass blades
and small tufts of brown macroalgae were observed colonizing the substrate often mixed in with
seagrass. Passage of Hurricane Matthew along the North Carolina coast in October 2016 may have
contributed to the sharp decline in seagrass cover observed.
Approximately 9 months later in October 2017, no seagrass was observed in the planted areas and cover
in the reference area was approximately 62%, well above the baseline cover of 49%observed in May
2016. Seasonality in seagrass growth may be responsible for the higher cover observed in October, with
higher cover expected at the end of growing season in October versus the beginning of growing season
in May.
In May 2018, sparse seagrass was observed in the planted areas, but cover was still <1%, marking a
decrease of approximately 32%since the initial survey in May 2016. Cover in the reference area was
approximately 40%, similar to the cover observed in May 2016. In October 2018, during the biannual
monitoring survey, seagrass cover had expanded in both planted areas, with an average cover of 14.9%,
dominated by H. wrightii. Average percent cover of total seagrass in the reference area was high during
this survey at 100%,where H. wrightii was also dominant.
In May 2019, seagrasses were again present within both planting areas, but extremely sparse cover was
found in the western planting block.Average cover was only 1.7%for both planting areas and cover in
the reference area was down to 23.7% (from 100% in the previous survey). In October 2019, seagrasses
were present in both planting areas,with similar levels of cover at approximately 14%. Average cover in
in the reference area was approximately 33%.
Cover is'specific cover'as quadrats are placed only within areas colonized by seagrass(as opposed to'areal cover'which
would include any unvegetated seafloor arising from random placement of quadrats)
5 The average BB scores were converted to percent cover for each area to allow interpolation of averaged BB scores that fall
between BB scale values(conversion was conducted by regressing the mid-point of percent cover associated within the range
covered by each BB scale value,on the associated BB scale value: Percent Cover=2.8108*[BB]z.2325)
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 21

At the time of the Year 4 Annual Monitoring Survey in July-August 2020, seagrasses were present in both
planting areas; however, cover was extremely low in the eastern area which brought down the average
cover for both planting areas to 11.8%. Percent cover of total seagrass in the reference area was high at
100%.
Average Percent Cover of Total Seagrass
100.0 100.0
100
80
62.1
60 49.1 46.1
40.4
40 32.7 32.7
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20 14.0 11.81119
1 1 6.0
11
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■ Planted ■Reference
Figure 6. Average percent cover of total seagrass based on Braun-Blanquet scores within the
planting and reference areas for the Bonner Bridge Seagrass Mitigation Site.
Several factors may have contributed to the loss of seagrass within the planted areas that was initially
observed in January 2017. Seagrass was relocated to gaps within natural seagrass patches in May 2016
prior to installation of the wavebreak structure. Construction was originally scheduled for June 2016 but
delayed until November 2016 and completed in January 2017. Previous studies have shown if seagrass is
relocated to areas naturally devoid of seagrass without modifying the existing environment, natural
processes will continue to preside and the relocated seagrass should not necessarily persist
(Fonseca et al., 1998). Additionally, Hurricane Matthew passed through the Pamlico Sound and
surrounding areas on 8 and 9 October 2016, five months after seagrass relocation, prior to the
installation of the wavebreak structure. The hurricane had average wind speeds ranging from 32 to
64 kph (20 to 40 mph) with maximum wind speeds of 129 kph (80 mph) initially from the north, and
then switching direction out of the southeast as the storm passed. Severe flooding occurred along the
coast with an average rainfall of 22.1 cm (8.7 in) (http://www.weather.gov/mhx/MatthewSummary). It
is possible that the relocated seagrass had not fully established a sufficiently robust root and rhizome
system during the five months from relocation to the storm event, leaving them susceptible to erosion.
Additionally, sand accumulation on the south side of the structure due to scouring has been observed in
physical monitoring surveys and may be inhibiting seagrass survival in the immediately adjacent planted
areas.
Seagrass cover in coastal North Carolina naturally declines in winter months (Thayer et al., 1984) and
therefore lower cover was expected during the January 2017 survey. Cover in the reference area was
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 22

also very low at this time (7%), which also may have been attributable to Hurricane Matthew and/or the
sampling event occurring in winter. Since the January 2017 survey, seagrass in the planted areas has
fluctuated, and cover was <12%during the last monitoring event in July-August 2020. Seagrass cover in
the reference area has also fluctuated throughout the monitoring program (not including seasonal
fluctuations with higher cover in summer and fall surveys) but recovered since the very low cover
observed during the January 2017 survey.
With this survey, seagrass monitoring has been performed for four years post-relocation. At this point,
the dramatic fluctuation of cover among surveys in both the planting and reference areas is likely the
result of storm impacts and a highly patchy and shifting seagrass distribution. Percent cover for the
monitoring program to date, based on average BB scores, is 6.0% in the planting areas and 46.1% in the
reference area (Figure 6).
3.2 AREAL SEAGRASS COVER
The Bonner Bridge Seagrass Mitigation Site was forecast to include a total area of 301.6 acres
(122.1 hectares), and boundaries were determined by using the wave forecast model prediction.
Seagrass cover within these boundaries was determined by classifying areas of seagrass based on aerial
imagery provided by NCDOT in March 2017 (Figure 7) and April 2018 (Figure 8). Classification resulted in
33.4 acres (13.5 hectares) in March 2017 and 24.9 (10.1 hectares) in April 2018 of total seagrass cover
over the 301.6-acre (122.1-hectare)site. By visual estimation of these figures, it appears that seagrass
cover was lost in the patchy areas north and east of the wavebreak from 2017 to 2018.
In aquatic systems, classification methods for aerial imagery rarely achieve 100%accuracy.This is
because, unlike terrestrial systems, whose classification is limited primarily by atmospheric conditions,
classification of aquatic systems, especially benthic components, is limited by both atmospheric and
water conditions. Thus, accuracy of seagrass classification largely depends on water clarity and sea
surface condition at the time of imagery acquisition. Weather events affect waves on the water surface
which actively degrade visualization of the seafloor, as well as water clarity. In addition, wind events
occurring immediately prior to imagery collection may cause latent sediment suspension that negatively
impact results. Finally, many seagrass patches were interdigitated with sand and often non-contiguous,
which complicates precise delineation. In addition to atmospheric and water column effects, mosaicking
of the image produced shading gradients which interfered with seagrass classification accuracy of the
seagrass areas and appeared to be the source of most inaccuracy. An absence of ground control points
taken in association with the imagery impeded further accuracy assessment.
In both 2017 and 2018, interpretation of seagrass cover was compromised by the generally poor quality
of the imagery. Large areas of high surface reflectance and presence of white `flecks' in the imagery over
much of the AOI impaired or completely prevented interpretation of seagrass cover. Discrimination of
seagrass cover apart from sand was also difficult because of low contrast among the two habitat types.
This may have resulted from high water levels, low visibility, low sun intensity, or some combination
thereof. Upcoming utilization of low-altitude, high resolution imagery should improve seagrass cover
delineation.
Following the April 2018 overflight, no further overflight data were processed under this award.
However, aerial data sets were collected monthly beginning in August 2018 under a separate NCDOT
contract. GIS-based SAV interpretation was performed on monthly aerial imagery datasets in 2018,
2019, in addition to a previous dataset from January 2017 which was collected immediately following
construction of the wavebreak. SAV acreage per wind reduction zone and a reference zone were
tabulated for each of these monthly assessments (CSA 2018, 2019) (Table 3).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 23

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Figure 7. Baseline classification results identifying areas of seagrass (yellow) within the Bonner
Bridge Seagrass Mitigation Site for the 24 March 2017 overflight.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 24

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Figure 8. Enlarged view of baseline aerial imagery(left) and classification results (right) identifying
areas of seagrass (yellow) within the Bonner Bridge Seagrass Mitigation Site for the
18 April 2018 overflight.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 25

Table 3. Total area of submerged aquatic vegetation (SAV) per wave energy reduction zone based on
GIS interpretation of monthly aerial imagery data sets of the Bonner Bridge Seagrass
Mitigation Site.
Area of SAV Jan Aug Sep Oct March April May June July Aug Sep Oct Nov Dec
(Acres) 2017 2018 2018 2018 2019 2019 2019 2019 2019 2019 2019 2019 2019 2019
Reference 1.61 1.07 1.97 1.88 0.91 0.31 1.21 1.21 1.63 2.00 1.73 1.55 1.67 1.54
Zone
Wavebreak: 0.17 0.33 0.37 0.31 0.20 0.19 0.21 0.21 0.24 0.17 0.12 0.11 0.15 0.12
>66%
Wavebreak: 1.17 2.06 2.36 1.90 1.35 1.15 1.39 1.64 1.75 1.58 1.39 1.35 1.44 1.26
34-66%
Wavebreak: 11.63 6.41 15.24 14.87 11.82 8.82 12.33 14.33 15.02 16.31 15.63 14.90 15.59 13.13
5-33%
3.3 SEDIMENT ELEVATION
Rod Heights: Sediment elevation was monitored across the entire site by measuring the center rods at
40 seagrass patches selected for a bioturbation study(see Appendix II for description of this
since-terminated experiment) and four additional sediment rods placed in sandy substrate. These
44 rods were installed in May 2016 at locations randomly selected from within the four strata
(11 per strata) defined by the forecasted wave reduction pattern following wavebreak placement (high
wave energy reduction =>66%; moderate reduction = 34 to 66%, low reduction = 5 to 33%, and ambient
or reference =<5% reduction (Appendix Figure II-1).Across all surveys, no rods were located that were
below the sediment surface despite extensive searching and probing. If buried rods were not located,
this suggests surveys were potentially biased towards measurements indicating a lower elevation of the
sediment surface.
Change in sediment elevation was computed among the replicate rods in each of the wave energy
reduction strata among all combinations of survey dates. In lieu of survey to survey changes which
revealed no clear pattern of change over time, comparisons with the first survey time were performed
(Figures 9 and 10). A one-way ANOVA comparing changes in sediment elevations at each survey versus
that of the initial survey(Survey 1 = May 2016), by wave energy reduction strata revealed that only
comparisons among Survey 1 and Surveys 4, 6, and 7 had differences in sediment elevation among
Reference and High wave reduction zone; only Surveys 4 and 6 also had differences among the
Reference and Low and High wave reduction zones (Table 4). There has been no temporal sequence to
these differences as they have occurred in comparisons with both spring and fall surveys. However,
differences were driven by the sediment accumulation in the High wave reduction zone, closest to the
wavebreak which shows some consistency with the near-field sediment elevation surveys.A clear
pattern of sediment accumulation across wave energy strata emerged from this analysis. Sediment
accumulated most in the High wave energy reduction zone closest to the wavebreak with decreasing
sediment accumulation with decreasing wave energy reduction and distance from the wavebreak
(Figures 9 and 10).This pattern has remained consistent among the surveys, again corroborating the
near-field survey work(below).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 26

Survey 1 vs Survey 2 Survey 1 vs Survey 3 Survey 1 vs Survey 4 Survey 1 vs Survey 5
0.5• -- - 0.5, 0.5 0.5
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zone Zone Zone zone
Figure 9. Change in sediment elevation (del_ht in ft, MLLW)over time monitored at rods installed in previous bioturbation study. H= area of
high wave energy reduction by the wavebreak; M = medium; L= low; R= reference (no wave energy reduction). Error bars
represent±one standard deviation.The comparisons (e.g., 1_2, 1_3, etc. refer to comparisons among the first survey(May 2016)
and subsequent surveys.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 27

Survey 1 vs Survey 6 Survey 1 vs Survey 7 Survey 1 vs Survey 8
0.5 I 0.5- • _. _ 0.5
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zone zone zone
Figure 10. Change in sediment elevation (del_ht in ft, MLLW) over time monitored at rods installed in previous bioturbation study. H= area of
high wave energy reduction by the wavebreak; M = medium; L= low; R = reference (no wave energy reduction). Error bars
represent±one standard deviation.The comparisons (e.g., 1_6, 1_7, etc. refer to comparisons among the first survey(May 2016)
and subsequent surveys.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 28

Table 4. One-way ANOVA testing differences in sediment elevation (ft, MLLW) from rods installed at
previous bioturbation patches between Survey 1 and subsequent surveys.
Survey 1 = May 2016,Survey 2 =January 2017, Survey 3 = October 2017,
Survey 4 = May 2018, Survey 5 = October 2018, Survey 6= May 2019, Survey 7 = October
2019, Survey 8=July 2020.
Wave energy reduction Survey 1 Survey 1 Survey 1 Survey 1 Survey 1 Survey 1 Survey 1
42 43 44 45 46 47 48
Reference(none) ND ND H+ ND H+ H+ ND
Low ND ND H+ ND H+ ND ND
Medium ND ND ND ND ND ND ND
High ND ND ND ND ND ND ND
Shaded bars=significant effect at p<_0.05;comparisons with the same letters are not significantly different.ND=no significant
difference.Cells with no information represent strata where rods could not be located,presumably due to excessive sediment
deposition.R=reference, H=high wave energy reduction zone,M=medium wave energy reduction zone,L=low energy wave
reduction zone.
Near-field Sediment Elevation Survey: The surveys conducted by SEPI revealed significant scour pits
have formed under the wavebreak units themselves.This sediment is suspected to be the source of the
persistent light-colored band visible to the south of the wavebreak in aerial images (Figure 3).The
5 transects surveyed were treated as replicates for evaluating sediment elevation on both the north and
south sides of the wavebreak, by distance. A comparison of sediment elevations by distance and side of
wavebreak (north vs south) showed a generally consistent pattern of erosion in the immediate proximity
of the structure, but little change in sediment elevation with distance on either side of the wavebreak
(Appendix IV). In all cases where there was a significant difference in the sediment elevation between
the north and south sides of the wavebreak,the south side was shallower. Upon examination under
2-way ANOVA(Table 5)there was no significant interaction of the main effects (distance, side), allowing
each main effect to be re-tested independently. This statistical difference between the north and south
side of the wavebreak has been detected in 46% of the surveys.There has been no obvious temporal
pattern of when the south side was statistically different(shallower) than the north side of the
wavebreak.Therefore, while some evidence of shoaling on the south side of the wavebreak has been
detected, it is not a persistent or predictable difference which leads to the speculation that this periodic
difference may also be influenced by sand accumulation patterns operating at a larger spatial scale than
that influenced by the wavebreak. Importantly, while statistically different,the elevation differential
among the north and south side was in the range of about 6 inches. Despite being shallower,the south
side was still within the range of seagrass growth as attested by the presence of numerous seagrass
patches within this near-field survey area. During the final survey for this project in summer of 2021, a
new digital elevation model will be developed for the larger shoal environment (Figure 11). A
comparison will be made between the summer 2021 and the June 2016 survey which may shed light on
any larger scale trends in shoal elevation. But at this time the wavebreak cannot be said to have caused
a persistent, significant shallowing of the nearby shoal.
The effect of distance irrespective of side was significant (p<0.05) at every survey time. Again,
irrespective of side, significant differences were driven by the 0 distance (immediately abutting the
wavebreak) and 5-foot distances from the wavebreak which were always the deepest for every survey
(Appendix IV), reflecting the presence of the ongoing erosion pit under the structure.The ongoing(since
surveys commenced in 2017) presence of this pit indicates that the experimental wavebreak is
continually re-directing wave energy downward to the seafloor, otherwise these pits would have filled in
long ago. Future utilization of this wavebreak design should consider this effect. In this case, this
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 29

ongoing redirection of wave energy has likely negatively affected the larger project plan by adding a
mobile sand source to the location where the highest seagrass response (infilling of gaps among
seagrass patches) was forecast and may have also negatively impacted the relocated seagrass(from the
wavebreak footprint prior to construction) that was placed in the area where the sand apron
subsequently developed. Moreover,the presence of the pit under the structure has resulted in the full
suspension of the four concrete tiers composing the individual wavebreak units, above the sediment
surface; however,the structure was designed for this. While the support ring has slipped on a handful of
the units, resulting in individual wavebreak units sliding down the supporting piling,this has not
obviously influenced the wavebreak capacity of the structure nor has it resulted in any obvious
structural damage thus far. Continued, periodic inspections of the structure over time may be warranted
to ascertain its resiliency in the face of the unpredicted formation of the persistent scour pit.
Table 5. Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey. Blue
shading indicates a statistically significant(p<0.05) difference.
Year 2017 2018
Month Jun Sep Jan Feb Mar Apr May Jun
Distance <.0001 <.0001 <.0001 0.0006 <.0001 <.0001 <.0001 0.0005
Side 0.7046 0.6983 1 0.0494 0.0011 0.0372 0.0608 0.0002 0.0002
Interaction 0.8913 0.9754 0.3347 0.777 0.118 0.0744 0.4098 0.8185
Year 2018 2019
Month Jul Aug Sept Oct Nov Dec Jan Feb
Distance 0.0025 0.0022 <00006 0.0006 0.0006 0.0002 0.0022 0.0086
Side 0.0029 0.0036 0.0042 0.5273 0.1684 0.0825 0.2117 0.1080
Interaction 0.9695 0.6937 0.9016 0.8492 0.9147 0.6512 0.4738 0.9404
Year 2019
Month Mar Apr May Jun Jul Aug Sep Oct
Distance 0.0024 0.0018 0.0010 0.0059 0.0046 0.0054 0.009 0.0007
Side 0.2650 0.0151 0.0170 0.0371 0.0349 0.0154 0.2313 0.1951
Interaction 0.8691 0.8486 0.7329 0.3447 0.9921 0.6555 0.6443 0.8709
Year 2019 2020
Month Nov Dec Jun Dec
Distance 0.0005 0.005 0.0037 0.0052
Side 0.2641 0.0583 0.2639 1 0.7412
Interaction 0.7507 0.9423 0.4612 0.9923
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 30

USV Digital Elevation Model:The USV collected bathymetry data across the entire site in June 2016
(Figure 11). The survey was conducted during both flood and ebb tides and real-time tidal corrections
were made to data collected. Water depths ranged from 0.7 to 1.6 m (2.3 to 5.2 ft) across the site. The
western portion of the site was notably shallower than the eastern portion. The USV will collect
bathymetry data during the final monitoring survey in summer 2021 and data will be compared to this
baseline bathymetry.
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Figure 11. Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital elevation
model at the Bonner Bridge Seagrass Mitigation Site prior to construction of the wavebreak
(ultimate location of wavebreak shown). Soundings are in MLLW.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 31

3.4 WAVE REGIME AND MODEL VALIDATION
Long Term Wave Regime: After the wavebreak was installed, pressure sensors were installed at
specified stationary locations on both the north and south sides of the wavebreak to assess significant
wave height(highest 1/3 of waves) distribution between the two sides of the wavebreak. Figure 12
shows the difference in the average daily significant wave heights over elapsed time.Through visual
examination of the data, while there appears to be periods of time of where wave heights trend to be
higher or lower on one side or the other,the periodicity does not form any apparent seasonal
consistency. Overall,the average wave height detected on the south side of the wall was about 15%
higher than that detected on the north side and these differences are statistically significant(one-way
ANOVA, df 1, f 39.24, p<0.0001).
However, a different picture emerges when only the top 5%of wave heights (considered to be a
threshold of defining extreme events) are evaluated. Statistically,the average wave height of the top
5%of waves detected by the south-exposed sensor was significantly higher(mean of 0.20 m on the
south versus 0.13 m on the north: one-way ANOVA, df 1,f 1976.1, p< 0.0001) (Table 6). However,there
were 4,074 events where these waves were detected at the north-exposed sensor versus 814 at the
south-exposed sensor or approximately five times as many events with waves of those composing the
top 5%of all the wave heights detected on the north side of the wavebreak. Therefore, although
average, minimum, and maximum wave heights were slightly larger from the south,the number of the
largest waves was much greater from the north (and the maximum wave height of 0.44 m was still
substantive), corroborating the original expectations of what the wind field on the coast of North
Carolina might produce, which is why the forecast zone of reduction for the top 5%of wind waves was
larger on the south side of the wavebreak.
Table 6. Summary statistics of the top 5%of wave heights measured at the two sensor stations on the
north and south sides of the wavebreak.
Wavebreak Side Number of Mean Wave Minimum Wave Maximum Wave Range Wave
Observations Height(m) Height(m) Height(m) Height(m)
North 4074 0.13 0.07 0.44 0.37
South 814 0.20 0.14 0.51 0.37
WEMo model validation: Wave forecast modeling using WEMo was initially conducted in January 2016
for different lengths of the wavebreak structure. Modeling was re-analyzed in January 2017 after
installation of the 500 ft(152 m) wavebreak (Appendix I).As done previously,the model was run on
65-foot(20-meter) grid cells, as the bathymetric data which are an important driver of the calculations
was not more resolved than that distance. Forecast acreage of seagrass was computed by regression
from the relationship of wave energy to seagrass cover(Fonseca and Bell 1998).The area of the seafloor
experiencing at least a 5% reduction in wave energy was computed.The total acreage associated with
the zones of wave reduction beyond the 5%threshold is given in Table 7.Theoretically, this could result
in an overall total of 1.28 acres (0.52 hectares) of new seagrass.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 32

,
Table 7. Areas for the wave energy reduction zones depicted in Appendix I in both acres and square
meters.
Percent Representative Wave Energy Reduction Square Meters Acres
>66% 3,184 0.8
33%to 66% 21,153 5.2
5%to 33% 200,889 49.6
<5% 1,095,260 270.6
Opportunistic attempts (windy days during schedule site surveys) were also made to validate the
site-specific WEMo model forecasts at very fine spatial resolution on the shoal. One wave sensor was
unmoored from its permanent station and was utilized for WEMo model validation via systematic
relocation across the site to collect data from 24 stations both north and south of the structure
(Figure 4). WEMo computation for wave heights were made at these 24 stations and compared with
waves measured at each station.An example from one survey is shown in Table 8. In all instances, the
differences among the observed stations were very small which prevented computation of a meaningful
relationship among the predicted and observed data. Moreover, because these sampling events were
conducted within weather windows suitable for the overall survey,they occurred during relatively mild
wind events. Besides the narrow range of wind events during which surveys could be performed, the
lack of substantive changes in water depth across the site also resulted in a low variability in predicted
values. Consequently, the combination of low variability in both predicted and observed data meant the
attempt to perform a validation of the WEMo model at these times and over this small spatial extent did
not yield sufficiently diagnostic data. Previous study(Malhotra and Fonseca, 2007) demonstrated a
strong coefficient of determination (r2 ranging from 0.61 to 0.69) between predicted (by WEMo) and
observed wave heights (using continuously recording [hourly burst measurements] wave sensors) in a
study conducted over a wider range of conditions.
Table 8. Observed wave heights in field using a wave sensor versus those predicted by WEMo at the
same station.
Variable Mean Wave Height Minimum Wave Maximum Wave Range Wave Height
(m) Height(m) Height(m) (m)
Observed 0.10 0.02 0.13 0.11
Predicted 0.05 0.001 0.16 0.16
CSA-NCDOT-FL-21-1830-2845-13-REP-0I-FIN 33

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Date
Figure 12. Difference in hourly significant wave heights (m) between and north and south side of the wavebreak structure for January 2017
through July 2020. A data gap (area of straight line in 2017) arose from need to reposition and recalibrate sensors. Positive
values =wave heights higher on north side; Negative values=wave heights higher on south side.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 34

After the model was run and a smoothing technique (kriging) applied (Appendix I), a disruption
appeared in the wave reduction just south of the wavebreak. However, this was a product of the kriging
and a small zone of 33 to 66%wave reduction just south of the wavebreak was a display artifact and was
not part of the acreage calculations.
3.5 EPIBIOTA MONITORING
Water Level Observations
During the January 2017 baseline survey, ebb tides were extremely low and monitoring stations at all
three elevation strata (high, middle,and low) were exposed above water. No visibly discernible biota
had colonized the wavebreak and the percent cover of all biota was 0%.
During the next annual monitoring survey in May 2018, consistent south/southwest winds resulted in
high water levels at the wavebreak, even at ebb tide. Monitoring stations at the high elevation were
exposed above water but primarily wet and regularly splashed by waves hitting the structure during all
tidal stages observed. The middle elevation monitoring stations were exposed above water during all
tidal stages observed, also primarily wet, and regularly splashed by waves hitting the structure.The low
elevation monitoring stations were completely submerged at all tidal stages observed, even ebb tide. If
turbidity levels were high, the middle and low strata monitoring stations were photographed at a closer
distance than the high strata stations, requiring four close-up photographs per station which were later
mosaicked together.This was also required during the July-August 2020 survey.
During the May 2019 survey, ebb tides were relatively high. Monitoring stations at the high elevation
were exposed above water during all tidal stages observed but primarily wet and regularly splashed by
waves hitting the structure.The middle elevation monitoring stations were exposed above water during
ebb tides, and regularly splashed by waves hitting the structure.The low elevation monitoring stations
were completely submerged at all tidal stages observed, even ebb tide.
During the July-August 2020 survey,ebb tides were also relatively high. Monitoring stations at the high
elevation were exposed above water during all tidal stages observed but primarily wet and splashed by
waves hitting the structure during windy periods. The middle elevation monitoring stations were
partially exposed above water during ebb tides. The low elevation monitoring stations were completely
submerged at all tidal stages observed.
Epibiota Colonization
As in previous annual surveys,the percent cover of colonizing biota was assessed from photographs of
each of the 60 fixed monitoring stations along the wavebreak. Data was grouped first by substrate type
(concrete or rock),then by strata (elevations related to the individual wave attenuator tier placement;
high [top tier], middle [2"d lowest tier], and low [3rd lowest tier]), and by orientation (north or south side
of the wavebreak). Percent cover results for concrete and rock monitoring stations are displayed in
Tables 9 and 10, respectively. Representative photographs of colonized substrate and sessile and motile
fauna from the July-August 2020 survey are displayed in Appendix V.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 35

Table 9. Percent cover of biota from concrete epibiota monitoring stations during the Baseline Monitoring Survey in January 2017 and annual
monitoring surveys in May 2018, May 2019, and July-August 2020. Scaled color bars added for emphasis.
Concrete-North
Biota or Non-Living Substrate 2017 2018 2019 2020
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0 0 0 34.12 41.11 20.14 78.04 64.27 81.75 40.73 51.92 85.23
Barnacle 0 0 0 5.51 37.61 64.03 2.84 30.26 15.00 2.53 32.97 10.80
Hydroid 0 0 0 0 0 0 0 0 0 0 6.87 0
Oyster 0 0 0 0 0.58 0 0.26 1.44 2.75 0 7.69 3.69
Cyanobacteria 0 0 0 0 0 0 0 0 0 0 0 0
Non-living substrate
Concrete 100 100 100 60.37 20.7 15.83 18.86 4.03 0.50 56.74 0.55 0.28
Rock 0 0 0 0 0 0 0 0 0 0 0 0
Major categories
TOTAL BIOTA 0 0 0 39.63 79.3 84.17 81.14 95.97 99.50 43.26 99.45 99.72
TOTAL NON-LIVING SUBSTRATE 100 100 100 60.37 20.7 15.83 18.86 4.03 0.50 56.74 0.55 0.28
Concrete-South
Biota or Non-Living Substrate 2017 2018 2019 2020
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0 0 0 14.51 14.49 16.81 75.57 38.71 66.26 43.57 53.83 93.66
Barnacle 0 0 0 0 46.67 73.01 0 34.14 24.94 0 14.29 2.02
Hydroid 0 0 0 0 0 ! 6.64 0 0 0 0 4.08 0
Oyster 0 0 0 0 0 0 0 1.61 8.80 0 1.28 4.32
Cyanobacteria 0 0 0 0 0 0 0 0 0 0 0 0
Non-living substrate
Concrete 100 100 100 85.49 38.84 3.54 24.43 25.54 0 56.43 26.53 0
Rock 0 0 0 0 0 0 0 0 0 0 0 0
Major categories
TOTAL BIOTA 0 0 0 14.51 61.16 96.46 75.57 74.46 100 43.57 73.47 100
TOTAL NON-LIVING SUBSTRATE 100 100 100 85.49 38.84 3.54 24.43 25.54 0 56.43 26.53 0.00
High,Middle and Low refer to elevations related to the individual wave attenuator tier placement(high [top tier],middle[2nd lowest tier],and low[3rd lowest tier]).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 36

Table 10. Percent cover of biota from rock epibiota monitoring stations during the Baseline Monitoring Survey in January 2017 and annual
monitoring surveys in May 2018, May 2019, and July-August 2020. Scaled color bars added for emphasis.
Rock-North
Biota or Non-Living Substrate 2017 2018 2019 2020
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0 0 0 0 h 5.06 1.35 0 0 12.94 2.41 31.40 I82.09
Barnacle 0 0 0 0 ___29.11 [J 14.86 1 7 _;23.53 11.76 0 24.42 0
Hydroid 0 0 0 0 0 0 0 0 0 0 0 0
Oyster 0 0 0 0 0 0 0 B 7.84 III 18.82 0 11.63 L 16.42
Cyanobacteria 0 0 0 0 0 0 0 I 4.9 Li4.13 0 0 0
Non-living substrate
Concrete 0 0 0 0 0 0 7 I 3.93 0 20.48 0 1 1.49
Rock 100 100 100 100 65.82 83.78 93 a. 59.8 22.35 77.11 32.56 0
Major categories
TOTAL BIOTA 0 0 0 0 34.17 16.21 7 36.2/ 77.65 I 2.41 67_44 98.51
TOTAL NON-LIVING SUBSTRATE 100 100 100 100 65.82 83.78 100 63.73 22.35 .97.59 32.56 ! 1.49
Rock-South
Biota or Non-Living Substrate 2017 2018 2019 2020
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0 0 0 0 0 1.41 0 16.09 53.66 0 84.72 75.68
Barnacle 0 0 0 0 I 3.51 16.9 0 4.6 24.39 0 9.72 0
Hydroid 0 0 0 0 0 I 0 0 0 0 0 0 0
Oyster 0 0 0 0 0 0 0 2.3 ® 13.41 0 0 21.62
Cyanobacteria 0 0 0 0 0 0 0 0 0 0 0 0
Non-living substrate
Concrete 0 0 0 0 0 0 I 3.06 lj 6.9 0 IL 18.29 1.39 I 2.70
Rock 100 100 100 100 ;,_96.49 81.169] 1.194 I W70.1 j [j 8.54 11.1tni. I 4.17 0
Major categories
TOTAL BIOTA 0 0 0 0 I 3.51 18.31 0 122.99 Ink.46 I 0 4.44 j ..30 I
TOTAL NON-LIVING SUBSTRATE 100 gum 100 _J I 100 96.49 81.69 i Mik-IIIIP;:.01.1 U 8.54 l 0 5.56 .I 2.70
High,Middle and Low refer to elevations related to the individual wave attenuator tier placement(high[top tier],middle[2nd lowest tier],and low[3rd lowest tier]).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 37

Colonizing biota observed on concrete substrate included barnacles, macroalgae (primarily unidentified
green hair algae), hydroids, and oysters (Table 9). For concrete stations, biotic colonization was
dominated by barnacles in 2018 followed by macroalgae in 2019 and 2020 for most strata. Percent
cover of barnacles declined from 2018 to 2020, particularly in the low strata. Percent cover of
macroalgae increased for all strata in 2019, then became more variable in cover, showing some
decreases and increases depending on strata in 2020. In 2018, hydroids were only present on south side
low strata (6.6%cover), not observed in 2019, and observed in low cover(<_6.9%) on middle strata only
(both north and south sides) in 2020.To date, oysters have had no appreciable cover on the high strata,
and middle and low strata showed no appreciable cover until 2019. In 2019 and 2020, oyster cover
gradually increased on middle and low strata on the north side yet decreased for these strata on the
south side. The highest oyster cover(8.8%) thus far on concrete was found in 2019 on low strata on the
south side.
Colonizing biota on rock substrate to date includes macroalgae, barnacles, oysters, and cyanobacteria;
no hydroids have been observed (Table 10). For rock stations, biotic colonization was dominated by
barnacles on both sides of the structure in 2018. However, in 2019 macroalgae or oysters were
dominant depending on strata. In 2020, macroalgae was the dominant biota among all strata and sides
of the structure. Oysters on rock substrate were first recorded during the 2019 survey on middle and
low strata and cover has generally increased within these strata from 2019 to 2020. However, oysters
have not been observed on high strata throughout the monitoring program. A pulse of cyanobacteria
was present on the north side middle and low elevation strata in 2019. In 2020,the veined rapa whelk
(rapana venosa) along with egg masses (Appendix V, Photo V-2) were observed on one portion of the
wavebreak. Upon further investigation, it was learned that this species is considered invasive in the
Chesapeake Bay(Mann et al., 2006). Further observations will be made during the next survey to gather
more quantitative data relative to its distribution and abundance on the structure.
In 2020, epibiotic cover on the low elevation strata was nearly 100%for both rock and concrete
surfaces, irrespective of side of the structure. Middle elevation strata also showed high cover, lagging
slightly behind the low strata. High elevation strata continued to show the least cover. For all elevation
strata, concrete exhibited greater total colonization by biota versus rock on both north and south sides
of the structure. Concrete typically exhibited greater colonization by macroalgae and fauna than the
rock substrate, while oysters have shown greater affinity for the rock substrate. While a clear trend of
increased colonization has occurred, there were non-systematic fluctuations in cover among year, side,
and elevation strata,which is not uncommon for sessile intertidal communities.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 38

4.0 Conclusions
The wavebreak was successfully installed in January 2017 (Photo 11) and passed its post-construction
engineering inspection. Monitoring will continue for an additional year, through 2021 (Table 1) which
will build from this report.
Photo 11. North-oriented view of the wavebreak installed in January 2017 at the Bonner Bridge
Seagrass Mitigation Site.The total structure length is 500 ft (152 m).
Seagrasses were successfully relocated from the construction corridor to two planting zones south of
the wavebreak footprint in May 2016. Seagrasses in the area are composed of all three of the marine
species found in North Carolina (mixed H. wrightii, R. maritima,Z. marina). Seagrass cover measured
within the confines of natural, colonized seagrass displayed a large increase from May 2016 to
July-August 2020 (+51%).The planted seagrass area showed a decrease of-21%during this same
timeframe. The increased cover observed in the natural area may partially be the result of sampling
early(May)versus late (August) in the growing season. As for the planting areas, Hurricane Matthew in
October 2016 likely impacted newly relocated seagrasses. The hurricane passed over the mitigation site
prior to the installation of the wavebreak structure; thus,the relocated area was highly exposed to an
extreme wave event only 5 months after planting which could have led to disruption of the relocated
material. In October of 2017, no seagrass was found in the randomly selected sampling stations from
both planting areas. Subsequent surveys found cover ranging from 0.7 to 14.9% in the planted areas
while during the same time, cover in the reference area ranged from 23.7 to 100%cover. At this point,
the low cover among surveys in the planted areas is likely the result of sand deposition on the
immediate south side of the wavebreak arising from sand being mobilized from under the structure,
which could be impeding seagrass colonization.The variable cover observed in the reference area is
likely the result of storm impacts and a highly patchy and shifting seagrass distribution. Percent cover
has thus far averaged 6.0% in the planted areas and 46.1% in the reference area.
A bioturbation experiment to help determine the relative role of bioturbation versus wave energy
reduction in seagrass space occupation was significantly disrupted by unknown sources. Only 20% of the
mesh (8 out of 40 remesh sheets) was relocated during the January 2017 survey.The wavebreak was not
present during this time so comparisons could only be tested among the remaining 8 remesh sheets and
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 39

those edges that did not receive remesh.There was no significant difference (p<0.05) among the
change in seagrass patch diameter between the remesh and no remesh treatments, preliminarily
indicating that bioturbation was not strongly influencing the expansion of patch margins at that time.
However, the passage of Hurricane Matthew may have obscured effects (disturbance effects like
Hurricane Matthew erode seagrass patches from their edge, much like sting ray bioturbation [Fonseca
et al., 2000]).
Physical data collection of sediment elevation and wave energy has been completed from 2016 through
2020.A digital elevation model (DEM) of the site was collected using the USV in June 2016 and these
data will be compared with a final DEM survey in summer 2021 to determine net sediment
accumulation or loss in the project area. Sediment elevation rods will also continue to be monitored to
gain an understanding of short-term fluctuations in sediment elevation.A clear pattern of sediment
accumulation across wave energy strata emerged from this analysis. Sediment accumulated most in the
High wave energy reduction zone closest to the wavebreak with decreasing sediment accumulation with
decreasing wave energy reduction and distance from the wavebreak.
More detailed monitoring of the near-field sediment elevation (within 150 feet) and the far-field (spread
over the entire wave energy forecast area) has shown a stable profile over time. With the near-field
monitoring,the south side has consistently been approximately 0.5 ft shallower than the north but still
within the range of colonization by seagrass, as is evidenced by the continued presence of seagrass in
this area, including the planting and reference areas.
The final wave modeling effort indicated that theoretically,the wavebreak influence on seagrass cover
could result in a total of 1.28 acres (0.52 hectares) of new seagrass overall.Aerial imagery was collected
by NCDOT in March 2017 and April 2018.That collection was terminated in April 2018 and replaced by
monthly surveys under another contract. GIS-based SAV interpretation was performed on the monthly
aerial imagery datasets in 2018, 2019, in addition to a previous dataset from January 2017 which was
collected immediately following construction of the wavebreak. SAV acreage per wind reduction zone
and a reference zone were tabulated for each of these monthly assessments to capture changes in
seagrass cover at the Bonner Bridge Seagrass Mitigation Site (CSA 2018, 2019).
Assessment of epibiotic colonization has occurred annually using a stratified random, repeated
measures design. Photographs of the exact locations on the structures, stratified by relative tidal
elevation and north and south sides of the wall have been repeated over time to quantify epibiotic
colonization trajectory, abundance, and composition. As expected, there was no discernible epibiotic
colonization during the Baseline Survey in January 2017.At the time of the May 2018 survey,
colonization of the structure was apparent, primarily by macroalgae and barnacles.To date, a clear
trend of increasing colonization continues with high levels of colonization among all elevations of the
wavebreak structure, irrespective of side (north or south facing). In 2020,the most frequently observed
biotic cover on concrete and rock substrates was macroalgae. Concrete typically exhibited greater
colonization by macroalgae and fauna than the rock substrate,while oysters have shown greater affinity
for the rock substrate. In 2020, epibiotic cover on the low elevation strata was nearly 100%for both rock
and concrete surfaces, irrespective of side of the structure. Middle elevation strata also showed high
coverage, lagging slightly behind the low strata. High elevation strata continued to show the least cover.
Non-systematic fluctuations in cover among year, side, and elevation strata have been observed, which
is not uncommon for sessile intertidal communities.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 40

5.0 References
Bohnsack,J.A. 1979. Photographic quantitative sampling of hard-bottom benthic communities. Bulletin
of Marine Science 29:242-252.
https://www.researchgate.net/publication/233545259 Photographic Quantitative Sampling o
f Hard-Bottom Benthic Communities
Braun-Blanquet,J., G.D. Fuller and H.S. Conrad. 1972. Plant Sociology:the Study of Plant Communities.
Hafner. New York, NY. https://archive.org/details/plantsociologyst00brau
CSA Ocean Sciences Inc. (CSA). 2017. B-2500 Bonner Bridge Seagrass Mitigation Site: Baseline
Monitoring Survey Report. Prepared for North Carolina Department of Transportation, Natural
Environment Section. 38 pp.
CSA Ocean Sciences Inc. (CSA). 2018. UAS Photogrammetry of the Bonner Bridge SAV Mitigation Site—
2018 Summary Report. Prepared for Rummel Klepper& Kahl, 16 pp.
CSA Ocean Sciences Inc. (CSA). 2019. UAS Photogrammetry of the Bonner Bridge SAV Mitigation Site—
2019 Summary Report. Prepared for Rummel Klepper& Kahl, 70 pp.
Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near Beaufort,
NC, USA. Marine Ecology Progress Series 171:109-121. https://www.int-
res.com/articles/meps/171/m171p109.pdf
Fonseca, M.S.,W.J. Kenworthy, and G.W.Thayer. 1998. Guidelines for the Conservation and Restoration
of Seagrass in the United States and Adjacent Waters. NOAA COP/Decision Analysis Series.
222 pp. http://aquaticcommons.org/14649/1/das12.pdf
Fonseca, M.S., W.J. Kenworthy, and P.E. Whitfield. 2000. Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biologia Marina
Mediterranea 7:373-376.
Fonseca, M.S., P.E. Whitfield, N.M. Kelly, and S.S. Bell. 2002. Modeling seagrass landscape pattern and
associated ecological attributes. Ecological Applications 12:218-237.
https://www.researchgate.net/publication/228827676_Modeling_Seagrass_Landscape_Pattern
_and_Associated_Ecological_Attributes
Fourqurean,J.W., A. Willsie, and C.D. Rose. 2001. Spatial and temporal pattern in seagrass community
composition and productivity in south Florida. Marine Biology 138:341-354.
http://seagrass.fiu.edu/resources/publications/Reprints/Fourqurean%20et%20a1%202001%20M
arine%20Biology.PDF
Kelly, N.M., M.S. Fonseca, and P.E. Whitfield. 2001. Predictive mapping for management of seagrass
beds.Aquatic Conservation Marine and Freshwater Ecosystems 11:437-451.
Kenworthy, W.J. and A. Schwarzchild. 1997.Vertical growth and short shoot demography in Syringodium
filiforme in outer Florida Bay, USA. Marine Ecology Progress Series 173:25-37. https://www.int-
res.com/articles/meps/173/m173p025.pdf
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 41

Kohler, K.E. and S.M. Gill. 2006. Coral Point Count with Excel extensions(CPCe): A Visual Basic program
for the determination of coral and substrate coverage using random point count methodology.
Computers and Geosciences 32(9):1,259-1,269.
Malhotra, A. and M.S. Fonseca. 2007. WEMo (Wave Exposure Model): Formulation, Procedures and
Validation. NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
https://repository.library.noaa.gov/view/noaa/9331
Mann, R., J.M. Harding, and E. Westcott. 2006. Occurrence of imposex and seasonal patterns of
gametogenesis in the invading veined rapa whelk Rapana venosa from Chesapeake Bay, USA.
Marine Ecology Progress Series 310: 129-138.
North Carolina Department of Transportation. 2015. STIP B-2500 Bonner Bridge Phase I SAV Mitigation
Plan, Pamlico Sound, Oregon Inlet Dare County, North Carolina. 9 pp. +apps.
Thayer, G.W., W.J. Kenworthy and M.S. Fonseca 1984. The Ecology of Eelgrass Meadows of the Atlantic
Coast: A CommunityProfile. U.S. Fish and Wildlife Service. FWS/OBS-84/02.
https://digitalmedia.fws.gov/digital/collection/document/id/1732/
Townsend, E. and M.S. Fonseca. 1998.The influence of bioturbation on seagrass landscape patterns.
Marine Ecology Progress Series 169:123-132. https://www.int-
res.com/articles/meps/169/m169p123.pdf
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 42

Appendix I
Project Site Selection
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 1-1

In 2015, CSA completed the process of site selection ([Report] Table 1). Existing seagrass cover and site
conditions were compared between potential mitigation sites within the Pamlico Sound in the vicinity
(".8 km [^'5 mi]) of the Oregon Inlet.The Bonner Bridge Seagrass Mitigation Site was identified on a
historically stable shoal, where seagrass growth was evident, and had the most potential for increased
seagrass cover with gap closure among existing patches of the sites examined.The site was located near
dredge spoil islands approximately 4.8 km (3 mi) southwest of the existing Bonner Bridge at Oregon
Inlet. Wave and seagrass response models were utilized to determine the length of the wavebreak
forecast to achieve the 1.28 acres (0.52 hectares) of seagrass mitigation.
Also, in 2015, CSA completed development of the wavebreak design and placement, a task which
required both wave forecasting,seagrass recovery forecasting and engineering sub consultation for
placement of the structure design. Wave forecast modeling (Malhotra and Fonseca, 2007) was utilized
to estimate the wave reduction effects of the wavebreak structure. Percent wave reduction was
computed from comparisons of no-wavebreak and wavebreak modeling scenarios for various length
wavebreak structures. The percent wave energy reduction for a given length wavebreak was converted
to percent seagrass cover(recomputed from Fonseca and Bell, 1998) to predict the overall increase in
seagrass acreage across the site as the result of wave reduction.The 500-foot (152-meter) long wall was
designed with an inverted "V-shape"consisting of two 250-foot (76.2-meter) sections.
The V-shape was a professional judgement on the part of the design team to mitigate wave impacts on
the wall from the forecast direction of maximum wave height development (northerly).Thus,the
wavebreak was oriented on the site to attenuate the dominant north and northeasterly exceedance
event (wind events composing the local top 5%of all hourly wind speeds, along with their direction,
over the preceding three years period) winds and create a calmer environment on the lee side (south
facing side) of the structure to promote seagrass patch coalescence and new, permanent seagrass
acreage.
Once the 500-foot (152-meter) wall length was selected by NCDOT (the wall length that most closely
approximated the forecast 1.28 acres [0.52 hectares] of new seagrass cover), four wave energy regimes
(treatments)were defined from a cumulative frequency analysis of the area covered by the modeling
effort where greater than 5%energy reduction was forecast to occur as the result of the wavebreak
(Figure I-1). The wave energy regimes represent high wave energy reduction (>66%forecast reduction),
moderate reduction (34 to 66%), low reduction (5 to 33%), and ambient or reference (<5% reduction).
These wave energy reduction regimes became strata for random selection of various sampling described
below.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN I-1

•
75°35'317W 75°3520"W 75°35'10'W 75°35'0"W
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500ft Wavebreak Structure
Percent RWE Reduction
>66% •
33%-66%
5%-33%
-<5%
75'35'30"W 75'35'20'W 75°35'17W 75°35'0'W 75'34'50 W
0 100 200 400 Meters
-.. .4** I 1 $ I I I I I0
CS A Coordinate System:WGS 1984 UTM Zone 18N
Figure I-1. Post-construction forecast of wave energy(RWE; representative wave energy [J m-1 wave
crest]) based on 500-foot (152-meter) wavebreak structure, superimposed on image of
seagrass cover.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 1-2

Project Engineering and Design
CSA subcontracted SEPI Engineering to design the wavebreak and provide the engineering Signed and
Sealed Design Plans. The wavebreak was designed based on wave height forecasts provided by CSA
using the WEMo model (Malhotra and Fonseca, 2007) and the aforementioned exceedance event winds.
To meet the 500-foot (152-meter) design length,the structure was composed of 101 individual "Atlantic
Reefmaker" units each containing a central piling, one concrete base unit, and three concrete wave
attenuator units stacked on the base unit and each embedded with natural granite rock to increase
surface area for epibiota colonization (each unit was 4.8 ft x 4.8 ft x 4 ft [1.46 m x 1.46 m x 1.22 m])
(Photos I-1 and 1-2). Granite rock was chosen to prevent bioerosion of the enhanced surface area. Each
unit had a bottom clamp and a top collar installed to secure the concrete layers to the central piling to
hold the base and wave attenuator tiers in a fixed vertical position on the piling, preventing settling into
the sand substrate over time.
6 , �,.
I
ti.\
s \-- ...... r .
r
K
r.` rt
r cam _ t.. ' K -.a � . ^IjR
4
Photo I-1. East-facing view of installation of the central pilings with piling clamps at the Bonner
Bridge Seagrass Mitigation Site. Yellow arrow points to an installed clamp.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 1-3

•
y'.
1' .. r�� 'r►li.,. ',`rnz. �^-..ter. -
31
... i '
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-
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rt
Photo 1-2. One Atlantic Reefmaker unit consisting of one base unit on the bottom and three wave
attenuator tiers containing granite rock. One hundred and one of these units were
installed at the Bonner Bridge Seagrass Mitigation Site. For scale, the width of the units is
4.8 ft (1.46 m).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 1-4

To evaluate the influence of biological disturbance on seagrass patches at the site (sensu Townsend and
Fonseca, 1998), CSA installed a bioturbation exclusion experiment in May 2016. There, 40 locations were
randomly selected from within strata (10 per strata) defined by the forecasted wave reduction pattern
following wavebreak placement (high wave energy reduction =>66%; moderate reduction = 34 to 66%,
low reduction = 5 to 33%, and ambient or reference=<5% reduction) (Figure II-1). The nearest isolated
seagrass patch to that location was then selected for application of the experimental treatment.At the
center of all 40 patches, a 2.4-meter(8-foot) long stainless-steel rod (Photo II-1) was driven into the
sediment until only 3 to 10 cm (1 to 4 in) remained above the sediment. Five randomly selected patches
were assigned wire mesh (wire remesh panels 1.07 m x 2.13 m [42 in x 84 in]) welded steel wire remesh
sheet (with 0.106 m x 0.1.06 m [4 in x 4 in] mesh size)to exclude bioturbating sting rays and five were
un-protected within each of the four wave energy regimes (total of 40 patches). At each of two
randomly selected cardinal directions per patch,the distance from the center rod to the edge of the
seagrass was measured in centimeters using a metric tape (Photo 11-2). For patches receiving mesh, each
of the cardinal directions received a wire mesh.The longest length of the mesh was positioned parallel
to the patch edge approximately 1/3 on seagrass and 2/3 on sand to allow room for seagrass growth
(Photo II-3).Two 1-shaped rebar stakes 0.3 m (1 ft) long anchored the mesh, so it was flush on the
seafloor. Flush deployment on the seafloor and anchoring were performed to prevent entanglement by
sea life, such as diving birds. Other information recorded for each patch included the treatment received
(mesh or no mesh), elevation of the rod above the sediment, and seagrass species observed at each
edge. Change in the distance from the center rod to the patch margin will be recorded over time.The
statistical approach for this experiment is a repeated measures two-way analysis of variance with wave
energy and patch protection as main effects.The mesh and stakes will be removed and disposed of
appropriately when patch coalescence begins, at which time monitoring of these patches will cease.
During the May 2018 survey, scientists revisited each patch to collect data. Scientists navigated to the
location of the center rod using the Trimble GPS. Once on location,they searched for the center rod
using a glass bottom bucket and grazing a rake (tines up)on the seafloor.The distance from the center
rod to the edge of the seagrass patch was re-measured along the same cardinal directions established
during installation.The presence or absence of mesh, elevation of the rod above the sediment, and
seagrass species observed at each edge was also noted for each patch.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 11-1

\\T„scriampfiA
I
\\.
40,
‘\ ‘‘, ,,,„\
Photo II-1. Center rods (2.4 m [8 ft]) installed in May 2016 at each bioturbation experiment seagrass
patch within the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 11-2

_T
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Photo 11-2. S measuring from to theagrass
randomly cientists selected directionthe at the center Bonnerrod Bridgee edge Seagrassofthe Mitigations patch Site. on the
I
' 8 t
'k iy '
Photo 11-3. Exclusion mesh installed flush on the seafloor on the edge of the seagrass patch within the
Bonner Bridge Seagrass Mitigation Site. Mesh size is 0.106 m •x 0.1.06 m (4 in x 4 in).
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN II-4

Bioturbation Experiment
At the time of setting out the experiment in May 2016, the average distance from the center rod to the
edge of all 40 patches was 3.8 m (12.5 ft) (Table II-1). At the onset of the experiment patches with
exclusion mesh had an average distance of 3.9 m (12.8 ft) and patches without exclusion mesh had an
average distance of 3.7 m (12.1 ft).
Table II-1. Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment. Updated July 2018; n/a = not applicable; meshes had been
removed. ND = no data; distances not measured as experiment had ended.
Patches with Patches without
Survey All 40 patches(m) exclusion mesh(m) exclusion mesh (m)
May 2016 3.8 3.9 3.7
January 2017 3.5 3.7 3.3
October 2017 1.48 n/a n/a
May 2018 ND ND ND
In January 2017, all 40 bioturbation patches were revisited and monitored. For all 40 patches,the
average distance from the center rod to the edge of the patch was 3.5 m (11.5 ft). For all mesh
treatment patches,the average distance to the edge of the patch was 3.7 m (12.1 ft) (however, mesh
was only located at 8 locations within 7 patches at the time of the survey). Patches without exclusion
mesh had an average distance of 3.3 m (10.8 ft). In October 2017,the number of monitored patches was
reduced to 14 to revisit only those 7 patches that still contained mesh at the time of the January survey
in addition to an equal number of non-mesh patches (n=7). Average distance from the center rod to the
edge of all 14 monitored seagrass patches was 1.5 m (4.9 ft). For the 7 patches that contained mesh at
the time of the January survey,the average distance to the edge of the patch was 0.5 m (1.6 ft).The
7 patches without exclusion mesh had an average distance of 1.9 m (6.2 ft). In October 2017,the
experiment had been terminated and only the distance to patch edges were measured.That distance
had reduced from 3.5 to 1.48 m suggesting the dynamic nature of seagrass patch margins in this area.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 11-5

Appendix Ill
Representative Photos of Seagrasses in Planting and Reference Areas: 2016 to 2020
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 111-1

aa..
Ib.
,�• - ..� . ,*'-i:.` ,..4
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1i 411,
a Nei
*1-414
Photo III-1. Transplanted seagrass with clean blades appearing similar to surrounding natural seagrass
during the May 2016 survey.
31.
Photo III-2. Natural seagrass in the reference area showing blades covered with a layer of epiphytes
during the January 2017 baseline survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 111-2

144 Q q 1 �.
14,
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.
Photo III-3. Natural seagrass in the reference area during the May 2018 survey.
-- \ .
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Photo III-4. Seagrass in the eastern planted area during the October 2018 survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 111-3

Photo III-5. Natural seagrass in the reference area during the October 2018 survey.
,' ' 'II I(i 7" .;I' 1►
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Photo III-6. Seagrass in the western planted area during the May 2019 survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 111-4

Photo III-7. Natural seagrass in the reference area during the May 2019 survey.
iter
Photo III-8. Seagrass in the eastern planted area during the October 2019 survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN Ill-5

.
iftilllivvw
-7
Photo III-9. Natural seagrass in the reference area during the October 2019 survey.
4
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Photo III-10. Seagrass in the eastern planted area during the July-August 2020 survey.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN III-6

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CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN 111-7

•
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CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN IV-10

Appendix V
Representative Photos of Biota —July-August 2020
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN V-1

,
. 3 r .V '
♦ ' !^!.. Fri•t ; .i? 4i
. a, i l i a
ra t•`f . ,
1 ,� is
vr'• d _#J « 1 ,
•
•
1 4 or f -, s x_
i
Photo V-1. Close-up photo of barnacles and turf algae within the high elevation strata on the
wavebreak in July-August 2020.
i• t '.4.,r' • e d
'ems , s II i ��• -c* �
Ash ` `
,
� if4 Alin
` ;
P .I
*II .Ai/ ' ,..
,.
•
Photo V-2. Whelks and egg masses (most likely invasive Veined Rapa Whelk [Rapana venosa]) and
barnacles colonizing concrete within the medium elevation strata on a submerged portion
of the wavebreak in July-August 2020.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN V-2

Ito ..,
o
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Photo V-3. Hermit crab within the medium elevation strata on an exposed portion of the wavebreak
in July-August 2020. Note barnacles, oysters, and turf algae also in photo.
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Photo V-4. A feather blenny (Hypsoblennius hentz) (circled red) within the medium elevation strata
on a submerged portion of the wavebreak in July-August 2020. Note barnacles and oysters
also in photo.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN V-3

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Photo V-5. Oyster toadfish (Opsanus tau) (circled red)within the medium elevation strata on a
submerged portion of the wavebreak in July-August 2020.
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Photo V-6. A newly settled,juvenile Atlantic spadefish (Chaetodipterus faber) (circled red)just below
the water surface within the medium elevation strata on a submerged portion of the
wavebreak in July-August 2020.
CSA-NCDOT-FL-21-1830-2845-13-REP-01-FIN V-4

Brittingham, Cathy
From: Kathy Herring <[e-mail]>
Sent: Tuesday, January 21, 2020 7:56 AM
To: Brittingham, Cathy; Wilson, Travis W.;Ward, Garcy; [e-mail]; 'Barnes,
Kyle W CIV USARMY CESAW (US)'; Rivenbark, Chris; Daisey, Greg; fritz.rohde;Williams, Paul C;
Turchy, Michael A; Cox, Marissa R; Conforti, John G; McCann, Nora A;Weychert, Curtis R;
Deaton, Anne; Paugh, Leilani Y
Cc: Pete Stafford; Stanton, Tyler P; Fonseca, Mark ([e-mail]); Hodel, Erin
Subject: [External] FW: Bonner reports
Attachments: B2500_SAV_Year3_AnnualReport_FIN_17Dec2019.pdf; NCDOT_FL_19_1830_2845
BonnerBridge_Yr3_Biannual_Survey_Oct2019_2Dec_2019.pdf
CAUTION External email. Do not click links or open attachments unless you verify.Send all suspicious email as an attachment to
All,
We will present the annual Bonner SAV Mitigation update at the February 13th Interagency meeting. Please call me if you have
any questions.
Thanks,
Kathy
Note Our New Address!
From: Kathy Herring
Sent: Monday, December 30, 2019 9:42 AM
To: Brittingham, Cathy<[e-mail]>; Wilson,Travis W.<[e-mail]>; Ward, Garcy
<[e-mail]>; Staples,Shane<[e-mail]>; [e-mail]; 'Barnes, Kyle W
CIV USARMY CESAW (US)'<[e-mail]>; Rivenbark, Chris<[e-mail]>; Daisey, Greg
<[e-mail]>; [e-mail]; Williams, Paul C<[e-mail]>;Turchy, Michael A
<[e-mail]>; Cox, Marissa R<[e-mail]>; Conforti,John G <[e-mail]>; McCann, Nora A
<n a m cca n n@ n c d ot.gov>
Cc: Pete Stafford ([e-mail])<[e-mail]>;Stanton,Tyler P<[e-mail]>; Paugh, Leilani Y
<[e-mail]>; Fonseca, Mark([e-mail])<[e-mail]>; Hodel, Erin
<[e-mail]>
Subject: Bonner reports
All,
As per the CAMA Permit Major Modification, issued on 12/15/15, permit condition No. 21 that : "The permittee shall conduct an
annual meeting with DCM and other appropriate resource agencies to discuss and review the annual monitoring reports and
monitoring methodology for a minimum of five years after mitigation site construction." Attached are the reports from 2019 to
accompany the previous reports distributed to the group on 8/22/18. NCDOT will present an update and status report on the B-
2500 SAV mitigation at a time and place TBD in the upcoming months.
Please call me if you have any questions and please forward to anyone I may have missed.
Thank you and Happy New Year!
Kathy
KATHY HERRING
1

CSA
CSA Ocean Sciences Inc. www.csaocean.com
8502 SW Kansas Avenue Phone: [phone]
Stuart, Florida 34997 Fax: [phone]
02 December 2019
Mr.Tyler Stanton
North Carolina Department of Transportation
Project Development and Environmental Analysis Unit
1598 Mail Service Center
Raleigh, North Carolina 27699-1598
Subject: Summary of Year 3 Biannual Survey—October 2019—LETTER REPORT
Dear Mr. Stanton:
CSA Ocean Sciences Inc. (CSA)conducted the third and final Biannual Monitoring Survey(Year 3)for the
Bonner Bridge Seagrass Mitigation Site from 13 to 15 October 2019.Above-normal water levels at the
Site were recorded during the survey which prevented maintenance of the epibiota monitoring stations
on the middle and lower strata of the wavebreak structure (66%of the stations).Table 1 lists CSA's
previous activities and future scheduled surveys that encompass the long-term seagrass monitoring
program for this project. Beginning in Year 4(2020), only annual surveys will be conducted through 2021
to complete the program.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation Experiment Initiation _ May 2016 Complete
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 Nov.2016 to 18 Jan.2017 Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan.2017 Complete
Year 1 Biannual Monitoring Survey 2 to 4 Oct.2017 Complete
Year 2 Annual Monitoring Survey 13 to 17 May 2018 Complete
Year 2 Biannual Monitoring Survey 6 to 8 October 2018 Complete
Year 3 Annual Monitoring Survey 14 to 17 May 2019 Complete
Year 3 Biannual Monitoring Survey(this report) 13 to 15 October 2019 Complete
Year 4 Annual Monitoring Survey July 2020 Scheduled
Year 5 Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.
The Year 3 Biannual Monitoring Survey included:
• Monitoring of relocated seagrass in two planted areas and reference areas;

• Collection of sediment elevation data;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation;and
• Survey of epibiota on the wavebreak structure(high water levels during the October 2019 survey
prevented inventory and maintenance of all monitoring stations).
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I Seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina;September 2015) referenced in the
permit(Permit Modification No. 106-12)to ensure all monitoring requirements were met.
During the October 2019 survey,scientists observed patchy seagrass habitat consisting of two species of
seagrass (Halodule wrightii and Zostera marina). Halodule wrightii was the most prevalent species,
followed by Z. marina. Ruppia maritima, as distinguished by presence of flowering shoots, was not
observed during this survey.The major substrate type observed throughout the site was fine, siliceous
sand.Water levels were high during the survey, partially attributable to a full moon on 13 October 2019.
King tides also flanked the survey window and occurred in late September and late October in coastal
areas of North Carolina due to perigean spring tides (North Carolina King Tides Project, 20191).
Site conditions varied during the survey due to direction and strength of the wind.Average daily water
temperatures during the survey ranged from 20.2°C(68.4°F)to 22.68.4°C(73.0°F),with wind speeds
ranging from 4.3 to 34.4 kph (2.6 to 21.4 mph). Wind direction varied from southwest to south to
northeast.
MONITORING OF RELOCATED SEAGRASS
In May 2016, prior to construction of the wavebreak structure,seagrass patches within the structure
footprint and construction corridor were relocated to two planting areas on the south side of the
construction footprint.The percent cover of seagrass within each planting area and within the
surrounding reference area was evaluated immediately following relocation and during each monitoring
survey.
In October 2019,during the Year 3 Biannual Monitoring Survey,seagrasses were present within both
planted areas, but covert was relatively low at 14.0%and visibly dominated by H. wrightii(Table 23;
Photo 1).Average percent cover of total seagrass in reference areas was higher, at approximately 32.7%
(Table 2; Photo 2),where H. wrightii was also visibly dominant.A veneer of fine sediment and apparent
organic matter was present in varying thicknesses on all seagrass blades observed during the survey;
likely an aftereffect of Hurricane Dorian from suspension and subsequent settlement of these materials.
From the initial survey in May 2016(immediately following relocation)to the most recent survey in
October 2019,seagrass cover decreased by approximately 18.7% in the planted areas and decreased in
the reference area by approximately 16.4% (Table 2).The observed cover in the planted and reference
areas was lower than expected,given the survey occurred just after the end of seagrass growing season
1 http://nckingtides.web.unc.edu/; Last accessed 25 November 2019.
2 Cover is'specific cover'as quadrats are placed only within areas colonized by seagrass(as opposed to'areal cover'which
would include any unvegetated seafloor arising from random placement of quadrats).
3 The average BB scores were converted to percent cover for each area to allow interpolation of averaged BB scores that fall
between BB scale values(conversion was conducted by regressing the mid-point of percent cover associated within the range
covered by each BB scale value,on the associated BB scale value:Percent Cover=2.8108*[BB]2 232s)
CSA Ocean Sciences Inc. 2 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

(early fall), and may reflect impacts to seagrasses as a result of Hurricane Dorian which passed directly
over the Outer Banks as a Category 1 hurricane on 6 September 2019.
Photo 1. Representative image of a quadrat surveyed for percent cover of seagrass in the planted
areas. Photo taken in the eastern planted area on 15 October 2019.
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Photo 2. Representative image of a quadrat surveyed for percent cover of seagrass in the reference
area. Photo taken in the reference area on 15 October 2019.
CSA Ocean Sciences Inc. 3 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

Table 2. BB scores and associated percent cover*for seagrass within the planting and reference areas
for the Bonner Bridge Seagrass Mitigation Site.
Planting Area Reference Area
Survey Total Seagrass BB Percent Cover Total Seagrass BB Percent Cover
May 2016 3.0 32.70 3.60 49.10
January 2017 0.30 0.20 1.50 7.00
October 2017 0.00 0.00 4.00 62.10
May 2018 0.55 0.70 3.30 40.40
October 2018 2.11 14.90 5.00 100.00
May 2019 0.65 1.10 2.60 23.70
October 2019 2.05 14.00 3.00 32.70
Change from May 2016
to October 2019 -0.95 -18.7 -0.60 -16.4
(*)specific cover.
SEDIMENT ELEVATION
In May 2016, an approximately 3 to 4 m long(9.8 to 13.1 ft)stainless steel center rod was installed in
the middle of each of 40 randomly selected seagrass patches across the study area in addition to
four rods installed in sandy substrate,for a total of 44 sediment elevation monitoring stations. During
the initial survey in May 2016,the average rod height within patches was 6.85 cm (2.70 in.) above the
sediment and 6.88 cm (2.71 in.) above the sediment within sandy substrate (Table 3). In October 2019, a
total of 31 of the original 40 center rods in seagrass patches were located, with an average rod height of
14.50 cm (5.71 in.).Two of the four rods in sandy substrate were located with an average rod height of
12.50 cm (4.92 in.). Missing rods were likely buried at the time of the survey and were not located
despite attempts to uncover them. Sediment measurements for the buried rods were therefore unable
to be included, but their burial indicates increased sediment elevation at these locations.
Since the Post-Construction Baseline Survey in January 2017,sediment depth within the Bonner Bridge
Seagrass Mitigation study area has decreased (increased exposed rod height)within both the seagrass
patches and sandy substrate locations by 7.65 cm (3.01 in) and 5.62 cm (2.21 in), respectively(Table 4).
Table 3. Average rod height in centimeters above the seafloor for the sediment elevation monitoring
for the Bonner Bridge Seagrass Mitigation Site.
Survey Rods in Center of Seagrass Patches(cm) Rods in Sandy Substrate(cm)
May 2016 6.85 6.88
January 2017 11.03 12.40
October 2017 16.55 12.00
May 2018 14.73 14.00
October 2018 16.27 14.00
May 2019 15.81 10.50
October 2019 14.50 12.50
Change from May 2016
to October 2019 7.65 5.62
CSA Ocean Sciences Inc. 4 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

WAVE SENSORS
Wave sensors (RBRvirtuoso models)at the two long-term wave energy regime monitoring stations
(one each 25 m north and south of the structure)were retrieved, and data since the last monitoring
event(May 2019)were downloaded;all data were present. Basic univariate statistics on the waves are
given in Table 4. Note that the mean values for waves at these sites are small, because the majority of
waves occur during low wind conditions. In contrast, maximum values reveal the more episodic but
much larger wind wave heights. Ninety-nine percent of the wave heights observed on either side(north
or south of the structure)are less than approximately 0.25 m.
Table 4. Average, significant and maximum wave heights (m)for the north and south side permanent
wave sensors. N = number of 30 second burst measurements.
Side N Variable(m) Mean Maximum
Average wave height 0.04 0.44
North 67597 Significant' wave height 0.06 0.66
Maximum wave height 0.09 1.17
Average wave height 0.04 0.51
South 67417 Significant wave height 0.07 0.73
Maximum wave height 0.11 1.18
1 Significant wave height is the average height of the highest one-third of all waves measured.
Wave heights(mean maximum wave height, mean significant wave height and mean wave height)
associated with two recent major hurricanes, Florence(September 2018) and Dorian (September 2019)
were recorded by the wave sensors(Figures 1 and 2). For both storms,there were only moderate wave
heights, due primarily to a lack of water depth at the site,the result of storm-induced water level
effects.These storms have likely had an unknown but typically negative influence on seagrass cover at
the Site (sensu Fonseca et al. 20004).
Fonseca, M.S.,W.J. Kenworthy,and P.E.Whitfield.2000.Temporal dynamics of seagrass landscapes:a
preliminary comparison of chronic and extreme disturbance events. Biol. Mar. Medit.7:373-376.
CSA Ocean Sciences Inc. 5 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

HURRICANE FLORENCE-North Side I Triangles=Mean max wave ht(m)I Squares=Mean sig ware ht I Circles=Mean avg wave ht
xavghtm
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a)
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0.25
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II A
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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
I 1 I I 1 1 I r 1 1 1 I I 1 1 I I 1 I I I 1 I I 1 I
0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
I I I I I 1 I 1 I 1 I I I I I I I I I 1 I I I I I I
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 1 1 '1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
sasdate
HURRICANE FLORBKE-SwgIi Side(Triangles=Mean max wave ht(m)I Squares=Mean sip wave M I Circles=Mean arg wave ld
xavghtm
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0.35-
0.30-
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0.20
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0.10-
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9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
I I 1 1 r r I 1 r 1 1 1 1 1 1 1 1 1 I 1 1 I 1 1 1 1
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
I I I I I I 1 1 1 1 1 I I I 1 / 1 I I 1 I I I 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 B 8 8 8 8 8 8 8
sasdate
Figure 1. Wave heights recorded by wave sensors on the a) north and b)south sides of the wavebreak
from 01 to 26 September 2018,showing passage of Hurricane Florence in September 2018
at the Bonner Bridge Seagrass Mitigation Site.
CSA Ocean Sciences Inc. 6 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

HURRICANE DORIAN-North Side/Triangles=Mean max wave IA(m)I Squares=Mean sig ware M I Crcles=Mean arg ware II
xavghtm
0._40-
a)
0.35-
0.30
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0 0 00 00 0 0 8 8 8 8 88 8 9 9 99 99 9 9! ! ! ! 1 1 1 1 1 1 11 1 ! 1 1 2 2 2 2 23 3 0 0 11 11 1 1 15 6 7 8 9 0 1 7 8 9 01 23 4 5 1 1 1 1 1 1 11 1 1 11 11 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
sasdate
HURRICANE DORIAN-South Side/Triangles-Mean max wave MOO I Squares-Mean sig save IA I arches Mean imp wave ht
xavght m
0.40-
b)
0.35-
0.30
0.25-
0.20-
0.15
0.10
0.05
0.00-
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
8 8 8 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
/ I 1 ! 1 / / f ! I I ! ! 1 ! f ! 1 ! ! I l l l l l ! !
2 2 2 2 2 2 3 3 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2
4 5 6 7 8 9 0 1 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0
I I I I I I 1 I r I I I I I I I I I I I I I I I I I 1 !
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
sasdate
Figure 2. Wave heights recorded by wave sensors on the a) north and b)south sides of the wavebreak
from 24 August to 20 September 2019 showing passage of Hurricane Dorian in September
2019 at the Bonner Bridge Seagrass Mitigation Site.
CSA Ocean Sciences Inc. 7 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

One wave sensor was also utilized for WEMo model validation via systematic relocation across the Site
during the survey to collect data from 24 stations in total north and south of the structure. Preliminary
comparison of WEMo computations (predicted wave height)for these stations versus observed wave
heights and wind speeds collected in the field indicate a weak relationship between WEMo-predicted
values. This weak relationship is likely due to the inability to down-scale WEMo to observations at
spatial extents smaller than the resolution of the bathymetric data available to use in the WEMo
calculations.
EPIBIOTIC MONITORING STATIONS
Maintenance of the epibiotic monitoring stations (60 stations total) on the structure was not completed
fully during the Year 3 Biannual Survey due to above-average water levels which occurred during the
survey.The higher water levels prevented finding and cleaning of station identification tags and
re-etching of camera framer indentations on concrete for the middle and lower strata (66%of stations)
which were completely submerged throughout the 3-day survey. Since October 2018, barnacle and
oyster growth on the structure has prevented re-etching of the concrete on many stations in the middle
and lower strata. Photographs of each epibiotic monitoring station and subsequent quantitative percent
cover analyses are performed during all annual surveys and will be performed again during the next
survey in July 2020.
In general, less epibiotic cover was observed on the structure during the October 2019 survey and a
veneer of fine sediment and apparent organic matter was observed on all epibiota and the structure
itself(Photo 3). Cover of turf algae and barnacles appeared to have declined since the May 2019 survey.
The reduction in epibiota may have resulted from adverse effects of Hurricane Dorian (increased wave
energy and extremely low water levels following passage of the storm).
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Photo 3. Close-up photograph of oyster growth on middle strata of the wavebreak structure showing
a light coating of fine material on oysters, barnacles, and turf algae. Photo taken 15 October
2019. Image is approximately 0.25 m wide and 0.5 m high.
CSA Ocean Sciences Inc. 8 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

If you have any questions concerning this report, please feel free to contact me at(772) 219-3060 or
[e-mail].
Sincerely,
e7147.4..._4)
Erin Hodel
Senior Program Manager—Ports, Harbors, & Beaches
CSA Ocean Sciences Inc. 9 December 2019
CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02

-41•41A*
CSA
CSA Ooeen Sciences Incl.
SUMMARY OF YEAR 3 BIANNUAL SURVEY—OCTOBER 2019— LETTER REPORT
DOCUMENT NO. CSA-NCDOT-FL-19-1830-2845-19-MEM-01-VER02
VERSION DATE DESCRIPTION PREPARED BY: REVIEWED BY: APPROVED BY:
01 11/26/19 Initial draft for E. Hodel M. Fonseca E. Hodel
review
02 12/06/19 Revised draft E.Hodel C.Baumberger E.Hodel
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current revision.Controlled copies are available
on the Management System network site or on request from the Document Production team.

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B-2500 Bonner Bridge Seagrass Mitigation Site
Year 3 Annual Survey Report
December 2019
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Prepared for: Prepared by:
Environmental Analysis Unit CSA Ocean Sciences Inc.
North Carolina Department of Transportation 8502 SW Kansas Avenue
1598 Mail Service Center Stuart, Florida 34997
Raleigh, North Carolina 27699-1598

P‘b**
CSA
CSA Ocean Sciences Imo.
B-2500 Bonner Bridge Seagrass Mitigation Site
Baseline Monitoring Survey
DOCUMENT NO.CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN
Version Date Description Prepared by: Reviewed by: Approved by:
01 07/20/19 Initial draft for M.Fonseca E. Hodel E. Hodel
review
02 08/07/19 Revised draft M.Fonseca K. Metzger E. Hodel
FIN 12/17/19 Final M.Fonseca E. Hodel E. Hodel
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

Table of Contents
Page
List of Tables iv
List of Figures v
List of Photos vi
1.0 Introduction 1
2.0 Methods 2
Monitoring of Relocated Seagrass 4
Seagrass Cover 6
Sediment Elevation 7
Wave Regime and Model Validation 9
Epibiota Monitoring 15
3.0 Results 19
Monitoring of Relocated Seagrass 19
Seagrass Cover 25
Sediment Elevation 28
Wave Regime and Model Validation 37
Epibiota Monitoring 39
4.0 Conclusions 42
5.0 References 45
Appendices 47
Appendix I: Project Site Selection I-1
Appendix II: Bioturbation Experiment II-1
Appendix III: Representative Images of Biota—May 2019 III-1
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN iii

List of Tables
Table Page
1 Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation
Site 2
2 Braun-Blanquet scale(score) and percent cover scale values 6
3 Braun-Blanquet (BB)scores and associated percent cover for seagrass within the
planting and reference areas for the Bonner Bridge Seagrass Mitigation Site by
survey 20
4 One-way ANOVA testing differences in sediment elevation (ft, MLLW)from rods
installed at previous bioturbation patches between Survey 1 and subsequent
surveys 30
5 Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey.
Blue shading indicates a statistically significant (p<0.05)difference 31
6 Areas for the wave energy reduction zones depicted in Appendix I in both acres and
square meters 37
7 Percent cover of biota from concrete monitoring stations during the Baseline
Monitoring Survey in January 2017,the Year 2 Annual Monitoring Survey in May
2018 and the Year 3 Annual Monitoring Survey in May 2019 41
8 Percent cover of biota from rock monitoring stations during the Baseline Monitoring
Survey in January 2017,the Year 2 Annual Monitoring Survey in May 2018 and the
Year 3 Annual Monitoring Survey in May 2019 41
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN iv

t
,
List of Figures
Figure Page
1 Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site,
showing the position of the seagrass planting areas,the construction corridor, and
the structure itself 5
2 Schematic(not to scale) layout of the near-field (to wavebreak) sediment elevation
transects 10
3 Sand apron south of wall visually outlined 11
4 Stationary and temporary locations of the pressure sensors at the Bonner Bridge
Seagrass Mitigation Site 12
5 Epibiota monitoring stations on the wavebreak at the Bonner Bridge Seagrass
Mitigation Site 17
6 Baseline classification results identifying areas of seagrass (yellow)within the
Bonner Bridge Seagrass Mitigation Site for the 24 March 2017 overflight 26
7 Enlarged view of baseline aerial imagery(left)and classification results(right)
identifying areas of seagrass (yellow)within the Bonner Bridge Seagrass Mitigation
Site for the 18 April 2018 overflight 27
8 Change in sediment elevation (ft, MLLW)over time monitored at rods installed in
previous bioturbation study 29
9 Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital
elevation model at the Bonner Bridge Seagrass Mitigation Site prior to construction
of the wavebreak(ultimate location of wavebreak shown) 30
10 Panels 1-5; average sediment elevation (ft, MLLW) by side of wavebreak and
distance over time 32
11 Difference in hourly significant wave heights (m) between and north and south side
of the wavebreak structure for January 2017 through May 2019 38
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN v

List of Photos
Photo Page
1 Aerial image of Bonner Bridge. Source: http://www.kdhnc.com/667/Herbert-C-
Bonner-Bridge-Replacement-Project 1
2 Inverted "T"shape ruler used to measure rod height above or below the substrate
at the Bonner Bridge Seagrass Mitigation Site 8'
3 Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner
Bridge Seagrass Mitigation Site 8
4 Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site 13
5 Re-engineered wave sensor bracket installed in January 2018 to hold the sensor
vertical and further away from the sand surface 14
6 Example of numbered tag installed at every monitoring station on the wavebreak at
the Bonner Bridge Seagrass Mitigation Site 18
7 PVC camera mount framer used to photograph every monitoring station on the
wavebreak at the Bonner Bridge Seagrass Mitigation Site 18
8 Transplanted seagrass with clean blades appearing similar to surrounding natural
seagrass at the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey 21
9 Natural seagrass in the reference area showing blades covered with a layer of
epiphytes at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey 21
10 Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site
during the May 2018 survey 22
11 Representative image of in situ quadrat surveyed for percent cover in the planted
areas 22
12 Representative image of in situ quadrat surveyed for percent cover in the reference
area 23
13 Representative image of in situ quadrat surveyed for percent cover in the planted
areas 23
14 Representative image of in situ quadrat surveyed for percent cover in the reference
area 24
15 Representative photo of rock substrate for a high elevation monitoring station
(Station 27) showing wet rock on the structure at the Bonner Bridge Seagrass
Mitigation Site during the 2019 survey 39
16 Representative photo of concrete substrate for a middle elevation monitoring
station (Station 7) showing wet concrete, algae, and barnacle growth on the
structure at the Bonner Bridge Seagrass Mitigation Site during the May 2019 survey 40
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN vi

List of Photos
(Continued)
Photo Page
17 Representative photo of concrete substrate for a low elevation monitoring station
(Station 8)showing submerged concrete and barnacle growth on the structure at
the Bonner Bridge Seagrass Mitigation Site during the May 2019 survey 40
18 North-oriented view of the wavebreak installed in January 2017 at the Bonner
Bridge Seagrass Mitigation Site 43
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN vii

1.0 Introduction
The North Carolina Department of Transportation (NCDOT)contracted CSA Ocean Sciences Inc. (CSA) in
2012 (Contract No. 6300032017)to conduct in-kind seagrass (mixed Halodule wrightii, Ruppia maritima,
Zostera marina) mitigation of 1.28 acres (0.52 hectares)to compensate for losses anticipated to occur
during the replacement of the Herbert C. Bonner Bridge over Oregon Inlet, North Carolina (Photo 1).The
Bonner Bridge provides the only highway connection for Hatteras Island to the mainland in Dare County,
North Carolina and its replacement is currently under construction. Based on previous published
research in North Carolina (Fonseca et al., 1998, Fonseca et al., 2000, Kelly et al., 2001, Fonseca et al.,
2002) CSA conceptualized creating a wavebreak structure to modify existing, patchy seagrass habitat by
attenuating wave activity to promote more continuous, persistent seagrass coverage.This subsequent
increase in seagrass acreage was expected to meet NCDOT's seagrass mitigation requirements while
enhancing ecosystem services for the surrounding area.
r
ti
r
Photo 1. Aerial image of Bonner Bridge.
Source: http://www.kdhnc.com/667/Herbert-C-Bonner-Bridge-Replacement-Project.
CSA conducted the first Biannual Monitoring Survey(Year 1)for the Bonner Bridge Seagrass Mitigation
Site from 2 to 4 October 2017.The Year 1 Biannual Monitoring Survey was initially scheduled for
August 2017; however, due to tropical storm and hurricane activity and subsequent above-average
water depths in Pamlico Sound at the site,the survey was not conducted until early October 2017. In
2018,the spring survey(May—June)was conducted from 13 to 17 May. In 2019 the survey was
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 1

conducted from 14 to 17 May and provides the most recent data included in this Year 3 Annual Survey
Report.Table 1 has been updated and describes CSA's previous activities and future scheduled surveys.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation Experiment Initiation May 2016 Complete
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 Nov.2016 to 18 Jan.2017 Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan.2017 Complete
Year 1 Biannual Monitoring Survey 2 to 4 Oct.2017 Complete
Year 2 Annual Monitoring Survey 13 to 17 May 2018 Complete
Year 2 Biannual Monitoring Survey 6 to 8 October 2018 Complete
Year 3 Annual Monitoring Survey May 2019 Complete
Year 3 Biannual Monitoring Survey October 2019 Scheduled
Year 4 Annual Monitoring Survey July 2020 Scheduled
Year 5 Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.
2.0 Methods
The Year 1 Baseline and Biannual Survey Reports included:
• Observations of conditions
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Monitoring of selected bioturbation experiment stations and removal of mesh when found;
• Collection of sediment elevation data;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation; and f Qv�
• Maintenance of epibiota monitoring stations on the wavebreak structure." Q
The Year 2 Baseline and Biannual Survey Reports included: S1/4.121
C
• Observations of conditions
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data
o Seagrass patch elevation rods
o SEPI near-field wavebreak surveys
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation
• Reporting of wave sensor data throughout the site over this and the past surveys for WEMo
validation; and
• Monitoring of epibiota monitoring stations on the wavebreak structure
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 2

This Year 3 Annual Survey Report includes:
• Observations of conditions
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data
o Seagrass patch elevation rods
o SEPI near-field wavebreak surveys
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation
• Reporting of wave sensor data throughout the site over this and the past surveys for WEMo
validation; and
• Monitoring of epibiota monitoring stations on the wavebreak structure
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina; September 2015) referenced in the
permit (Permit Modification No. 106-12)to ensure all monitoring requirements were met.
During the October 2017 survey,scientists observed patchy seagrass habitat consisting of three species
of seagrass (Z. marina, H. wrightii, and R. maritima). Halodule wrightii was the most prevalent species,
followed by Z. marina and then R. maritima.The major substrate type observed throughout the site was
fine sand. Limited vessel traffic was observed during on-site surveys within the immediate vicinity. Site
conditions were relatively consistent during the survey, with slight variations due to direction and
strength of the wind.Average daily water temperatures during the survey ranged from 22°C(72°F)to
23°C(73°F),with wind speeds ranging from 26.5 to 31.3 kph (16.4 to 19.5 mph).Wind direction was
predominately out of the north.
In May 2018,scientists again observed patchy seagrass habitat consisting of three species of seagrass
(Z. marina, H. wrightii, and R. maritima). Halodule wrightii and Z. marina were both commonly observed
0�0 while R. maritima was rarely observed.The major substrate type observed throughout the site was fine
siliceous sand. Limited vessel traffic was observed during on-site surveys within the immediate vicinity.
\ Site conditions were relatively consistent during the survey,with slight variations due to direction and
strength of the wind. Average daily water temperatures during the survey ranged from 23.4°C(74.2°F)
(rA to 24.8°C(76.7°F),with wind speeds ranging from 7.6 to 41.1 kph (4.7 to 25.5 mph). Wind direction was
1mar\ \ predominately south-southwest.
1 ` During the October 2018 survey,scientists observed patchy seagrass habitat consisting of two species of
seagrass (H. wrightii and Z. marina). Halodule wrightii was the most prevalent species,followed by Z.
marina. Ruppia maritima, as distinguished by presence of flowering shoots,was not observed during
this survey. The major substrate type observed throughout the site was fine sand. Limited vessel traffic
was observed within the immediate vicinity of the wavebreak structure. Site conditions were relatively
consistent during the survey, with slight variations due to direction and strength of the wind.Average
daily water temperatures during the survey ranged from 25.7°C(78.3°F)to 27.4°C(81.3°F),with wind
speeds ranging from 7.6 to 27.7 kph (4.7 to 17.2 mph). Wind direction was predominately out of the
east-northeast.
During the May 2019 survey,scientists observed patchy seagrass habitat consisting of three species of
seagrass (H. wrightii, R. maritima,and Z. marina). Halodule wrightii was the most prevalent species,
closely followed by Z. marina. Ruppia maritima was rarely observed but present.The major substrate
type observed throughout the site was fine sand. Limited vessel traffic was observed within the
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN 3

immediate vicinity of the wavebreak structure. Site conditions were relatively consistent during the
survey, with slight variations due to direction and strength of the wind. Average daily water
temperatures during the survey ranged from 17.0°C(62.6°F)to 19.6°C(67.3°F),with wind speeds
ranging from 1.6 to 45.1 kph (1 to 28 mph). Wind direction was predominantly out of the west.
Sections of this report that refer to construction and engineering activities or permits where originally
developed using English units,will follow the convention of reporting first in English units and then
parenthetically in metric units. For the sections of the report not directly associated with structural
engineering,the convention of reporting will be metric units followed by English units parenthetically.
Sections of the early reports describing initial project activities have now been moved to Appendices in
order to focus on long-term post-construction monitoring. Project Site Selection and Project Engineering
and Design sections were initially described here in previous reports.This historical material has now
been moved to Appendix I. Additionally,the description of an attempted experiment to assess the
relative contribution of bioturbation to patch maintenance (versus wave energy) has been moved to
Appendix II.
MONITORING OF RELOCATED SEAGRASS
In 2016, prior to installation of the wavebreak structure,the State of North Carolina Department of
Environmental Quality and Coastal Resources Commission permit(Permit Modification No. 106-12)
required any seagrass within the structure footprint and the construction corridor to be moved to the
lee side of the structure onsite. In May 2016, seagrass patches within the structure footprint and
construction corridor were relocated to two planting areas on the south side of the construction
footprint (Figure 1).
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 4

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Figure 1. Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site,showing the position of the seagrass planting
areas,the construction corridor, and the structure itself. Examples of randomly selected seagrass survey points are shown for
surveys within the planted areas and nearby reference locations.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 5

Percent cover of seagrass within relocation areas was evaluated immediately after transplanting. Each
time, scientists navigated to 10 pre-selected locations (proportionally assigned to seven locations in the
larger eastern relocation area and three in the smaller western relocation area)within the planting
areas using the Trimble Geo XH GeoExplorer 2008 Series GPS.
To compare the colonization of the planted areas to the surrounding natural areas,five additional
random locations were selected in the surrounding natural areas (reference area)within a 50-meter
(164-foot) distance of the planting areas (Figure 1). At each location, a 1-m2 (11-ft2) quadrat was
centered over each point and percent cover of seagrass was assessed using a modified Braun-Blanquet
(BB) cover and abundance technique (Braun-Blanquet, 1972; Kenworthy and Schwarzchild, 1997;
Fourqurean et al., 2001).Within the quadrat a BB scale value (Table 2)was independently evaluated for
percent cover of each seagrass species as well as total seagrass. Average BB scores were then converted
to percent cover for each area to allow interpolation of averaged BB scores that fall between BB scale
values (conversion is conducted by regressing the mid-point of percent cover associated within the
range covered by each BB scale value, on the associated BB scale value:
Percent Cover= 2.8108*[BB]2.2325)
Table 2. Braun-Blanquet scale(score) and percent cover scale values (Braun-Blanquet, 1972).
Braun-Blanquet Scale(Score) Percent Cover(%)
0.0 Not present
0.1 Solitary specimen
0.5 Few with small cover
1 Numerous, but<5
2 5 to 25
3 25 to 50
4 50 to 75
5 75 to 100
SEAGRASS COVER
Seagrass cover was determined by classifying areas of seagrass occurring within the Bonner Bridge
Seagrass Mitigation Site based on aerial imagery. A georeferenced, high-resolution mosaicked aerial
image(collected by NCDOT on 18 April 2018)was used for the first classification of seagrass areas.The
aerial image was color-infrared (CIR)with a resolution of 0.08 m (0.25 ft).The image was subdivided into
separate classification areas of interest (AOI) based on similar pixel spectral signature ranges. Separate
classification of each AOI helped to eliminate variations in reflectance and environmental conditions
across the entire project area in order to reduce classification confusion. An unsupervised classification
was then performed on each classification AOI using a combination of iso cluster and maximum
likelihood techniques using ESRI ArcGIS 10.4 software.After running the unsupervised classifications,
each AOI was manually interpreted by denoting visually apparent classes of seagrass and classes of
non-seagrass. Spectral noise and holes within the classification results were removed and corrected
using a combination of majority filter, region group, set null (enhanced boundary edges and removed
groups of small non-contiguous pixels that were smaller than a specified value), and eliminate polygon
part (eliminated areas that were less than a specified value)tools in ArcGIS. Lastly, a manual
classification technique was then applied to the classification with guidance from a GIS analyst.
This consisted of removing areas of over-classification and adding-in (digitizing) areas where
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 6

under-classification occurred, again based on visually apparent seagrass cover. Following the
18 April 2018 overflight, no further overflight data are being processed under this award.
SEDIMENT ELEVATION
Sediment elevation is being documented with three methods:
1. Rod Heights- measurements of sediment height relative to 2 m long rods installed to near the
sediment surface in seagrass patches used for the previous bioturbation studies,
2. USV Digital Elevation Model-a broad-scale digital elevation model created using an RTK-equipped
(real-time kinematic) unmanned surface vehicle (USV), and
3. Near-field Transect Sediment Elevation Survey- Near-field sediment elevation measurements along
transects north and south of the wavebreak.
Rod Heights:This method utilized during all monitoring surveys was by direct measurement of the
height of the center rod above the sediment at each of the 40 stations originally established for the
bioturbation experiment (see Appendix II). At each station,the rod height above the sediment was
measured using a meter stick fastened to a piece of wood (24 cm x 5 cm x 5 cm [18 in x 2 in x 2 in]).The
0-mark on the meter stick was attached to the center of the wood piece creating an inverted "T" shape
(Photo 2).The wood was laid flush against the seafloor to provide more surface area to avoid the ruler
sinking into the substrate.The meter stick was placed next to the rod to obtain the measurement of the
rod height above the substrate. In addition to the 40 center rods,four additional sediment rods(one per
wave energy regime)were installed in sandy substrate and rod height above the substrate was
measured for each.
This monitoring is continuing, and updated results are provided in this report. Change in sediment
elevation among surveys and across the wave energy strata was computed for each combination of
survey times(survey 1 vs 2, 1 vs 3, 1 vs 4, 2 vs 3, 2 vs 4 and 3 vs 4).The differences in change in sediment
elevation among strata for each comparison of survey times were compared in a 1-way ANOVA using
PROC GLM in SAS 9.2 after In+ 10 transformation (to avoid negative numbers and address any
non-normality of the data).
USV Digital Elevation Model:A second method was employed to evaluate the entire area forecast to be
affected by the wavebreak. In June 2016, CSA used a USV to develop a sediment digital elevation model
to document changes in shoal elevation associated with the wavebreak installation.The USV(Photo 3)
was pre-programmed to run a pre-selected geographic grid at 50-m (164-ft)spacing which encompassed
the entire site. Bathymetry data was collected using duel frequency, single beam sonar at a rate of
220 to 224 kHz. A Trimble RTK system (RTK)was mounted on the USV to integrate real time navigation
while the USV ran the pre-programmed grid lines (speed of approximately 9 kph [5.7 mph]).The RTK had
a horizontal and vertical accuracy of 2 cm (±0.787 in)and real-time tidal corrections were applied to
accurately determine water levels across the site.This survey will be repeated at the end of the five-year
monitoring period in 2021.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 7

41110.411
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Photo 2. Inverted "T" shape ruler used to measure rod height above or below the substrate at the
Bonner Bridge Seagrass Mitigation Site.
•
Photo 3. Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner Bridge
Seagrass Mitigation Site.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 8

Near-field Transect Sediment Elevation Survey: In June 2017, a third method of sediment elevation
assessment was initiated. SEPI Engineering Inc. (SEPI)was contracted by NCDOT to conduct high density,
near-field sediment elevation measures in the vicinity of the wavebreak structure. North-south oriented
transects were established at five equally spaced locations centered on the wavebreak(Figure 2)and
sediment elevations corrected to MLLW surveyed (June 2017,September 2017 and then monthly
starting January 2018; reported here through June of 2018).Transects were placed on both the north
and south side of the wavebreak. In 2017,elevations at distances of 0(at the edge of the wavebreak
structure),5, 10,20, 50,75, and 100 ft were recorded. In January of 2018 that changed to increments of
5 feet out to 50 ft and then at 75 and 100 ft to improve sensitivity of detecting any systematic change in
sediment elevation. Starting in June of 2018, distances of 125 and 150 ft were added to ensure elevation
samples were taken beyond the apparent apron of recently moved sand seen in aerial images (Figure 3).
These data have been provided to CSA and were analyzed for this report. Elevations were compared in a
2-way ANOVA using PROC GLM in SAS 9.2 after In + 10 transformation (to avoid negative numbers and
address any non-normality of the data). Main effects were distance from the wall and side of the wall,
tested at individual dates along with assessment for interaction of main effects.
WAVE REGIME AND MODEL VALIDATION
Long Term Wave Regime: Long-term wave energy regime monitoring stations were placed at the
Bonner Bridge Seagrass Mitigation Site in "Month Year" using pressure sensor loggers to record wave
characteristics. Starting in January 2017 two pressure sensors (RBRvirtuoso models)were deployed at
stationary locations 25 m (82 ft) in front (north) of and behind (south)the wavebreak structure
(Figure 4). Pressure sensors were cylindrical and approximately 5 cm (2 in) in diameter by 25 cm (10 in)
long and were mounted in a locked casing horizontally on the seafloor approximately 15 cm (6 in) above
the substrate on a solid base, concrete-filled pillar set 0.91 m (3 ft) into the seafloor(Photo 4). Pressure
sensors were set to record bursts of pressure data every 30 minutes at a sampling rate of 4 Hz for
128 seconds.These data also provide water level and tide documentation specifically for the site in
order to evaluate the wave energy regime impinging on the north and south faces of the wavebreak
structure.
In November 2017,the sensors were removed and sent back to the manufacturer(RBR)for calibration
and assessment of impacts from sand impaction and biofouling that had occurred around the wave
sensor port.This servicing caused the sensors to be out of service until their re-deployment on
16 January 2018. Communication with the RBR technical representatives indicated that the sediment
impaction and biofouling did not affect the detection of wave characteristics. Nonetheless, upon
redeployment,the sensor brackets were revised to hold the sensors in a vertical posture and with the
wave sensor window down-facing(Photo 5) in order to minimize sand collection in the sensor port
through gravity.The sensors were re-deployed in January 2018 and have been recording continuously
since that time.The entire January 2017—May 2019 data are reported here.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 9

Bonner wavebreak sediment elevation transect layout
15 sediment elevations per tra n sect at 0,5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 125, 150 feet
15 sediment elevation locations pertransect
Notto scale
Wavebreak
Pile `— __
Pile 76
Pile 25
Pile 101
44
Pile 1
All transects at a right angle to this red dashed baseline
Figure 2. Schematic (not to scale) layout of the near-field (to wavebreak) sediment elevation transects.
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN 10

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CSA-NCDO T-FL-19-1830-2845-11-REP-01-FIN 11

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0 50 100 200 Meters
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Figure 4. Stationary and temporary locations of the pressure sensors at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 12

OKING
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Photo 4. Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site.The hinged bracket is shown being
lifted; a disposable padlock is installed through the hinged piece to keep the sensor secure.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 13

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Photo 5. Re-engineered wave sensor bracket installed in January 2018 to hold the sensor vertical and
further away from the sand surface.
WEMo model validation:This is being developed through opportunistic sampling. During times of onsite
monitoring surveys, an RBR sensor was systematically but temporarily relocated across the site in a grid
pattern (Figure 4)to obtain a spatial assessment of predicted (WEMo computation to follow based on
water depth and wind conditions of the survey date)versus observed wave heights from the mobile
sensor.This spatial assessment was performed on 18 May 2016; 15 January 2017;4 October 2017;
15 May 2018; 7 October 2018; and 16 May 2019 to provide a geographically articulated assessment of
wave energy distribution with regard to prevailing conditions.The relocated pressure sensor was set to
record bursts of pressure data at a sampling rate of 4 Hz for 128 seconds during this sampling. During
these surveys one of the long-term RBR sensors was used. During each survey, a scientist recorded the
wind speed using hand-held anemometers as well as wind direction prior to sampling and again after
sampling was complete.Wave data from pressure sensors were downloaded into Ruskin software
(V1.13.7) and exported to Microsoft Excel for analysis.Analysis will be comprised of simple univariate
statistics of wind speed and predicted versus observed regression to determine the ability of the
WEMo-derived forecast to downscale to the 50 m scale.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 14

EPIBIOTA MONITORING
Epibiota monitoring on the wavebreak was initiated in January 2017 through the establishment of
randomly-placed, permanent monitoring stations (Figure 5). Digital photographs were recorded at each
station as a time-zero (uncolonized) baseline against which subsequent epibiota colonization will be
compared for each survey time. Stations were stratified by the sides of the wavebreak(30 on the
exposed side [north] and 30 on the sheltered [south] side) at different vertical elevations related to the
individual wave attenuator unit placement (high, middle,and low).Ten replicate stations were randomly
assigned per elevation on either side of the wavebreak for a total of 60 monitoring stations. Random
locations were selected along the wavebreak and a vertical elevation was randomly assigned to each
location. Scientists used the Trimble GPS to navigate to the pre-selected random monitoring
station/elevation replicate along the wavebreak. Monitoring stations were separated by a minimum of
one Reefmaker unit.The exact horizontal location of the monitoring station on a wave attenuator unit
was visually determined where rock placement was closest to the edge of the concrete, making them
easier to photograph.Some wave attenuator units had smaller rock embedded in the concrete,so often
two small rocks were selected for monitoring.To identify the precise monitoring location and allow
precise alignment for subsequent photographs, a numbered tag was installed on the rock immediately
to the right of the selected rock(s)to be monitored (Photo 6) and alignment points marked on the
concrete surface.
A Sony A5000 digital camera in an underwater housing was installed on a PVC camera mount framer to
photograph the concrete and rock(s) at each monitoring station.The PVC frame (Photo 7)was included
in every photo to ensure standardization of photo size(dimension of the frame was 20.3 cm x 30.5 cm
[8 in x 12 in]).The camera housing was fixed to the framer with a distance of 25.7 cm (10 in)from the
housing lens to the outer edge of the frame.
To photograph the concrete portion of the wave attenuator units,the entire framer was placed flush
with the side of the concrete,so the bottom edge of the concrete was included within the frame.To
photograph the rock(s),the bottom of the framer was placed flush with the top edge of the concrete
layer(where the selected rock was embedded) and the top of the framer rested on the concrete layer
located above the selected rock(s) (approximately 152 angle).
During the May 2018 survey,the low elevation strata monitoring stations were entirely submerged
during all observed tidal stages.This coupled with high turbidity levels, reduced visibility to less than one
foot.As a result,the method used to photograph the low elevation stations was slightly modified.The
camera was removed from the framer to allow capture of close-up photos within visibility limits.The
framer was still held against the concrete as described previously,yet due to the decreased distance
between the camera and the rock or concrete, multiple photographs were collected to image the entire
area within the framer(typically four photos).The multiple photographs were then stitched together
using Adobe® Photoshop®to create a single photograph of each low strata rock or concrete monitoring
station.This methodology was not necessary in subsequent surveys (October 2018 and May 2019)as
visibility was sufficient for photographing the original area contained within the framer, resulting in one
image.
One photo of the concrete and one photo of the rock(s)were collected for all 60 monitoring stations,
resulting in 120 digital images. Digital images were processed and analyzed using Coral Point Count with
Microsoft Excel extensions (CPCe)V4.1 software analysis program (Kohler and Gill, 2006). CPCe utilizes
the random point count method described by Bohnsack(1979)to accurately estimate percent cover of
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 15

benthic organisms and substrate from digital images. Because the rocks were all different sizes, it was
necessary to assign a number of random points that was proportional to the size of the rock
(i.e., a larger rock would have a greater number of random points assigned).The total area of evaluated
rock was calculated for each image using the measurement tool in CPCe. For purposes of this
assessment,we assumed that all rocks were equidistant from the camera lens. From these calculations,
average rock size was determined to be 112.4 cm'and was assigned 10 random points.The number of
random points assigned to each image was then increased or decreased proportionally to the size of the
rock(s);the number of random points for rock images ranged from four to 22. Because the area of
concrete assessed was the same in each photo, all concrete images were assigned the same number of
random points (41), and points were restricted to the area of the photograph containing concrete.
Random points were projected on each image, and the biota or substrate located beneath each point
was identified to the lowest possible taxonomic level (for the time-zero images, no biota were
detected). Data from each image were assembled in a spreadsheet for percent cover calculations and
subsequent comparative analysis.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 16

75•35'14'W 75'35'13'W 75•3512'W 75'35'11'W 75°35'10'W 75'35'9 W 75°35'8'W Z
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0 25 50 100 Meters
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CSA Coordinate System WGS 1984 UTM Zone 18N
Figure 5. Epibiota monitoring stations on the wavebreak at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 17

•
4,1
•
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Photo 6. Example of numbered tag installed at every monitoring station on the wavebreak at the
Bonner Bridge Seagrass Mitigation Site.
•
♦ 0,4
t r
•
Photo 7. PVC camera mount framer used to photograph every monitoring station on the wavebreak at
the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 18

3.0 Results
During visits to the site,scientists have consistently observed that the Bonner Bridge Seagrass Mitigation
Site was composed of patchy seagrass habitat consisting of multiple species including Z. marina,
H. wrightii, and R. maritima.Very fine sand (visual observation)sediments has consistently been the
dominant substrate type observed. Limited vessel traffic has been observed during onsite surveys within
the immediate vicinity although small commercial crabbing vessels have been observed crossing the
general shoal area.
Site conditions varied during each survey and were largely driven by direction and strength of the wind.
Strong northeasterly winds on site resulted in lowered water level at the site and strong southwesterly
winds resulted in higher water levels. Current speeds have been consistently low, ranging only between
9.8 and 12.9 cm s-1,with a mean of 11.2 cm s-1. During the May 2019 survey average current speed was
10.3 cm s-1.
During the May 2019 survey, scientists again observed patchy seagrass habitat consisting primarily of
two species of seagrass(H. wrightii and Z. marina). Halodule wrightii was the most prevalent species,
followed by Z. marina. Ruppia maritima, was only rarely during this survey.The major substrate type
observed throughout the site was fine sand. Limited vessel traffic was observed within the immediate
vicinity of the wavebreak structure. Site conditions were relatively consistent during the survey,with
slight variations due to direction and strength of the wind.
Average daily water temperatures during monitoring surveys (May and October) have ranged from 17°C
(62.6°F)to 24.8°C (76.6°F). During the May 2019 survey water temperature ranged from 17.0°C(62.6°F)
to 19.6°C(67.3°F). Average wind speeds during surveys have ranged from 12 to 30 kph (7.5 to 18.5 mph)
with maximum wind speeds ranging from 15 to 34 kph (8 to 21.3 mph)from either northeast or west
and south-southwest directions. During the May 2019 survey wind speeds ranged from 10.3 to 13 kph
(6.4 to 8.1 mph) predominantly from the west.
MONITORING OF RELOCATED SEAGRASS
Prior to construction, seagrass patches within the structure footprint and construction corridor were
relocated to two planting areas on the lee side of the wavebreak structure (Figure 1). In May 2016,
immediately after relocation,the percent covers of seagrass was evaluated within the relocation areas
and within the surrounding reference area. Upon completion of relocation, percent cover of seagrass
was 32.7%for the relocation areas and 49.1)for the reference area (BB scores of 3.0 and 3.6,
respectively2).Transplanted seagrass within the relocation areas appeared similar to the surrounding
natural seagrass and the borders of the planting areas were visibly indistinguishable (Photo 8).All
seagrass blades were bright green and visibly clear of epiphytic growth.
In January 2017, immediately following construction of the wavebreak structure, the percent cover of
seagrass within the planting areas was evaluated again.The planting areas had a percent cover of
0.2%and the natural reference areas had a percent cover of 7%(BB scores of 0.2 and 1.5, respectively)
1 Cover is'specific cover'as quadrats are placed only within areas colonized by seagrass(as opposed to'areal cover'which
would include any unvegetated seafloor arising from random placement of quadrats)
2 The average BB scores were converted to percent cover for each area to allow interpolation of averaged BB scores that fall
between BB scale values(conversion was conducted by regressing the mid-point of percent cover associated within the range
covered by each BB scale value,on the associated BB scale value:Percent Cover=2.8108*[BB]2.2325)
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 19

(Table 3). In January 2017,a brown epiphytic layer covered the majority of the visible seagrass blades
and small tufts of brown macroalgae were observed colonizing the substrate often mixed in with
seagrass (Photo 9). Seagrass cover declined by 32.5% in the planting areas and 42.1% in the reference
areas, indicating a substantial overall drop in coverage.
In October 2017, no seagrass was observed in the planted areas. Cover in the reference areas was
approximately 62%(Table 3),well above the baseline cover of 49%observed in May 2016. Seasonality in
seagrass growth may be responsible for the higher cover observed in October,with higher cover
expected at the end of growing season in October versus the beginning of growing season in May.
In May 2018,sparse seagrass was observed in the planted areas, but cover was still<1%, marking a
decrease of approximately 32%since the initial survey in May 2016(Table 3). Cover in the reference
area was approximately 40%(Photo 10),similar to the cover observed in May 2016.
In October 2018,at the time of the Year 2 Biannual Monitoring Survey, seagrasses were present within
both planted areas, but cover was relatively low at 14.9%, and dominated by H. wrightii(Table 3;
Photo 11).Average percent cover of total seagrass in reference areas was high at approximately 100%
(Table 3; Photo 12),where H. wrightii was also dominant.
In May 2019 (this report)seagrasses were again present within both planting areas but no discernable
cover was found in the easternmost planting block and percent cover in the western block was 15.8%
(Table 3, Photo 13).The reference cover was down to 23.7% (from 100% in the previous survey;Table 3,
Photo 14).
Table 3. Braun-Blanquet (BB)scores and associated percent cover for seagrass within the planting
and reference areas for the Bonner Bridge Seagrass Mitigation Site by survey.
Planting Area Reference Area
Survey Average Seagrass Average Percent Average Seagrass Average Percent
BB Cover BB Cover
May 2016 3.0 32.7 3.6 49.1
January 2017 0.3 0.2 1.5 7.0
October 2017 0.0 0.0 4.0 62.1
May 2018 0.55 0.7 3.3 40.4
October 2018 2.11 14.9 5.0 100
May 2019 0.65 1.1 2.6 23.7
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 20

4
le
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Photo 8. Transplanted seagrass with clean blades appearing similar to surrounding natural seagrass at
the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey.
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Photo 9. Natural seagrass in the reference area showing blades covered with a layer of epiphytes at
the Bonner Bridge Seagrass Mitigation Site during the January 2017 survey.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 21

•
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4
•
Photo 10. Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site during
the May 2018 survey.
\ _af,n/ ,i‘‘. ,
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Photo 11. Representative image of in situ quadrat surveyed for percent cover in the planted areas.
Photo taken in the eastern planted area on 7 October 2018.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 22

Photo 12. Representative image of in situ quadrat surveyed for percent cover in the reference area.
Photo taken in the reference area on 7 October 2018.
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Photo taken in the western area on 14 May 2019.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 23

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r'�
Photo 14. Representative image of in situ quadrat surveyed for percent cover in the reference area.
Photo taken in the reference area on 14 May 2019.
Several factors may have contributed to the loss of seagrass within the planted areas that was initially
observed in January 2017. Seagrass was relocated to gaps within natural seagrass patches in May 2016
prior to installation of the wavebreak structure. Construction was originally scheduled for June 2016 but
delayed until November 2016 and completed in January 2017. Previous studies have shown if seagrass is
relocated to areas naturally devoid of seagrass without modifying the existing environment, natural
processes will continue to preside and the relocated seagrass should not necessarily persist
(Fonseca et al., 1998).Additionally, Hurricane Matthew passed through the Pamlico Sound and
surrounding areas on 8 and 9 October 2016,five months after seagrass relocation, prior to the
installation of the wavebreak structure. The hurricane had average wind speeds ranging from 32 to
64 kph (20 to 40 mph)with maximum wind speeds of 129 kph (80 mph) initially from the north,and
then switching direction out of the southeast as the storm passed. Severe flooding occurred along the
coast with an average rainfall of 22.1 cm (8.7 in) (http://www.weather.gov/mhx/MatthewSummary). It
is possible that the relocated seagrass had not fully established a sufficiently robust root and rhizome
system during the five months from relocation to the storm event, leaving them susceptible to erosion.
Additionally,sand accumulation on the south side of the structure due to scouring has been observed in
physical monitoring surveys and may be inhibiting seagrass survival in the immediately adjacent planted
areas.
•j, Seagrass cover in coastal North Carolina naturally declines in winter months (Thayer et al. 1984) and
l�`� therefore lower cover was expected during the January 2017 survey. Cover in the reference area was
S
also very low at this time(7%),which also may have been attributable to Hurricane Matthew and/or the
/Cl/TY sampling event occurring in winter.Since the January 2017 survey,seagrass in the planted areas has not
J _l,)i recovered and cover remains<1%. However,seagrass in the reference area has recovered and percent
� cover is similar to that observed during the initial survey in May 2016.`(�
Sam
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 24

With this survey, seagrass monitoring has now been performed for three years post-relocation.At this
point,the dramatic fluctuation of cover among surveys in both the planted blocks and reference areas is
likely the result of storm impacts and a highly patchy and shifting seagrass distribution. Percent cover
has thus far averaged 8.3% in the planted areas andt 46.8% in the reference areas.
SEAGRASS COVER 1,�(\C�v Gar\ \n cj1 c \ Igh'J✓1
The Bonner Bridge Seagrass Mitigation Site was forecast to include 301.6 acres (122.1 hectares), and
boundaries were determined by using the wave forecast model prediction. Seagrass cover within these
boundaries was determined by classifying areas of seagrass based on aerial imagery provided by NCDOT.
In 2018, classification resulted in 24.9 acres (10.1 hectares (versus 33.4 acres [13.5 hectares] in 2017)of
seagrass cover over the 301.6-acre (122.1-hectare)site(Figures 6 [2017] and 7 [2018]). By visual
estimation it appears that seagrass cover was lost in the patchy areas north and east of the wavebreak.
In aquatic systems,classification methods rarely achieve 100%accuracy.This is because, unlike
terrestrial systems,whose classification is limited primarily by atmospheric conditions, classification of
aquatic systems,especially benthic components, is limited by both atmospheric and water conditions.
Thus,the accuracy of seagrass classification largely depends on water clarity and sea surface condition
at the time of imagery acquisition. Weather events affect waves on the water surface which actively
degrade visualization of the seafloor, as well as water clarity. In addition,wind events occurring
immediately prior to imagery collection may cause latent sediment suspension that negatively impact
results. Finally, many seagrass patches were interdigitated with sand and often non-contiguous,which
complicates precise delineation. In addition to atmospheric and water column effects, mosaicking of the
image produced shading gradients which interfered with seagrass classification accuracy of the seagrass
areas and appeared to be the source of most inaccuracy.An absence of ground control points taken in
association with the imagery impeded further accuracy assessment. In both 2017 and 2018,
interpretation of seagrass cover was compromised by the generally poor quality of the imagery. Large
areas of high surface reflectance and presence of white'flecks' in the imagery over much of the AOI
impaired or completely prevented interpretation of seagrass cover. Discrimination of seagrass cover
apart from sand was also made difficult because of low contrast among the two habitat types.This may
have resulted from high water levels, high visibility, low sun intensity or some combination thereof.
Upcoming utilization of low-altitude, high resolution imagery should improve seagrass cover delineation.
Following the 18 April 2018 overflight, no further overflight data are being processed under this award.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 25

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0 50 100 200 Meters
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CSA Coordinate System NAD 1983 StatePlane North Carolina FIPS 3200 Feet
Figure 6. Baseline classification results identifying areas of seagrass (yellow)within the Bonner
Bridge Seagrass Mitigation Site for the 24 March 2017 overflight.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 26

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0 100 200 400 Meters
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CBA Coordinate System NAD 1983 StatePlane North Carolina FIPS 3200 Feet
Figure 7. Enlarged view of baseline aerial imagery(left) and classification results (right) identifying
areas of seagrass (yellow)within the Bonner Bridge Seagrass Mitigation Site for the 18 April
2018 overflight.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 27

SEDIMENT ELEVATION
Rod Heights: Sediment elevation was monitored across the entire site by measuring the center rods at
40 seagrass patches selected for a bioturbation study(see Appendix II for description of this
since-terminated experiment) and four additional sediment rods placed in sandy substrate.These
40 rods were installed in May 2016 at locations randomly selected from within strata (10 per strata)
defined by the forecasted wave reduction pattern following wavebreak placement (high wave energy
reduction =>66%; moderate reduction =34 to 66%, low reduction =5 to 33%,and ambient or reference
=<5% reduction (Appendix Figure II-1). Across all surveys, no rods were located that were below the
sediment surface despite extensive searching and probing. If buried rods were not located,this would
suggest that the surveys were potentially biased towards measurements indicating a lower elevation of
the sediment surface.
The average rod height above the sediment in May 2016 was 6.8 cm (2.7 in).The average height of the
four sediment rods above the sediment was 6.9 cm (2.7 in). In January 2017, a total of 32 center rods
were relocated and the average rod height was 11.0 cm (4.3 in).Two of the four sediment rods were
relocated, and the average rod height was 12.4 cm (4.9 in).The eight center rods not located may be
deeply buried and future attempts will be made to locate them. If they were deeply buried,then the
average rod height would decrease.
In October 2017,sediment elevation was monitored at the center rod of the 14 patches monitored for
bioturbation in addition to the original 4 rods in sandy substrate.The center rod was not located (likely
due to burial) at 3 of the 14 seagrass patch locations and 1 sandy substrate location.The average height
of center rods in seagrass patches was 16.5 cm (6.5 in.) and 12.0 cm (4.7 in.) at sandy substrate stations.
Sediment depth had decreased (increased rod height)within seagrass patches and remained similar at
the sandy substrate locations since the Baseline Survey in January 2017.
In May 2018,sediment elevation was again monitored at the center rod of the 14 patches monitored for
bioturbation, in addition to the original 4 rods in sandy substrate.The center rod was not located (likely
due to burial) at 3 of the 14 seagrass patch locations and 1 sandy substrate location.The average height
of center rods in seagrass patches was 14.7 cm (5.8 in.) and 14.0 cm (5.5 in.) at sandy substrate stations.
Sediment depth has decreased (increased rod height)within seagrass patches and remained similar at
the sandy substrate locations since the Baseline Survey in January 2017.
Change in sediment elevation was computed among the replicate rods in each of the wave energy
reduction strata among all combinations of survey dates (Figure 8). In lieu of survey to survey changes
which revealed no clear pattern of change over time, comparisons with the first survey time were
performed. A one-way ANOVA revealed that only comparisons among Survey 1 and Surveys 5 and 6 had
differences in sediment elevation among Reference and the High wave reduction zone and Reference
and Low and High wave reduction zones (Table 4). Differences were driven by the sediment
accumulation in the High wave reduction zone,closest to the wavebreak. With the elimination of the
survey to survey comparisons a clear pattern of sediment accumulation across wave energy strata
emerged from this analysis. Sediment accumulated most in the High wave energy reduction zone closest
to the wavebreak with decreasing sediment accumulation with decreasing wave energy reduction and
distance from the wavebreak(Figure 8).This pattern has remained consistent among the surveys,
corroborating the near-field survey work(below).
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 28

Change in Elevation (ft) by zone
del ht 12 del ht 13 del ht 14 del ht 15 del ht 16
0.5 - - - 05 - - - 05 - - - 0.5 - -- 0.5 - - -
0.4 0.4 0.4 0,4 0.4
0.3 0.3 03 0.3 0.3
0.2 - 0.2. - _ - 0/ _ 0.2 0.2
0.1 - - 0.1 0.1 0.1 - 0.1
0.0 0.0 0,0 0.0 0.0
1 -0.1 _ -0.1 --0. -0.2 -0.2 _- -0. 3-gPT'
-0. 4rcs - -0.5 -05 -0.5 -05
W .0.6 -0.6. _ -0.6- _ _ -0.6 - _ -0,6
-0,1 -0.7 - -0.1 -0.7 -0.1 -
-0.8 - -0.8 -0.8. -0.8 -0.8• _
-0.9. -0,9 -0.9 -0.9 -0.9
-1.0 -1.0 -1.0 -1.0 -1.0
-1.1 -1.1 -1.1 -1.1 -1.1
-1.2 -1.2. _ -1.2 -1.2 -1.2
-1.3 -1.3. -1.3 -1.3 -1.3
4.4 -1.4 -1.4 -1.4 14
-1.5 -1.5 -1.5 -1.5 •1.5
1 M H 8 I. M H 8 1 N H 8 1 M H 8 1 M H R
Zone
Figure 8. Change in sediment elevation (del_ht in ft, MLLW) over time monitored at rods installed in previous bioturbation study. H=area of
high wave energy reduction by the wavebreak; M = medium; L= low; R= reference(no wave energy reduction). Error bars
represent±one standard deviation.The comparisons(e.g., 1_2, 1_3, etc. refer to comparisons among the first survey and
subsequent surveys.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 29

Table 4. One-way ANOVA testing differences in sediment elevation (ft, MLLW)from rods installed at
previous bioturbation patches between Survey 1 and subsequent surveys.
Survey 1= May 2016,Survey 2=January 2017,Survey 3 =October 2017,
Survey 4= May 2018,Survey 5=October 2018, Survey 6= May 2019.
Wave energy reduction Survey 1 4 2 Survey 1 4 3 Survey 1 4 4 Survey 14 5 Survey 1 4 6
Reference(none) ND ND R,H ND R,H
Low ND ND L,H ND L,H
Medium ND ND ND ND ND
High ND ND ND ND ND
Shaded bars=significant effect at P<0.05;comparisons with the same letters are not significantly different.ND=no significant
difference.Cells with no information represent strata where rods could not be located,presumably due to excessive sediment
deposition.R=reference,H=high wave energy reduction zone,M=medium wave energy reduction zone,L=low energy wave
reduction zone.
USV Digital Elevation Model:The USV collected bathymetry data across the entire site in June 2016
(Figure 9).The survey was conducted during both flood and ebb tides and real-time tidal corrections
were made to data collected.Water depths ranged from 0.7 to 1.6 m (2.3 to 5.2 ft) across the site. The
western portion of the site was notably shallower than the eastern portion. The USV will collect
bathymetry data during the final monitoring survey and data will be compared to this baseline
bathymetry.
wavebreak
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Figure 9. Track lines traveled by the Unmanned Surface Vehicle(black lines) and digital elevation
model at the Bonner Bridge Seagrass Mitigation Site prior to construction of the wavebreak
(ultimate location of wavebreak shown). Soundings are in MLLW.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 30

Near-field Wall Sediment Elevation Survey:The surveys conducted by SEPI revealed significant scour
pits having formed under the wavebreak units themselves.This sediment is suspected to be the source
of the light-colored band visible to the south of the wall in aerial images(Figure 3).The 5 transects were
treated as replicates for evaluating sediment elevation on both the north and south sides of the
wavebreak, by distance.A comparison of sediment elevations by distance and side of wall (north vs
south)shows a generally consistent pattern of erosion in the immediate proximity of the wall but with
little change in sediment elevation with distance on either side of the wavebreak(Figure 10).There,
transects on the south side of the wall however,generally appeared to be shallower. Upon examination
under 2-way ANOVA(Table 5)there was no significant interaction of the main effects(distance,side),
allowing each main effect to be re-tested independently.The effect of distance irrespective of side was
significant(p<0.05) at every survey time. However,the visually apparent difference in elevation among
the north and south sides of the wall was statistically significant beginning in January of 2018 and
remained different (but for April of 2018)through September of 2018,with the southern side being
consistently shallower. From October 2018 through March 2019 there was no significant difference in
sediment elevation among sides of the wall. Only in April 2019 (and May) did a significant difference
re-emerge with the south side being significantly shallower. In general, it was noted that the 0 distance
(immediately abutting the wall structure)was always the deepest,followed closely by the 5-foot
distance being the next deepest among all surveys (Figure 10).While statistically different,the elevation
differential among the north and south side was in the range of about 6 inches. Despite being shallower,
the south side was still within the range of seagrass growth as attested by the presence of numerous
seagrass patches within this near-field survey.
Table 5. Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey. Blue
shading indicates a statistically significant (p<0.05) difference. Blank cells have not yet been
surveyed.
Year 2017 2018
Month Jun Sep Jan Feb Mar Apr May Jun
Distance <.0001 <.0001 <.0001 0.0006 <.0001 <.0001 <.0001 0.0005
Side 0.7046 0.6983 0.0494 0.0011 0.0372 0.0608 0.0002 0.0002
Interaction 0.8913 0.9754 0.3347 0.777 0.118 0.0744 0.4098 0.8185
Year 2018 2019
Month Jul Aug Sept Oct Nov Dec Jan Feb
Distance 0.0025 0.0022 <00006 0.0006 0.0006 0.0002 0.0022 0.0086
Side 0.0029 0.0036 0.0042 0.5273 0.1684 0.0825 0.2117 0.1080
Interaction 0.9695 0.6937 0.9016 0.8492 0.9147 0.6512 0.4738 0.9404
Year 2019
Month Mar Apr May Jun Jul Aug Sep Oct
Distance 0.0024 0.0018 0.0010 - -- -- -- --
Side 0.2650 0.0151 0.0170 -- -- -- -- --
Interaction 0.8691 0.8486 0.7329 -- -- -- -- --
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 31

Panel 1
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0 5 10 15 20 25 30 35 40 45 50 75 100 dist II 0 5 10 15 20 25 30 35 40 45 50 75 100 did t
Figure 10. Panels 1-5; average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are± 1 standard
deviation.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 32

Figure 10. (Continued).
Panel 2
elevation_ft MEAN year=2018 month 2=3 elevation_ft MEAN year=2O18 mor1th r5
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0 5 10 15 20 25 30 35 40 45 50 75 100 dirt ft 0 5 10 15 20 25 30 35 40 45 50 75 100 did I
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CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 33

Figure 10. (Continued).
Panel 3
year=2019 month_2=7 year=2019 month_2=9
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CSA-N CDO T-FL-19-1830-2845-11-REP-01-FIN 34

Figure 10. (Continued).
Panel 4
year=2018 month 2=11 year=2019 moo h_2=1
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CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 35
10

Figure 10. (Continued).
Panel 5
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CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 36

WAVE REGIME AND MODEL VALIDATION
Long Term Wave Regime:After the wavebreak was installed, pressure sensors were installed at
specified stationary locations on both the north and south sides of the wavebreak to spatially assess
significant wave height(highest 1/3 of waves) distribution arising from the top 5% of wind events
between the two sides of the wavebreak. Figure 11 shows the difference in the significant wave heights
over elapsed time. During 2017,there did not appear to be a substantial difference in the significant
wave heights among the two sides,whereas in 2018,events where the significant wave height was
higher on the south side of the wall were more numerous and of greater difference over time.This
indicates that wave events were often higher on the south side than the north,suggesting that the north
side of the wall could also be receiving substantial sheltering from waves.
WEMo model validation:Wave forecast modeling using WEMo was initially conducted in January 2016
for different lengths of the wavebreak structure. Modeling was re-analyzed in January 2017 after
installation of the 500 ft (152 m)wavebreak (Appendix I).As done previously,the model was run on
65-foot (20-meter)grid cells, as the bathymetric data which are an important driver of the calculations is
not more resolved than that distance. Forecast acreage of seagrass was computed by regression from
the relationship of wave energy to seagrass cover(Fonseca and Bell 1998).The area of the seafloor
experiencing at least a 5% reduction in wave energy was computed.The total acreage associated with
the zones of wave reduction beyond the 5%threshold is given in Table 6.Theoretically,this could result
in an overall total of 1.78 acres (0.72 hectares)of new seagrass with the 10% reduction zone producing
1.13 acres (0.46 hectares)and the 5% reduction zone producing 1.50 acres (0.61 hectares).
Table 6. Areas for the wave energy reduction zones depicted in Appendix I in both acres and square
meters.
Percent Representative Wave Energy Reduction Square Meters Acres
>66% 3,184 0.8
33%to 66% 21,153 5.2
5%to 33% 200,889 49.6
<5% 1,095,260 270.6
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 37

DIFF IN WAVE HTS(M): POS VALUE = NORTH HIGHER while NEG VALUE = SOUTH HIGHER
0.15-
0.10- •
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12/12/2016 03/22/2017 06/30/2017 10/08/2017 01/16/2018 04/26/2018 08/04/2018 11/12/2018 02/20/2019 05/31/2019
Date
Figure 11. Difference in hourly significant wave heights (m) between and north and south side of the wavebreak structure for January 2017
through May 2019.A data gap(area of straight line)arose from need to reposition and recalibrate sensors. Positive values=wave
heights higher on north side; Negative values=wave heights higher on south side.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 38

f
After the model was run and a smoothing technique(krigging)applied (Appendix I), a disruption
appeared in the wave reduction just south of the wall. However, this is a product of the krigging and a
small zone of 33-66%wave reduction just south of the wall is a display artifact and was not part of the
acreage calculations.
EPIBIOTA MONITORING
During the January 2017 baseline survey, ebb tides were extremely low and monitoring stations at all
three elevation strata (high, middle,and low)were exposed above water. No biota had colonized the
substrate and the percent cover of concrete and rock were both 100% during this survey.
During the May 2018 survey,there was a consistent south/southwest wind that resulted in high water
levels at the structure,even at ebb tide. Monitoring stations at the high elevation were exposed above
water but were primarily wet and regularly splashed by waves hitting the structure during all tidal stages
observed.The middle elevation monitoring stations were exposed above water during all tidal stages
observed, also primarily wet, and regularly splashed by waves hitting the structure.The low elevation
monitoring stations were completely submerged at all tidal stages observed, even ebb tide. Due to high
levels of turbidity in the water column during the survey,the low strata monitoring stations were
photographed at a closer distance than the high and middle strata, requiring four close-up photographs
per station which were later mosaicked together.
During the May 2019 survey, ebb tides were relatively high. Monitoring stations at the high elevation
were exposed above water during all tidal stages observed but were primarily wet and regularly
splashed by waves hitting the structure (Photo 15).The middle elevation monitoring stations were
exposed above water during ebb tides, and regularly splashed by waves hitting the structure (Photo 16).
The low elevation monitoring stations were completely submerged at all tidal stages observed, even ebb
tide (Photo 17).
$Hdlpii-s 't ►,s&r .
•
• 4.*
•
•
Photo 15. Representative photo of rock substrate for a high elevation monitoring station (Station 27)
showing wet rock on the structure at the Bonner Bridge Seagrass Mitigation Site during the
2019 survey.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 39

•
Photo 16. Representative photo of concrete substrate for a middle elevation monitoring station
(Station 7)showing wet concrete, algae, and barnacle growth on the structure at the Bonner
Bridge Seagrass Mitigation Site during the May 2019 survey.
uA
9r i
•
Photo 17. Representative photo of concrete substrate for a low elevation monitoring station (Station 8)
showing submerged concrete and barnacle growth on the structure at the Bonner Bridge
Seagrass Mitigation Site during the May 2019 survey.
As in previous surveys,the percent cover of colonizing biota were assessed at the 60 fixed monitoring
stations along the wavebreak structure. Data was grouped first by substrate type (concrete or rock),
then by strata (high, middle, or low),and also by orientation (north or south side of the structure). Data
collected for concrete and rock monitoring stations are displayed in Tables 7 and 8, respectively.
Representative photographs of colonized substrate and motile fauna from the May 2019 survey can be
found in Appendix Ill.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 40

Table 7. Percent cover of biota from concrete monitoring stations during the Baseline Monitoring Survey in January 2017,the Year 2 Annual
Monitoring Survey in May 2018 and the Year 3 Annual Monitoring Survey in May 2019.Scaled color bars added for emphasis.
Concrete-North Concrete-South
Biota or Non-
Living Substrate 2017 2018 2019 2017 2018 2019
High IMiddlel Low High IMiddlel Low High 'Middle' Low High IMiddlel Low High IMiddlel Low High IMiddlel Low
Biota
Macroalgae 0 0 0 v.12 1111 U0.14 al bL 75 0 0 0 U14.51 U14.49 1116.81 RI ®.71 Ea
Barnacle 0 0 0 15.51 11161 13 I 2.84 f.26 E 15 0 0 0 0 6 7 in 0 F1.14 134.94
Hydroid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 16.64 0 0 0
Oyster 0 0 0 0 0.58 0 0.26 I 1.44 I 2.75 0 0 0 0 0 0 0 I 1.61 [ 8.8
Cyanobacteria 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
TOTAL BIOTA 0 0 0 13.63 9.3 3.6 az 33 W-- 0 0 0 [14.51 1E16 ME1 E�•�r ID r
Table 8. Percent cover of biota from rock monitoring stations during the Baseline Monitoring Survey in January 2017,the Year 2 Annual
Monitoring Survey in May 2018 and the Year 3 Annual Monitoring Survey in May 2019.Scaled color bars added for emphasis.
Rock-North Rock-South
Biota or Non-
2017 2018 2019 2017 2018 I 2019
Living Substrate 'Middle' 'Middle' l l l 'Middle' 'Middle'High Middle Low High Middle Low High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0 0 0 0 15.06 I 1.35 0 0 1112.94 0 0 0 0 0 I 1.41 0 Ei6.09 •.66
Barnacle 0 0 0 0 n11 134.86 [ 7 ®.53 1111.76 0 0 0 0 13.51 U6.9 0 [ 4.6 la.39
Hydroid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Oyster 0 0 0 0 0 0 0 F 7.84 IE.B.82 0 0 0 0 0 0 0 I 2.3 U-3.41
Cyanobacteria 0 0 0 0 0 0 0 I 4.9 V3 0 0 0 0 0 0 0 0 0
TOTAL BIOTA 0 0 0 0 F4.17 016.21 0 7 11.27 65 0 0 0 0 I 3.51 [18.31 0 [22.99 .46 I
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN 41

Colonizing biota observed on concrete substrate continued to include barnacles, macroalgae(primarily
unidentified green hair algae), hydroids, and oysters. For concrete stations, biotic colonization was now
dominated by macroalgae(versus barnacles in 2018)for the majority of strata. Percent cover of
barnacles declined as compared to the 2018 particularly in the low strata with maximum percent cover
down to 30.26% and 34.14%for the north and south sides, respectively(down from 64.03%and 73.0%
in 2018;Table 7). Percent cover of macroalgae increased since 2018, doubling or tripling its percent
cover in some cases. Macroalgae percent cover was greater than barnacles in all strata on both the
north and south sides, with a maximum percent cover of 78%for high strata on the north side and
75.57 on the south side.The small numbers of hydroids observed in 2018 were not found in 2019 while
oysters were now present in low cover in all strata on the north side and in the middle and low strata on
the south side with a high (south side, low strata) of 8.8%, a clear increase overall since 2018.
Colonizing biota on rock substrate included barnacles and macroalgae and new since 2018, oysters; no
hydroids were observed on either side of the structure. For rock stations, biotic colonization continued
dominated by barnacles for the majority of strata,with maximum cover of 24.39%on low strata on the
south side(Table 8). Unlike concrete, percent cover of macroalgae was generally low except for the low
south strata which had the highest percent cover(53.66%)of any biota across strata and side thus far.
For all elevation strata, concrete exhibited greater total colonization by biota versus rock on both north
and south sides of the structure, although the rock low strata on both the north and south sides were
becoming more equivalent to concrete. Unlike 2018 where both concrete and rock,the middle and low
strata generally showed greater colonization by biota than high strata, in terms of total biota all
concrete substrate strata on both sides were now becoming much more equivalent, however,with the
lowest strata still showing the highest percent cover of colonization. Rock colonization lagged behind
concrete percent cover of colonization especially for the high and middle strata, irrespective of side.
Only the rock substrate low strata, and particularly on the south side had become nearly equal to that of
concrete.
While there a clear trend of increasing colonization is occurring,there is non-systematic fluctuations in
cover among year, side and elevation strata,which is not uncommon for sessile intertidal communities.
Concrete is supporting more macroalgae and barnacles while rock is supporting more oyster
colonization. Hydroids and cyanobacteria continue to be rare, despite a pulse of cyanobacteria presence
in the rock low north strata this survey.
4.0 Conclusions
The wavebreak was successfully installed in January 2017 (Photo 18) and passed its post construction
engineering inspection. Monitoring will continue for an additional two years,through 2020(Table 1)
which will build off of this report.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 42

• Pik n -
? ° t t Apr
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w� rvMyti. y.
Photo 18. North-oriented view of the wavebreak installed in January 2017 at the Bonner Bridge
Seagrass Mitigation Site.The total structure length is 500 ft (152 m).
Seagrasses were successfully relocated from the construction corridor to two planting zones south of
the wall footprint in May 2016. Seagrasses in the area are composed of all three of the marine species
found in North Carolina (mixed H. wrightii, R. maritima,Z. marina). Seagrass cover measured within the
confines of natural, colonized seagrass displayed dramatic change from May 2016 to January 2017
(-42%).The relocated seagrass area showed a similar decline of-35.0%. It cannot yet be determined if
this change is a typical seasonal change in cover(spring versus winter) or if there was a contribution
from Hurricane Matthew.The hurricane passed over this area on 9 October 2016, prior to the
installation of the wavebreak structure;thus,the relocated area was highly exposed to an extreme wave
event only 5 months after planting which could have led to disruption of the relocated material. In
October of 2017 no seagrass was found in the randomly selected samples from both planting
areas. Subsequent surveys found cover ranging from 0.7 to 14.9%in the planted areas while during the
same time, cover in the reference areas ranged from 23.7 to 100%cover. At this point,the dramatic
fluctuation of cover among surveys in both the planted blocks and reference areas is likely the result of
storm impacts and a highly patchy and shifting seagrass distribution. Percent cover has thus far
averaged 8.3% in the planted areas and 47.1% in the reference areas.
A bioturbation experiment to help determine the relative role of bioturbation versus wave energy
reduction in seagrass space occupation was significantly disrupted by unknown sources. Only 20%of the
mesh (8 out of 40 remesh sheets)was relocated during the January 2017 survey.The wavebreak was not
present during this time so comparisons could only be tested among the remaining 8 remesh sheets and
those edges that did not receive remesh. There was no significant difference (p<0.05) among the
change in distance between the remesh and no remesh treatments, preliminarily indicating that
bioturbation was not strongly influencing the expansion of patch margins at that time. However,the
passage of Hurricane Matthew may have obscured effects (disturbance effects like Hurricane Matthew
erode seagrass patches from their edge, much like sting ray bioturbation; Fonseca et al., 2000).
Physical data collection of sediment elevation and wave energy has been completed.A digital elevation
model of the site was collected using the USV and these data will be compared with an end-of-project
survey conducted in the same manner to determine net sediment accumulation or loss in the project
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN 43

area. Sediment elevation stakes will also continue be monitored to gain an understanding of short-term
fluctuations in sediment elevation. An overall change in sediment elevation (-4.1 cm)was detected in
that survey which cannot be attributed to the wavebreak, as similar differences occurred across the
entire shoal.
More detailed monitoring of the near-field sediment elevation (within 150 feet)and the far-field (spread
over the entire wave energy forecast area) has shown a stable profile over time. With the near-field
monitoring,the south side has consistently been approximately Y2 foot shallower than the north but still
within the range of colonization by seagrass as is evidenced by the continued presence of seagrass in
this area, including the planting and reference sites.
The final wave modeling effort indicated that theoretically,the wavebreak influence on seagrass cover
could result in a total of 1.78 acres (0.72 hectares) of new seagrass overall,with the 10% reduction zone
producing 1.13 acres (0.46 hectares)and the 5% percent reduction zone producing 1.50 acres
(0.61 hectares).The classification resulted in 33.4 acres(13.5 hectares)seagrass cover across the Bonner
Bridge Seagrass Mitigation Site. Aerial imagery was collected and analyzed annually to capture changes
in seagrass cover associated with the addition of the wavebreak structure. That collection has been , y .
terminated as of April 2018 and has been replaced by monthly surveys under another contract. W `
Finally,time-zero data collection for epibiotic colonization was completed using a stratified random,
repeated measures design.As expected,there was no discernible epibiotic colonization in any of the
120 digital images recorded. Photographs of the exact locations on the structures,stratified by tidal
elevation and north and south sides of the wall will be repeated over time to quantify epibiotic
colonization trajectory, abundance and composition.The May 2018 data collection for epibiotic
colonization was completed using a stratified random, repeated measures design. During the May 2018
survey,the percent cover of concrete and rock decreased from levels observed in January 2017 as
epibiota colonized the structure. Concrete typically exhibited greater colonization by macroalgae and
fauna than the rock substrate.The middle and low strata of both concrete and rock showed greater
colonization than the high strata.
As of May 2019, a clear trend of increasing colonization continues with high levels of colonization among
all elevations of the wavebreak structure, irrespective of side (north or south facing). The most
frequently observed biotic cover on concrete portions has been macroalgae and to a lesser degree,
barnacles and oysters. Oyster colonization has only occurred on the lowest elevation strata of the
wavebreak structure.There are non-systematic fluctuations in cover among year, side and elevation
strata,which is not uncommon for sessile intertidal communities. Concrete is supporting more
macroalgae and barnacles while rock is supporting slightly more oyster colonization. Hydroids and
cyanobacteria continue to be rare, despite a pulse of cyanobacteria presence in the rock low north
strata this survey
This report occurs prior to the last survey(October 2019)of the twice-annual monitoring period of
performance. Beginning in May 2020, annual surveys and reports will only occur in the May—July
timeframe for the next two years to the end of the contract period.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 44

5.0 References
Bohnsack,J.A. 1979. Photographic quantitative sampling of hard-bottom benthic communities. Bulletin
of Marine Science 29:242-252.
https://www.researchgate.net/publication/233545259 Photographic Quantitative Sampling o
f Hard-Bottom Benthic Communities
Braun-Blanquet,J. 1972. Plant sociology:the study of plant communities. Hafner. New York, NY.
https://archive.org/details/plantsociologyst00brau
CSA Ocean Sciences Inc. 2017. B-2500 Bonner Bridge Seagrass Mitigation Site As-Built Report.
CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN.
Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near Beaufort,
NC, USA. Marine Ecology Progress Series 171:109-121.
Fonseca, M.S.,W.J. Kenworthy, and G.W.Thayer. 1998. Guidelines for the conservation and restoration
of seagrass in the United States and adjacent waters. NOAA COP/Decision Analysis Series.
222 pp. http://docs.lib.noaa.gov/noaa documents/NOS/NCCOS/COP/DAS/DAS 12.pdf
Fonseca, M.S.,W.J. Kenworthy, and P.E. Whitfield. 2000.Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biologia Marina
Mediterranea 7:373-376.
Fonseca, M.S., P.E. Whitfield, N.M. Kelly, and S.S. Bell. 2002. Modeling seagrass landscape pattern and
associated ecological attributes. Ecological Applications. 12:218-237.
Fourqurean,J.W.,A. Willsie, and C.D. Rose. 2001. Spatial and temporal pattern in seagrass community
composition and productivity in south Florida. Marine Biology 138:341-354.
http://seagrass.fiu.edu/resources/publications/Reprints/Fourqurean%20et%20a1%202001%20M
arine%20Biology.PDF
Kelly, N.M., M.S. Fonseca, and P.E. Whitfield. 2001. Predictive mapping for management of seagrass
beds. Aquatic Conservation Marine and Freshwater Ecosystems 11:437-451.
Kenworthy, W.J. and A. Schwarzchild. 1997.Vertical growth and short shoot demography in Syringodium
filiforme in outer Florida Bay, USA. Marine Ecology Progress Series 173:25-37. https://www.int-
res.com/articles/meps/173/m173p025.pdf
Kohler, K.E. and S.M. Gill. 2006. Coral Point Count with Excel extensions (CPCe):A Visual Basic program
for the determination of coral and substrate coverage using random point count methodology.
Computers and Geosciences 32(9):1,259-1,269.
Malhotra,A. and M.S. Fonseca. 2007. WEMo (Wave Exposure Model): Formulation, Procedures and
Validation. NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
https://repository.library.noaa.gov/view/noaa/9331
SEPI Engineering&Construction. 2016. Complete Construction Plans.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 45

Thayer, G.W.,W.J. Kenworthy and M.S. Fonseca 1984. The ecology of eelgrass meadows of the Atlantic
coast:A community profile. U.S. Fish and Wildlife Service. FWS/OBS-84/02.
https://www.nwrc.usgs.gov/techrpt/84-02.pdf
Townsend, E. and M.S. Fonseca. 1998.The influence of bioturbation on seagrass landscape patterns.
Marine Ecology Progress Series 169:123-132. https://www.int-
res.com/articles/meps/169/m169p123.pdf
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 46

Appendices
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 47

Appendix I
Project Site Selection
In 2015, CSA completed the process of site selection ([Report]Table 1). Existing seagrass cover and site
conditions were compared between potential mitigation sites within the Pamlico Sound in the vicinity
(^'8 km [^'5 mi]) of the Oregon Inlet.The Bonner Bridge Seagrass Mitigation Site was identified on a
historically stable shoal, where seagrass growth was evident,and had the most potential for increased
seagrass cover with gap closure among existing patches of the sites examined.The site was located near
dredge spoil islands approximately 4.8 km (3 mi) southwest of the existing Bonner Bridge at Oregon
Inlet. Wave and seagrass response models were utilized to determine the length of the wavebreak
forecast to achieve the 1.28 acres (0.52 hectares) of seagrass mitigation.
Also in 2015, CSA completed development of the wavebreak design and placement, a task which
required both wave forecasting, seagrass recovery forecasting and engineering sub consultation for
placement of the structure design. Wave forecast modeling(Malhotra and Fonseca, 2007)was utilized
to estimate the wave reduction effects of the wavebreak structure. Percent wave reduction was
computed from comparisons of no-wavebreak and wavebreak modeling scenarios for various length
wavebreak structures.The percent wave energy reduction for a given length wavebreak was converted
to percent seagrass cover(recomputed from Fonseca and Bell, 1998)to predict the overall increase in
seagrass acreage across the site as the result of wave reduction.The 500-foot (152-meter) long wall was
designed with an inverted "V-shape"consisting of two 250-foot(76.2-meter)sections.
The V-shape was a professional judgement on the part of the design team to mitigate wave impacts on
the wall from the forecast direction of maximum wave height development (northerly).Thus,the
wavebreak was oriented on the site to attenuate the dominant north and northeasterly exceedance
event(wind events composing the local top 5%of all hourly wind speeds, along with their direction,
over the preceding three years period)winds and create a calmer environment on the lee side (south
facing side)of the structure to promote seagrass patch coalescence and new, permanent seagrass
acreage.
Once the 500-foot(152-meter)wall length was selected by NCDOT(the wall length that most closely
approximated the forecast 1.28 acres [0.52 hectares] of new seagrass cover),four wave energy regimes
(treatments) were defined from a cumulative frequency analysis of the area covered by the modeling
effort where greater than 5% energy reduction was forecast to occur as the result of the wavebreak
(Figure I-1).The wave energy regimes represent high wave energy reduction (>66%forecast reduction),
moderate reduction (34 to 66%), low reduction (5 to 33%), and ambient or reference (<5% reduction).
These wave energy reduction regimes became strata for random selection of various sampling described
below.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN I-1

75°35'30"W 75°35'20"W 75°35'10"W 75°35'0"W
z
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500ft VVavebreak Structure
Percent RWE Reduction
▪>66%
33%-66%
5%-33%
▪<5%
75°35'30'W 75°35'20"W 75'35'10-W 75°35'01W 75°34'50"W
0 100 200 400 Meters
/1•4111114•11* I t + i I i i 110
CB A Coordinate System WGS 1984 UTM Zone 18N
Figure I-1. Post-construction forecast of wave energy(RWE; representative wave energy[J m-1 wave
crest]) based on 500-foot(152-meter)wavebreak structure, superimposed on image of
seagrass cover.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 1-2

Project Engineering and Design
CSA subcontracted SEPI Engineering to design the wavebreak and provide the engineering Signed and
Sealed Design Plans.The wavebreak was designed based on wave height forecasts provided by CSA
using the WEMo model (Malhotra and Fonseca, 2007)and the aforementioned exceedance event winds.
To meet the 500-foot (152-meter)design length,the structure was composed of 101 individual
"Reefmaker" units each containing a central piling, one concrete base unit, and three concrete wave
attenuator units stacked on the base unit and each embedded with natural granite rock to increase
surface area for epibiota colonization(each unit was 4.8 ft x 4.8 ft x 4 ft [1.46 m x 1.46 m x 1.22 m])
(Photos I-1 and 1-2). Granite rock was chosen to prevent bioerosion of the enhanced surface area. Each
Reefmaker unit had a bottom clamp and a top collar installed to secure the concrete layers to the
central piling to hold the base and wave attenuator units in a fixed vertical position on the piling,
preventing settling into the sand substrate over time.
1e
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Photo I-1. East-facing view of installation of the central pilings with piling clamps at the Bonner Bridge
Seagrass Mitigation Site.Yellow arrow points to an installed clamp.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 1-3

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Photo 1-2. One Reefmaker unit consisting of one base unit on the bottom and three wave attenuator
units containing granite rock. One hundred and one of these units were installed at the
Bonner Bridge Seagrass Mitigation Site. For scale,the width of the units is 4.8 ft (1.46 m).
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 1-4

Appendix II
Bioturbation Experiment
To evaluate the influence of biological disturbance on seagrass patches at the site (sensu Townsend and
Fonseca, 1998), CSA installed a bioturbation exclusion experiment in May 2016.There,40 locations were
randomly selected from within strata(10 per strata) defined by the forecasted wave reduction pattern
following wavebreak placement(high wave energy reduction =>66%; moderate reduction=34 to 66%,
low reduction =5 to 33%, and ambient or reference=<5% reduction) (Figure II-1).The nearest isolated
seagrass patch to that location was then selected for application of the experimental treatment.At the
center of all 40 patches, a 2.4-meter(8-foot) long stainless steel rod (Photo II-1)was driven into the
sediment until only 3 to 10 cm (1 to 4 in) remained above the sediment. Five randomly selected patches
were assigned wire mesh (wire remesh panels 1.07 m x 2.13 m [42 in x 84 in])welded steel wire remesh
sheet(with 0.106 m x 0.1.06 m [4 in x 4 in] mesh size)to exclude bioturbating sting rays and five were
un-protected within each of the four wave energy regimes (total of 40 patches).At each of two
randomly selected cardinal directions per patch,the distance from the center rod to the edge of the
seagrass was measured in centimeters using a metric tape (Photo 11-2). For patches receiving mesh, each
of the cardinal directions received a wire mesh.The longest length of the mesh was positioned parallel
to the patch edge approximately 1/3 on seagrass and 2/3 on sand to allow room for seagrass growth
(Photo II-3).Two J-shaped rebar stakes 0.3 m (1 ft) long anchored the mesh so it was flush on the
seafloor. Flush deployment on the seafloor and anchoring were performed to prevent entanglement by
sea life,such as diving birds. Other information recorded for each patch included the treatment received
(mesh or no mesh), elevation of the rod above the sediment, and seagrass species observed at each
edge. Change in the distance from the center rod to the patch margin will be recorded over time.The
statistical approach for this experiment is a repeated measures two-way analysis of variance with wave
energy and patch protection as main effects.The mesh and stakes will be removed and disposed of
appropriately when patch coalescence begins, at which time monitoring of these patches will cease.
During the May 2018 survey, scientists revisited each patch to collect data. Scientists navigated to the
location of the center rod using the Trimble GPS. Once on location,they searched for the center rod
using a glass bottom bucket and grazing a rake(tines up) on the seafloor.The distance from the center
rod to the edge of the seagrass patch was re-measured along the same cardinal directions established
during installation.The presence or absence of mesh,elevation of the rod above the sediment, and
seagrass species observed at each edge was also noted for each patch.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN Il-1

i
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Illi \\ \\\\ \
Photo II-1. Center rods (2.4 m [8 ft]) installed at each bioturbation experiment patch within the Bonner
Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 11-2

•
75°35.28"W 75'35'20"W 75°35.12"W 75°35'4'W
b Z
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�a ▪ Patches With Mesh
'51F- ' • Patches Without Mesh
• Sediment Elevation Control
"A;•- -500ft Wavebreak Structure
Percent RWE Reduction
"4 7 33%-68%
10%-33%
-<10%
75°35.20"W 75°3512"W 75°35.41W
0 100 200 400 Meters
0
CB A Coordinate System WGS 1984 UTM Zone 18N
Figure II-1. Randomized distribution of the seagrass patches and the experimental treatments
selected for use in the bioturbation study.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 11-3

� y
1111.1111411141111111116.
Photo 11-2. Scientists measuring from the center rod to the edge of the seagrass patch on the randomly
selected direction at the Bonner Bridge Seagrass Mitigation Site.
A +M A
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hb-
Photo 11-3. Exclusion mesh installed flush on the seafloor on the edge of the seagrass patch within the
Bonner Bridge Seagrass Mitigation Site. Mesh size is 0.106 m x 0.1.06 m (4 in x 4 in).
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 11-4

v ..
Bioturbation Experiment
At the time of setting out the experiment in May 2016,the average distance from the center rod to the
edge of all 40 patches was 3.8 m (12.5 ft) (Table II-1).At the onset of the experiment patches with
exclusion mesh had an average distance of 3.9 m (12.8 ft) and patches without exclusion mesh had an
average distance of 3.7 m (12.1 ft).
Table II-1. Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment. Updated July 2018; n/a = not applicable; meshes had been
removed. ND= no data;distances not measured as experiment had ended.
Survey All 40 patches(m) Patches with Patches without
exclusion mesh(m) exclusion mesh (m)
May 2016 3.8 3.9 3.7
January 2017 3.5 3.7 3.3
October 2017 1.48 n/a n/a
May 2018 ND ND ND
In January 2017, all 40 bioturbation patches were revisited and monitored. For all 40 patches,the
average distance from the center rod to the edge of the patch was 3.5 m (11.5 ft). For all mesh
treatment patches,the average distance to the edge of the patch was 3.7 m (12.1 ft) (however, mesh
was only located at 8 locations within 7 patches at the time of the survey). Patches without exclusion
mesh had an average distance of 3.3 m (10.8 ft). In October 2017,the number of monitored patches was
reduced to 14 to revisit only those 7 patches that still contained mesh at the time of the January survey
in addition to an equal number of non-mesh patches (n=7).Average distance from the center rod to the
edge of all 14 monitored seagrass patches was 1.5 m (4.9 ft). For the 7 patches that contained mesh at
the time of the January survey,the average distance to the edge of the patch was 0.5 m (1.6 ft).The
7 patches without exclusion mesh had an average distance of 1.9 m (6.2 ft). In October of 2017 the
experiment had been terminated and only the distance to patch edges were measured.That distance
had reduced from 3.5 to 1.48 m suggesting the dynamic nature of seagrass patch margins in this area.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 11-5

Appendix III
Representative Images of Biota — May 2019
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Image III-1. Blue crab (Callinectes sapidus) on wavebreak structure in the medium elevation strata.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN Ill-1

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f's
Image III-2. Hydroids colonizing the lower edge of the wavebreak structure. Note support piling in
background.
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN III-2

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Image III-3. School of juvenile fish utilizing the shallow water column over a dropped wavebreak unit.
Note the oyster colonization on the unit surface and discarded Neverita shell.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN 111-3

• 4
v
- ---
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Image III-4. Ruddy Turnstones roosting on top of the wavebreak structure.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN III-4

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Image III-5. Turf algae colonizing the concrete surface among embedded rocks on a medium elevation
portion of the wavebreak structure.
CSA-NCDOT-FL-19-1830-2845-11-REP-01-FIN Ill-S

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Image III-6. Oysters colonizing a rock on a medium elevation portion of the wavebreak structure.
CSA-NCDOT-FL-19-1830-2845-11-REP-0I-FIN 111-6

UAS Photogrammetry of the Bonner Bridge SAV
Mitigation Site — 2018 Summary Report
April 2019
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Prepared for: Prepared by:
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Rummel Klepper & Kahl CSA
900 Ridgefield Drive CSA Ocean Sciences Inc.
Suite 350 8502 SW Kansas Avenue
Raleigh, North Carolina 27609 Stuart, Florida 34997

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CSA
GSA Ocean Sciences Inc.
UAS Photogrammetry of the Bonner Bridge SAV
Mitigation Site - 2018 Summary Report
DOCUMENT NO. CSA-RK&K-FL-19-3324-02-REP-01-FIN
Version Date Description Prepared by: Reviewed by: Approved by:
01 03/01/19 Initial draft for review J. Pennell E. Hodel M. Fonseca
02 03/06/19 Revised draft J. Pennell M. Fonseca M. Fonseca
FIN 04/18/19 Final J. Pennell M. Fonseca M. Fonseca
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

Table of Contents
Page
1.0 Background 1
2.0 Methods 1
3.0 Results 4
3.1 TIME ZERO VERSUS 2018 SURVEYS 4
3.2 COMPARISONS BETWEEN 2018 MONTHLY SURVEYS 9
4.0 Interim Conclusions 9
5.0 Literature Cited 10
List of Tables
Table Page
1 Submerged aquatic vegetation (SAV) acreage results from GIS-based interpretation
of aerial imagery collected at Time Zero (January 2017) and August, September, and
October 2018 6
List of Figures
Figure Page
1 Overview of the Bonner Bridge wave-break submerged aquatic vegetation (SAV)
monitoring program study area showing the wave-break, representative wave
energy(RWE) reduction strata, and reference areas overlain on Time Zero imagery
from 1/17/2017 3
2 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from January 2017 (Time Zero)versus August 2018 for the Bonner Bridge
wave-break study area 11
3 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from January 2017 (Time Zero)versus September 2018 for the Bonner Bridge
wave-break study area. 12
4 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from January 2017 (Time Zero)versus October 2018 for the Bonner Bridge
wave-break study area 13
5 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from August versus October 2018 for the Bonner Bridge wave-break study area 14
6 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from August versus September 2018 for the Bonner Bridge wave-break study area 15
7 GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery
from September versus October 2018 for the Bonner Bridge wave-break study area 16
CSA-RK&K-FL-19-3324-02-REP-01-FIN

1.0 Background
In response to the loss of submerged aquatic vegetation (SAV) habitat caused by the replacement of the
Herbert C. Bonner Bridge over Oregon Inlet, North Carolina, a wave-break structure was constructed
with the purpose of experimentally modifying existing, patchy SAV habitat by attenuating wave activity
to test the ability of wave reduction to promote more continuous, persistent SAV coverage.The Bonner
Bridge wave-break structure was constructed and installed between November 2016 and January 2017.
In order to evaluate effects of the wave-break structure on the potential enhancement of SAV cover, a
long-term, aerial imagery-based SAV monitoring program was established,with baseline data collection
in January 2017 immediately following wave-break construction.The North Carolina Department of
Transportation (NCDOT) contracted Rummel Klepper and Kahl (RK&K) to lead this monitoring program.
CSA Ocean Sciences Inc. (CSA) was subcontracted by RK&K to support the monitoring survey design and
perform delineation of SAV cover from aerial imagery. This report presents the results of the aerial
photo interpretations performed thus far in the monitoring program,from datasets collected in 2017
and 2018.The aerial imagery-based SAV monitoring program is scheduled to continue through
December 2019.
2.0 Methods
The long-term SAV monitoring program for the Bonner Bridge wave-break structure includes delineation
of SAV cover from aerial imagery collected multiple times per year.The baseline aerial photos (Time
Zero)were collected in January 2017. Subsequent aerial photos were collected in August, September,
and October of 2018.This monitoring is continuing,with monthly aerial imagery collections scheduled
through 2019 with timing dependent on water clarity and other environmental conditions.This imagery
series will allow change analyses of SAV cover within a two-year period following wave-break
construction, which based on life history of the primary SAV species on the site (Halodule wrightii,
Ruppia maritima,Zostera marina) should encompass a time frame when responses by SAV cover could
occur(Kenworthy et al., 1982;Thayer et al., 1984; Fonseca and Bell, 1998).
The SAV delineation area includes the study area surrounding the wave-break and four
haphazardly-selected 2.5-acre reference areas (Figure 1)outside of but immediately adjacent to the
forecast zone of influence of the wave-break structure. The reference areas were situated to spatially
bracket the forecast area of wave energy effects and were placed without examination of their initial
SAV coverage. Specifically,the study area has been organized into the following strata based on an
estimate of the potential reduction in representative wave energy(RWE) caused by the wave-break
structure (Figure 1; See Table 1 for strata acreages):
1. >66% reduction in RWE (red zone);
2. 33-66% reduction in RWE (orange zone);
3. 5-33% reduction in RWE (green zone); and
4. Reference area (forecast as having less than a 5% reduction in RWE as the result of the position of
the wave-break structure).
Aerial imagery datasets of the study area were collected in January 2017 by CSA, and in August,
September, and October 2018 by RK&K, using Unmanned Aircraft Systems(UAS).The January 2017
imagery was collected using a Quadcopter DGI Inspire 1 UAS and mosaicked using a cloud-based
software.The 2018 imagery was collected using a DJI Phantom 4 Pro v2.0 UAS and also mosaicked using
a GIS-based software.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 1

CSA performed interpretation of aerial imagery datasets for the Bonner Bridge wave-break site using
geographic information systems (GIS). SAV cover was determined by classifying areas of SAV occurring
within the study area from georeferenced, high-resolution mosaicked aerial images. Each aerial image
had a resolution of 0.04 meters (m) (0.13 feet [ft]).The imagery was sometimes subdivided into
separate classification areas of interest (AOI) based on similar pixel spectral signature ranges, often at
the scale of individual image tiles(e.g., approximately 35 acres). Separate classification of each AOI
helped to eliminate variations in reflectance and environmental conditions across the entire study area
in order to reduce classification confusion.An unsupervised classification was then performed on each
classification AOI using a combination of iso cluster and maximum likelihood techniques using ESRI
ArcGIS 10.4 software.
After running the unsupervised classifications, each AOI was manually interpreted by denoting visually
apparent classes of SAV and classes of non-SAV (primarily seafloor substrate). Spectral noise and holes
within the classification results were removed and corrected using a combination of Esri® ArcMap
(10.6.1)tools including Majority Filter, Region Group, Set Null (enhanced boundary edges and removed
groups of small non-contiguous pixels that were smaller than a specified value), and Eliminate Polygon
Part(eliminated areas that were less than a specified value)tools in ArcGIS. Lastly, a manual
classification technique was then applied to the classification with guidance from a GIS analyst
experienced in SAV delineation and a SAV biologist with extensive experience in North Carolina SAV
systems.This consisted of removing areas of over-classification (classifying non-seagrass areas as
seagrass) and adding-in (digitizing) areas where under-classification (classifying seagrass as
non-seagrass) occurred, again based on visually apparent SAV cover in the imagery.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 2

75°35'24'W 75°35'121W 75°35'0'W 75°34'48'W
r r r
Nags Head
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z v
MI 500ft Wavebreak Structure n
Reference Area
• Percent RWE Reduction
. >66°/
33%-66%
5%-33%
r r 1 r
75°35'24'W 75'35'12-W 75°353:1 W 75'34'48 W
0 200 Feet
es**
C SA Coordinate System NAD 1983 StatePlane o 0 100 200 Meters
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North Carolina FIPS 3200 Feet 1 t t 110101
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Figure 1. Overview of the Bonner Bridge wave-break submerged aquatic vegetation (SAV)
monitoring program study area showing the wave-break, representative wave energy
(RWE) reduction strata, and reference areas overlain on Time Zero imagery from
1/17/2017. The wave-break structure is the light yellow line just north of the red zone.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 3

3.0 Results
3.1 TIME ZERO VERSUS 2018 SURVEYS
Percent cover of SAV for the Bonner Bridge wave-break study reference area, based on the GIS
classification of aerial imagery datasets yielded percent cover of 16.3%for January 2017, 10.8%for
August 2018, 19.9%for September 2018, and 19.0%for October 2018 (Table 1). The highest reference
area cover among all surveys was observed in September 2018.This was not unexpected based on the
timing of the survey at the end of growing season for Halodule wrightii in late summer.
In addition to percent cover of SAV at the time of each survey,Table 1 presents change analyses (gains
or losses of SAV in acres) performed between pairs of imagery datasets, along with a seasonal correction
for reference cover. Change in cover in the reference areas can be attributed to season alone, and
therefore the average absolute change per base acre of seagrass cover in the reference areas was
subtracted off the change per base acre of seagrass within each of the three RWE reduction strata.The
seagrass area per wave energy strata(>66%and 33-66%only), corrected for changes in reference area,
was then totaled.
For example, a comparison of the Time Zero (January 2017) survey to the August 2018 survey showed a
cover increase of 18.39%within the >66% RWE reduction strata. Adjusting for the-5.47% loss of cover
observed in the Reference areas (0.1839 x (1— [-0.0547]), resulted in a reference-adjusted value of
19.40%. Likewise, to determine the reference-adjusted total gain or loss of area within the>66% RWE
reduction strata, the absolute change of acres per base acre within the reference area was subtracted
from the change in area within that strata (0.16—[-0.05]) and resulted in 0.21 acre of gain.
Change analyses were performed for the following aerial imagery dataset comparisons:Time Zero
(January 2017) vs. August, September and October 2018. Disproportionately large increases in percent
cover were observed especially in the>66%and 33-66% RWE reduction strata (red and orange colored
strata, respectively; Figure 1) when compared to changes in the reference areas. When comparing Time
Zero with SAV cover in the>66%and 33-66% RWE reduction strata for the months of August, September
and October 2018 (19, 20 and 21 months following wave-break installation) a range of 13.8 to 22.2%
increase in SAV was observed or about 5 times more seagrass gained per unit seafloor in these two
strata as compared to reference areas (Table 1).The highest ratios of gain were seen when comparing
Time Zero with the September 2018 survey which is reasonable given that September is the time of year
likely to have the highest percent of SAV, meaning that any effect of the wave-break may be amplified in
that month.
Results of GIS-based interpretation of SAV cover for the Time Zero and August 2018 surveys are
displayed in Figure 2. When compared with the Time Zero survey (January 2017), the August 2018
survey showed an 18.2 to 19.4%increase in SAV cover(Reference-adjusted) in the>66%and 33-66%
RWE reduction strata, respectively(Table 1). From January 2017 to August 2018, SAV cover per base
acre in the >66% and 33-66% RWE reduction strata increased respectively 3.2 to 3.4 times more than
the reference areas.
During the August 2018 survey, only 12.74 acres of the total 50.44 acres comprising the 5-33% RWE
reduction stratum was delineated due to the quality of some of the aerial images.This resulted in the
reduced acreage of seagrass observed in August (6.41 ac).Therefore, the data for the 5-33% RWE
reduction stratum for August 2018 in Table 1 are a substantial underestimate. For this reason, any
comparisons discussed in this report that include the August 2018 data should exclude the 5-33% RWE
reduction stratum data.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 4

Results of GIS-based interpretation of SAV cover for the Time Zero and September 2018 surveys are
displayed in Figure 3. When compared with the Time Zero survey(January 2017), the September (2018)
survey showed a 6.9%to 22.2% increase in SAV cover (Reference-adjusted), depending on the RWE
reduction strata (Table 1). The increase in SAV cover was greatest within the >66% and 33-66% RWE
reduction strata, located closest to the wave-break structure.The smallest increase in SAV cover was
observed within the 5-33% RWE reduction stratum, located farthest from the wave-break structure.
From January 2017 to October 2018, SAV cover per base acre in the various RWE reduction strata
increased 2.0 to 6.3 times more than the reference areas.
Results of GIS-based interpretation of SAV cover for the Time Zero and most recent (October 2018)
surveys are displayed in Figure 4. When compared with the Time Zero survey (January 2017),the
October 2018 survey showed a 6.2%to 15.7% increase in SAV cover(Reference-adjusted), depending on
the RWE reduction strata (Table 1). The increase in SAV cover was greatest within the >66% reduction in
RWE reduction stratum, located closest to the wave-break structure.The smallest increase in SAV cover
was observed within the 5-33% reduction in RWE reduction stratum, located farthest from the
wave-break structure. From January 2017 to October 2018, SAV cover per base acre in the RWE
reduction strata increased 2.4 to 5.9 times more than the reference areas.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 5

Table 1. Submerged aquatic vegetation (SAV) acreage results from GIS-based interpretation of aerial imagery collected at Time Zero (January
2017) and August, September, and October 2018.
Areas of SAV Assessment Acres
Reference 9.88
>66%(red zone)polygon 0.87
33-66%(orange zone)polygon 5.16
5-33%(green zone)polygon 50.44
TIME ZERO VS.2018 SURVEYS
Time Zero(January 2017)vs.August 2018 (19 MONTHS)
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; Time Zero change or lost per times gain or
Aug'18 Cover Cover Jan'17 vs. adjusted Delta gain or loss of
area units are acres -Jan'17 (+=gain) Jan'17 Aug'18 Aug'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.61 1.07 -0.54 16.30% 10.83% -5.47% n/a -0.05 n/a n/a
>66%(red zone) 0.17 0.33 0.16 19.54% 37.93% 18.39% 19.40% 0.18 0.21 3.36
33-66%(orange zone) 1.17 2.06 0.89 22.67% 39.92% 17.25% 18.19% 0.17 0.94 3.16
5-33%(green zone)* 11.63 6.41 -5.22 23.06% 12.71% -10.35% -10.91% -0.10 -5.17 -1.89
Total area change(red+
1.16
orange)
Time Zero(January 2017)vs.September 2018 (20 MONTHS)
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; Time Zero change or lost per times gain or
Sept'18 Cover Cover Jan'17 vs. adjusted Delta gain or loss of
area units are acres -Jan'17 (+=gain) Jan'17 Sep'18 Sep'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.61 1.97 0.36 16.30% 19.94% 3.64% n/a 0.04 n/a n/a
>66%(red zone) 0.17 0.37 0.20 19.54% 42.53% 22.99% 22.15% 0.23 0.16 6.31
33-66%(orange zone) 1.17 2.36 1.19 22.67% 45.74% 23.06% 22.22% 0.23 1.15 6.33
5-33%(green zone) 11.63 15.24 3.61 23.06% 30.21% 7.16% 6.90% 0.07 3.57 1.96
Total area change(red+
1.32
orange)
CSA-RK&K-FL-19-3324-02-REP-01-FIN 6

Table 1 (Continued).
Time Zero(January 2017)vs.October 2018 (21 MONTHS)
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; Time Zero change or lost per times gain or
Oct'18 Cover Cover Jan'17 vs. adjusted Delta gain or loss of
area units are acres -Jan'17 (+=gain) Jan'17 Oct'18 Oct'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.61 1.88 0.27 16.30% 19.03% 2.73% n/a 0.03 n/a n/a
>66%(red zone) 0.17 0.31 0.14 19.54% 35.63% 16.09% 15.65% 0.16 0.11 5.89
33-66%(orange zone) 1.17 1.90 0.73 22.67% 36.82% 14.15% 13.76% 0.14 0.70 5.18
5-33%(green zone) 11.63 14.87 3.24 23.06% 29.48% 6.42% 6.25% 0.06 3.21 2.35
Total area change(red+
orange) 0.82
COMPARISONS OF SEQUENTIAL SURVEYS IN 2018
August 2018 vs.October 2018
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; change or lost per times gain or
Aug'18 Oct'18 Cover Cover Aug'18 vs. adjusted Delta gain or loss of
area units are acres (+=gain) Aug'18 Oct'18 Oct'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.07 1.88 0.81 10.83% 19.03% 8.20% n/a 0.08 n/a n/a
>66%(red zone) 0.33 0.31 -0.02 37.93% 35.63% -2.30% -2.11% -0.02 -0.10 -0.28
33-66%(orange zone) 2.06 1.90 -0.16 39.92% 36.82% -3.10% -2.85% -0.03 -0.24 -0.38
5-33%(green zone)* 6.41 14.87 8.46 12.71% 29.48% 16.77% 15.40% 0.17 8.38 2.05
Total area change(red+
orange) -0.34
CSA-RK&K-FL-19-3324-02-REP-01-FIN 7

Table 1 (Continued).
August 2018 vs.September 2018
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; change or lost per times gain or
Aug'18 Sep'18 Cover Cover Aug'18 vs. adjusted Delta gain or loss of
area units are acres (+=gain) Aug'18 Sep'18 Sep'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.07 1.97 0.90 10.83% 19.94% 9.11% n/a 0.09 n/a n/a
>66%(red zone) 0.33 0.37 0.04 37.93% 42.53% 4.60% 4.18% 0.05 -0.05 -0.50
33-66%(orange zone) 2.06 2.36 0.30 ( 39.92% 45.74% 5.81% 5.28% 0.06 0.21 -0.64
5-33%(green zone)* 6.41 15.24 8.83 1 12.71% 30.21% I 17.51% 15.91% 0.18 8.74 1.92
Total area change(red+
orange) 0.16
September 2018 vs.October 2018
Reference- Compared to
Acres gained reference,X
Percent Percent Delta%Cover Reference- adjusted total
Areas of SAV Assessment; change or lost per times gain or
Sep 18 Oct'18 Cover Cover Sep 18 vs. adjusted Delta gain or loss of
area units are acres (+=gain) Sep'18 Oct'18 Oct'18 %Cover base acre in acres in that loss per base
that zone acre in that
zone
zone
Reference 1.97 1.88 -0.09 19.94% 19.03% -0.91% n/a -0.01 n/a n/a
>66%(red zone) 0.37 0.31 -0.06 42.53% 35.63% -6.90% -6.96% -0.07 -0.05 -7.57
33-66%(orange zone) 2.36 1.90 -0.46 45.74% 36.82% -8.91% -9.00% -0.09 -0.45 -9.79
5-33%(green zone) 15.24 14.87 -0.37 30.21% 29.48% -0.73% -0.74% -0.01 -0.36 -0.81
Total area change(red+
-0.50
orange)
SAV=submerged aquatic vegetation
*The August 2018 delineation of the 5-33%RWE reduction stratum included only 12.74 acres of the entire 50.44 acres.This resulted in a reduced acreage of seagrass observed.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 8

3.2 COMPARISONS BETWEEN 2018 MONTHLY SURVEYS
Change analysis in SAV cover was performed between each survey in 2018 to measure short-term
changes in that cover:
• August 2018 vs. September and October 2018; and
• September 2018 vs. October 2018
These comparisons captured the seasonal dynamics of the SAV habitat. Comparisons of August and
October to September(the seasonal peak of reference bed cover) revealed general trends of cover
increase and decrease, respectively. Due to the incomplete delineation of the 5-33 % reduction in RWE
reduction stratum for the August 2018 survey,those results were not compared.
Results of GIS-based interpretation of SAV cover for the August and October 2018 surveys are displayed
in Figure 5. Between August and October 2018, SAV cover showed a 2.8 to 2.1% decrease
(Reference-adjusted), depending on the RWE reduction strata (Table 1). Both >66% and 33-66% RWE
reduction strata showed slight decreases in SAV cover. From August to October 2018, SAV cover per
base acre declined 0.3 times in the>66% RWE reduction stratum and declined 0.4 times in the 33-66%
RWE reduction stratum compared to the reference areas. Based on SAV growing season, SAV cover was
expected to start declining by October, as was observed in the>66%and 33-66% RWE reduction strata.
Results of GIS-based interpretation of SAV cover for the August and September 2018 surveys are
displayed in Figure 6. SAV cover in September was the highest observed among all surveys, across all
three RWE reduction strata.These high percent covers were expected as September was at the end of
the summer growing season. Between August and September 2018, SAV cover showed a 4.2%to 5.3%
increase (Reference-adjusted), depending on the RWE reduction strata (Table 1). Both the>66%and
33-66% RWE reduction strata showed slight increases in SAV cover. From August to September 2018,
SAV cover per base acre increased 0.5 to 0.6 times in the>66%and 33-66% RWE reduction strata closest
to the wave-break compared to the reference areas.
Results of GIS-based interpretation of SAV cover for the September and October 2018 surveys are
displayed in Figure 7. Between September and October 2018, SAV cover decreased in all three RWE
reduction strata, between 0.7%and 9.0% (Reference-adjusted) (Table 1). This decrease was expected
due to the declining growth of SAV following the end of the summer growing season. SAV cover per base
acre in the RWE reduction strata decreased from 0.8 to 9.8 times when compared to the reference
areas.The decrease was more drastic for the >66%and 33-66% RWE reduction strata.
4.0 Interim Conclusions
The preliminary change analysis results comparing the Time Zero survey in January 2017 and the most
recent survey in October 2018 indicate that the wave-break structure is functioning as intended and is
facilitating a seasonally variable increase in SAV cover within all three RWE reduction strata, particularly
those two strata closest to the wave-break (>66%and 33-66%). Aerial imagery collections and
interpretations are scheduled to continue monthly through 2019 and will be assessed in conjunction
with the 2017 and 2018 surveys, which will provide a robust dataset for evaluating the effect of the
wave-break structure on the surrounding SAV landscape as part of the long-term Bonner Bridge SAV
mitigation site monitoring program.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 9

5.0 Literature Cited
Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near Beaufort,
NC, USA. Mar. Ecol. Prog. Ser. 171:109-121.
Kenworthy, W.J.,J.C. Zieman, and G.W. Thayer. 1982. Evidence for the influence of seagrass on the
benthic nitrogen cycle in a coastal plain estuary near Beaufort, North Carolina (USA). Oecologia
54:152-158.
Thayer, G.W.,W.J. Kenworthy, and M.S. Fonseca. 1984. The ecology of eelgrass meadows of the Atlantic
coast: a community profile. U.S. Department of the Interior, Fish and Wildlife Service, Division of
Biological Services, Research and Development, National Coastal Ecosystems Team.
FWS/OBS-84/02. 147 pp.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 10

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CSA-RK&K-FL-19-3324-02-REP-01-FIN 11

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CSA-RK&K-FL-19-3324-02-REP-01-FIN 12

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CSA-RK&K-FL-19-3324-02-REP-01-FIN 13

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Figure 5. GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery from
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CSA-RK&K-FL-19-3324-02-REP-01-FIN 14

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CSA-RK&K-FL-19-3324-02-REP-01-FIN 15

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Figure 7. GIS-based submerged aquatic vegetation (SAV) interpretation from aerial imagery from
September versus October 2018 for the Bonner Bridge wave-break study area.
CSA-RK&K-FL-19-3324-02-REP-01-FIN 16

Brittingham, Cathy
From: Herring, Kathy
Sent: Wednesday,January 02, 2019 8:53 AM
To: Staples, Shane
Cc: Brittingham, Cathy; Huggett, Doug; Stanton, Tyler P; Cox, Marissa R
Subject: RE: [External] RE: Bonner Mitigation presentation
Yep,that is the plan. We started the drone work this past Spring so going forward we will have month to month comparisons.
Thanks!
Kathy
From:Staples,Shane
Sent:Wednesday,January 02, 2019 8:30 AM
To: Herring, Kathy<[e-mail]>
Cc: Brittingham, Cathy<[e-mail]>; Huggett, Doug<[e-mail]>;Stanton,Tyler P
<[e-mail]>; Cox, Marissa R<[e-mail]>
Subject: RE: [External] RE: Bonner Mitigation presentation
Thanks, in the future with more sampling seasons available I would hope they may start using same season comparisons if for no
other reason that ease of data comparison.
Shane
Shane Staples
Fisheries Resource Specialist
Division of Marine Fisheries
North Carolina Division of Environmental Quality
252-948-3950 office
Shane.staples([e-mail]
943 Washington Square Mall
Washington, NC 27817
From: Herring, Kathy
Sent: Monday, December 31, 2018 10:08 AM
To:Staples,Shane<[e-mail]>
Cc: Brittingham, Cathy<[e-mail]>; Huggett, Doug<[e-mail]>; Stanton,Tyler P
<[e-mail]>; Cox, Marissa R<[e-mail]>
Subject: FW: [External] RE: Bonner Mitigation presentation
Hi Shane, Hope you had a great Holiday! Yours was the only question that I have received, so here is Mark's answer.
Thanks!
Kathy
From: Fonseca, Mark<[e-mail]>
Sent: Wednesday, December 19, 2018 3:02 PM
To: Herring, Kathy<[e-mail]>
Cc: Hodel, Erin<[e-mail]>
Subject: [External] RE: Bonner Mitigation presentation
1

CAUTION: Report Spam.
Erin and I developed this response:
Kathy,
That is a very good question—and fortunately one that we considered in assembling the data. Recall that I mentioned speaking
with my friend Don Field at NOAA about this very problem; comparing cover from January when we know above-ground
seagrass biomass is reduced, especially for Halodule,with September imagery when aboveground biomass is probably at a
yearly high for that species.
Long answer: We considered two options. One was to utilize mid-season imagery to help us manually fill in cover on the large
patches which are a substantial source of difference in areal coverage among seasons. In January,those big patches look like
halos as only the edges are heavily vegetated, largely with Zostera, which needs that slightly deeper margin of a
patch. However, in and around September what appeared to be unvegetated cover in the center of the patches appear heavily
vegetated as a consequence of Halodule emergence. Two problems prevented us from taking that approach: 1)small
differences in rectification of the images prevented straight pixel to pixel comparisons of cover which would have helped the
manually filling process and 2) there were just too many patches!
The second option and that which was used in the presentation was to use references sites to control for changes in cover
among seasons and years. This much more parsimonious approach circumvents the rectification issue as we are just comparing
the amount of cover in large areas: the 4, 2.5 acre reference sites versus the high and moderate wave energy reduction zones,
irrespective of exactly where the cove was on the seafloor within those areas.
The reference areas (selected to be just outside the forecast wave energy reduction zones,these 4 sites were arbitrarily placed
without looking at the seagrass imagery and only the wave forecast zones so that we would not be biased by seagrass
abundance in their placement)on average increased their cover—4%when comparing the January 2017 and September 2018
images. Therefore, we reduced the seagrass acreage totals in both of the wave energy reduction zones by 4% before comparing
change in cover among the two time periods and before computing percent changes. Thus we used the reference to control for
among year and season changes.
We will also be comparing cover among all combinations of seasons to see if there is a discernible trajectory in this
change. However,even if we do not see a trajectory,we will look for consistency/stability in cover levels. A trajectory may not
emerge because of the nature of the threshold response of seagrass cover to a change in wave energy; i.e., once the wave
energy at a site crosses the threshold,the response may be rapid and not a nice steady climb over seasons or years. I have
personally witnessed large-scale and very rapid shifts in seagrass cover in the NC system (both +and -; for+see Fonseca et al.
1990)therefore my expectation for capturing a nice steady increase in seagrass cover to a new stable state of higher cover is
tepid at best.
A short answer: Yes, this could happen—so we used change in cover in the reference sites over this same time period to correct
the change in seagrass cover. Here,this was a 4% reduction in the wave-affected areas in September of 2018 because the
Reference sites increased 4% between Jan 2017 and Sept 2018.This consequently decreased the change in cover and this
reference, down-adjusted percent change was what we reported.
Please let us know if this suffices and if there are other questions or needs for clarification.
Best,
Mark
Mark S. Fonseca, Ph.D.
CSA Ocean Sciences Inc.
Vice President, Science
[e-mail]
2

Direct: [phone]
Cell: [phone]
From: Herring, Kathy<[e-mail]>
Sent:Wednesday, December 19, 2018 9:03 AM
To: Fonseca, Mark<[e-mail]>
Cc: Hodel, Erin<[e-mail]>
Subject: FW: Bonner Mitigation presentation
This is the only question I have received.
From: Staples, Shane
Sent: Friday, December 14, 2018 10:10 AM
To: Herring, Kathy<[e-mail]>
Subject: RE: Bonner Mitigation presentation
Thanks, one thing I didn't catch yesterday that would be good to clear up on slide 19 in what time of year the SAV increase was
based on. In theory you could gain a lot of SAV coverage from January to September just based on growing season.
Shane
Shane Staples
Fisheries Resource Specialist
Division of Marine Fisheries
North Carolina Division of Environmental Quality
252-948-3950 office
[e-mail]
943 Washington Square Mall
Washington, NC 27817
From: Herring, Kathy
Sent: Friday, December 14, 2018 9:49 AM
To: Harris, Philip S<[e-mail]>; Cox, Marissa R<[e-mail]>; [e-mail]
<[e-mail]>; "Lucas, Ron" <[e-mail]>; Wilson,Travis W. <[e-mail]>; Bryan,
Roger D<[e-mail]>; Brittingham, Cathy<[e-mail]>; [e-mail]; Dagnino,
Carla S<[e-mail]>; Donnie Brew<[e-mail]>; Huggett, Doug<[e-mail]>; Euliss,
Amy<[e-mail]>; Gary [e-mail]; Daisey, Greg<[e-mail]>; Staples,Shane
<[e-mail]>; Lane, Stephen<[e-mail]>; Chambers, Marla J
<[e-mail]>; McLendon, Scott C SAW<[e-mail]>; Mellor, Colin
<[e-mail]>; Pair, Missy<[e-mail]>; Paugh, Leilani Y<[e-mail]>; Williams, Paul C
<[e-mail]>; Gledhill-earley, Renee<[e-mail]>; Rivenbark, Chris<[e-mail]>;
Shern,James F<[e-mail]>;Tom Steffens<[e-mail]>; Matthews, Monte K SAW
<[e-mail]>; [e-mail]; Mason,Suzanne<[e-mail]>;
McHenry, David G <[e-mail]>;Werner, Christopher M <[e-mail]>; Somerville,Amanetta
<[e-mail]>; Morgan,Stephen R<[e-mail]>; Ward, Garcy<[e-mail]>; Smyre,
Beth<[e-mail]>; Weaver, Derrick G <[e-mail]>; [e-mail];
'[e-mail]' <steve d [e-mail]>; McCann, Nora A<[e-mail]>
Cc:Tortorella,James<[e-mail]>; Stanton,Tyler P<[e-mail]>; Hodel, Erin <[e-mail]>;
Fonseca, Mark<[e-mail]>; Hernandez, Pablo A<[e-mail]>
Subject: Bonner Mitigation presentation
All,
3

Brittingham, Cathy
From: Herring, Kathy
Sent: Friday, December 14, 2018 9:49 AM
To: Harris, Philip S;Cox, Marissa R; [e-mail]; "Lucas, Ron"; Wilson, Travis W.;
Bryan, Roger D; Brittingham, Cathy; [e-mail]; Dagnino, Carla S; Donnie Brew;
Huggett, Doug; Euliss, Amy; [e-mail]; Daisey, Greg; Staples, Shane; Lane, Stephen;
Chambers, Marla J; McLendon, Scott C SAW; Mellor, Colin; Pair, Missy; Paugh, Leilani Y;Williams,
Paul C; Gledhill-earley, Renee; Rivenbark, Chris; Shern, James F;Tom Steffens; Matthews, Monte
K SAW; [e-mail]; Mason, Suzanne; McHenry, David G;Werner,
Christopher M; Somerville, Amanetta; Morgan, Stephen R;Ward, Garcy; Smyre, Beth; Weaver,
Derrick G; [e-mail]; '[e-mail]'; McCann, Nora A
Cc: Tortorella,James; Stanton, Tyler P; Hodel, Erin; Fonseca, Mark; Hernandez, Pablo A
Subject: Bonner Mitigation presentation
Attachments: 2018Annual_Status_Update_BBMit.pdf
All,
As requested, attached is a copy of the status update of the Bonner Bridge SAV mitigation project presentation. If you have any
comments or questions please send them to me, I will compile, and get answers back to you.
Thank you,
Kathy
Email correspondence to and from this sender is subject to the N.C. Public Records Law and may be disclosed to third parties.
1

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CSA Ocean Sciences Inc.

Oft M
Conclusions
• Seagrass coverage changes across disturbance gradients
• NC seagrass/disturbance well studied and modeled
• Manipulation of gradient = changes in seagrass coverage
• Reefmaker method with suspended wavebreak structure :
— Supported new, persistent seagrass cover
— Provided substantial additional Essential Fish Habitat services
• Cautiously optimistic - seagrass acreage > mitigation requirements
— Needed 1.28 acres
— + 1.34 in just the two highest wave reduction areas
— + 4.8 acres if the total area of > 5 % forecast wave energy 1, is considered
• Continued monitoring to validate and improve forecasting
2k*
CSA
CSA Ocean Sciences Inc.

RESULTS Seagrass Cover — preliminary assessment
January 2017 ..w� , �, :. September 2018 Reference
i;l * . .. ~ � '� Zones
•
•
t. •%• Y , .A7 of , • $ ,,,r ,,r .,dt 1ta R. --.. . *••
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t, �aa 5o ri.,• .� ri 0 •.
.f ;. ;' ; -,r £ �` r �,, °�� ��; >66% energy 1
r s 14 firo 'e% ,ta, i +iis fa �4
i • '1, �' 33 66% ener9Y
•yam•. ,,, ` Mr : .��yy • :♦ _•; '• 1 4 • i'i 'it • _ _
ottr
tY �i°'.-.1.,.1'ti(� ! r'; * 'r" •s ~ .^ +, r ;�.• firy', ^�•'4 `S A a ` k t�• v'- +�.I •�
lep
t rat it *, `}� •q\ 72+t tiV a F ,• • . . ol I' [ . + °
ti ' *, ,i -s 1*1. 4,;,, ,.i k!,/k,lc ' ' ' - - 'ial... ,.14' 3 .4 ;* 4,,),r j t ' 1A .,1,, 5-33 /° energy 1
ie,
t 1• o r" ' ,4* :** i it ,,44:i 'T'r to A � "'V .*.t .. .aAs ••rt hi r AI' -' - 14. '''' ..'• , ,r, ,,, 4, a?� 7�- a �•i C���F�rylp
" + 1 .34 acres in zone >33% energy
+ 4.82 acres in zones with > 5% energy,
Areas of assessment Gain per base acre % cover 2017 % cover 2018 LI % cover Ref. adj. A % cover
Reference areas (9.8 ac) 0.22 16% 20% Q 4%
Total area of > 66% FP 1.18 L 20% 43% 23%
Total area of 33-66% , 1.02 23% 46% 23% 18%
Total area of 5-33% 1 0.31 P 21% I 30% Li 7% 1E1 6%
CSA Ocean Sciences Inc. CSA

RESULTS Epibiont Cover/Relocated Seagrass
., . ,
,...
, , Substrate % Infrequent Frequent
Near-
•
- _' Cover Inundation Inundation continual
Inundation
-
. yg. Embedded
.r 0 19 17
. •' Granite Rock
y ., T .�
e «
. Concrete Base 27 70 90
abhor-' k If.. .**.1.4 ' 40.'''`'
Concrete base . 1.
�'
\ b
-�-15% areal cover relocated - ' - y_
sea grass as of October 2018 survey .�' 2
/it*
CSA
CSA Ocean Sciences Inc.

RESULTS Sediment elevation survey
2500 BONNER BRIDGE SAV MITIGATION - PILING 51
NOTE.DATA WAS GATHERED IN THE FIELD
WITH LEVEL AND ROD.ELEVATIONS ARE
REFERENCED FROM AS-BUILT BENCH MARK
DATA COLLECTED:June 2017 to September 2018 ELEVATIONS.
SCALE
b I'=2.5'VERTICAL e
I'=25'HORIZONTAL
7 '
6
4
a
3
BOTTOM OF DISK ELEVATION = -2.05
1 I
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150 125 100 80 60 40 20 0 20 40 60 80 100 125 I 0 W =p '
v, us 1
o A
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F
JUNE BASELINE SURVEY 2017 FEBRUARY TOPOGRAPHIC SURVEY 2018 MAY TOPOGRAPHIC SURVEY 2018 ----AUGUST TOPOGRAPHC SUH'VEY 1OIb
SEPTEMBER TOPOGRAPHIC SURVEY 2017 MARCH TOPOGRAPHIC SURVEY 2018 JUNE TOPOGRAPHIC SURVEY 2018 - SEPTEMBER TOPOGRAPHC SURVEY 2018 `J/v . 1
JANUARY TOPOGRAPHIC SURVEY 2018 APRHL TOPOGRAPHIC SURVEY 2018 JULY TOPOGRAPHIC SURVEY 2018 \�
dS*At
CSA Ocean Sciences Inc.

RESULTS Sediment elevation survey
• Transect surveys of sed elevation
-„,.....�. • Erosion pits under structure
ti,4y,,
• Shoaling on south (lee) side
MO
OM
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of
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ISM
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2
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rr�
rr
' north south north south north south north south north south
UP" " , " 50 75 1h 125 150
rr
row
CSA
CSA Ocean Sciences Inc.

Wave brea k status
• Some (" 10%) of the collars
slipped and now sit on sand A.
• This is being carefully monitored --
• Wave attenuation still occurs in - - ". :r �.,: .._
these gaps - iiiiii, I,* . , • ,> J.
• No visually apparent response of - — - -.� �. . _ : - ;
seagrass cover or sediment ty - `�
yr. �' `•. _
elevation in association with the -
slipped units
• Additional unit layers may be
added0014040,,_. - r�� ,��; � - "
,..+� le. 'u ' is e
tia
o
CSA
CSA Ocean Sciences Inc.

I-
RESULTS Full installation and Monitoring
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Installation Dec 2016 Jan 2017
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CSA Ocean Sciences Inc.

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APPROACH Sea grass enhancement location and strategy
gv
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Dredge material islands Y i
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Bonner Bridge
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CSA
CSA Ocean Sciences Inc.

BACKGROUND Recent model validation
_ .
Laningt Moat
a tl.ar10.1W74101FW60'n . CronMarl
(a)
Physical drivers of seagrass spatial configuration: the role
of thresholds o r stic
Amy V.Uhrlsp•Monies(:.Turner { �_ .., •• ��t
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0 This J4lne Ivern*sagged t worts Jo a.ten 11nN
adj —
er red v.r U.S. ropyri ht wuA N u*ea r,nu aM1lau I��.,pyngM pruu.mn n dv l,naeJ araa hw,era,u.OSI may R
abysm o,heap cp$ngm M.A.201$
Ah!rani rapunee cal thew scones to wave energy,tidal coral 0 ••
Craneu Seagram landscape*vary.uabtalndly in need.arid water depth a 62 eyuarule.Ito In North ' ] Q
extend and pattern.mauling from depth umarnm and Carols-la,USA Seagram*landwape•were momenta-
hydrodynamic �•/ Q
alias gradients and nary cahibu observedm
live of cover type.observed in the estuary vr�rn y generated / i
threshold behavior in response to changes in physical by wave energy. • .
dnvas. Seagram ladvcapa pant in a deacate W./0Portent cover,patch eon,and number of •
Threshold balance Nance.pnresaca of divurbance and m emo- patches all M n clined with ineaung ware meter. �` •
cry and therefore may exhibit behavior typical of le d a havua ia:wrn wave energy change fU■/1
classic critical system*. pants letween 675-774 J m .Seagmas landscape* O 0
f/birclla<.d tldarnue Rwr hydnddynnnic dnvas and dillne d In 4at1al con igwalum and physical*clang,
phy.ucal selling mlluende sear..N N du:ape cnrgar. above*nod heklw change points.There ww mratme L 1111.
noom and d:unligumadn.Deemum of*eagnw*patch suppat los a power law relationship tot pitch ore •
sit h.-Minim.typify paten obhavd fin ennui! demhuuon r nos a wide range cal sedan.*landwape
•
.yaeno cover and muse energy.
•
Mrrhak We used llandscapenmean.to 4mntdy tie Crmr lwurnr v With weather attunes on the sae.
**glottal configuration of neagrws and then Modeled the much of thu aruatine stags,will b Ae canned to Q
ncreu ar
ad wave energy.Where teapot eus Jut •
parbwneag/�twllny ntMehi The online vealond below the ware energy change you..Immature
new
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air oxide rimer ,Jgne.lal ranch f091R1aain, grin ru wave nitic d tin nit a
Iaim wyplsaoy�rerol wean is naldR m auRvirM stable sYle of down weer resulting in Ier cover •
410
men uveng in the atuany. ` •
A V.the r®a Seagram Spatial cosh * • ! '
Mann Dana Divas..Dpamce or(:a..me heywerconfiguration
Nam,Oceanic and Annaplw.Adrmnaam. Hydrodynamic* hcnlognca!thresholds Allenale
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yubailc'Woe.Id 4menter N IS osr..irRWE (joules/m wave crest) ,
• Uhrin and Turner 2018
• Survey of 63 NC seagrass beds
• Stratified sampling f(wave energy)
• Threshold response of seagrass cover to wave energy
r**
CSA
CSA Ocean Sciences Inca

�" 4.. �« = Tipping points in NC sea grass
pp g g s cover
, '' Recomputed using RWE (from Fonseca and Bell, 1998).
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0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 190
REPRESENTATIVE WAVE ENERGY (Joules m-1 wave crest)
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CSA
CSA Ocean Sciences Inc.

BACKGROUND Examples of seagrass response to E energy: Back Sound, NC
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CSA Ocean Sciences Inc.

BACKGROUND Examples of seagrass response to A energy: Snake Creek, TX
2008
2012
^r.
I
Google earth
1951 Imagery Date 11/28/2011 20°09'46 76°N 95°01'59.77"W elev 0 R eye alt 3444 ft 0
CSA
CSA Ocean Sciences Inc.

BACKGROUND Seagrass landscapes change across disturbance gradients
Increasing currents waves bioturbation
(disturbance extent, intensity, duration, frequency, sequence)
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CSA
CSA Ocean Sciences Inc.

BACKGROUND Bonner Bridge Seagrass Impacts
• Bonner Bridge - direct connection of OBX to
mainland , in disrepair and being replaced
• 1 .28 ac seagrass were forecasted to be impacted by
the replacement bridge
• No nearby seagrass beds needing mitigation
• Existing understanding in NC of wave energy
seagrass landscapes
• Here: project to produce new, permanent seagrass
acreage through wave energy manipulation on
existing , patchy seagrass habitat
4,1k
CSA Ocean Sciences Inc. C'S

OF NORTH e4
9
O
m 2
CSA4�4,,OF TRAN�'e0
t - Bonner Bridge
- }
- .,,.►A.-.,...
� � - a � Enhancement Update
. . . - "� _ a ' ram `^ : ..
13 December 2018
Dr. Mark Fonseca & Erin Hodel — CSA Ocean Sciences
Kathy Herring - NCDOT
CSA Ocean Sciences Inc.

ei I el. *
CSA
CSA Ocean Sciences Inc. www.csaocean.corn
8502 SW Kansas Avenue Phone: [phone]
Stuart. Florida 34997 Fax: [phone]
19 November 2018
Kathy Herring
North Carolina Department of Transportation
Project Development and Environmental Analysis Unit
Natural Environment Section
1598 Mail Service Center
Raleigh, North Carolina 27699-1598
Subject: Summary of Year 2 Biannual Survey—October 2018—LETTER REPORT
Dear Kathy:
CSA Ocean Sciences Inc. (CSA) conducted the second Biannual Monitoring Survey (Year 2) for the Bonner
Bridge Seagrass Mitigation Site from 6 to 8 October 2018.The passing of Hurricane Florence on
September 14, 2018 in southern North Carolina appeared to have resulted in both below and
above-normal water levels and increased turbidity at the Bonner Bridge Seagrass Mitigation Site during
and for several weeks after the storm (J. Hall and W. Silver, pers comm.; preliminary analysis of water
level data from on-site sensors). However, water levels and turbidity appeared normal at the time of the
survey.Table 1 lists CSA's previous activities and future scheduled surveys that encompass the
long-term seagrass monitoring program for this project.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation Experiment Initiation May 2016 Complete
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 Nov. 2016 to 18 Jan. 2017 Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan. 2017 Complete
Year 1 Biannual Monitoring Survey 2 to 4 Oct. 2017 Complete
Year 2 Annual Monitoring Survey 13 to 17 May 2018 Complete
Year 2 Biannual Monitoring Survey 6 to 8 October 2018 Complete
Year 3 Annual Monitoring Survey May 2019 Scheduled
Year 3 Biannual Monitoring Survey October 2019 Scheduled
Year 4 Annual Monitoring Survey July 2020 Scheduled
Year 5 Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.

The Year 2 Biannual Monitoring Survey included:
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation; and
• Inventory and maintenance of epibiota monitoring stations on the wavebreak structure.
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina; September 2015) referenced in the
permit (Permit Modification No. 106-12)to ensure all monitoring requirements were met.
During the October 2018 survey, scientists observed patchy seagrass habitat consisting of two species of
seagrass (Halodule wrightii and Zostera marina). Halodule wrightii was the most prevalent species,
followed by Z. marina. Ruppia maritima, as distinguished by presence of flowering shoots, was not
observed during this survey. The major substrate type observed throughout the site was fine sand.
Limited vessel traffic was observed within the immediate vicinity of the wavebreak structure.
Site conditions were relatively consistent during the survey,with slight variations due to direction and
strength of the wind. Average daily water temperatures during the survey ranged from 25.7°C (78.3°F)
to 27.4°C(81.3°F), with wind speeds ranging from 7.6 to 27.7 kph (4.7 to 17.2 mph). Wind direction was
predominately out of the east-northeast.
MONITORING OF RELOCATED SEAGRASS
In May 2016, prior to wavebreak structure construction, seagrass patches within the structure footprint
and construction corridor were relocated to two planting areas on the south side of the construction
footprint.The percent cover of seagrass within each planting area and within the surrounding reference
area was evaluated immediately following relocation and during each monitoring survey.
In October 2018, at the time of the Year 2 Biannual Monitoring Survey, seagrasses were present within
both planted areas, but covers was relatively low at 14.9%, and dominated by H. wrightii(Table 22;
Photo 1). Average percent cover of total seagrass in reference areas was high at approximately 100%
(Table 2; Photo 2), where H. wrightii was also dominant.
From the initial survey in May 2016 (immediately following relocation) to the most recent survey in
October 2018, seagrass cover decreased by approximately 17.8%in the planted areas and increased in
the reference area by approximately 53.1% (Table 2). Sand scour from the wavebreak structure may be
impacting seagrasses in planted areas as sediment elevation was notably higher in the lee of the
structure, where planted areas are located, relative to other areas.The observed increase in the
reference area may be due to seasonality in seagrass growth, as the October survey occurred at the end
of growing season, and thus likely captured the higher cover that developed during summer months.
Cover is'specific cover'as quadrats are placed only within areas colonized by seagrass(as opposed to'areal cover'which
would include any unvegetated seafloor arising from random placement of quadrats)
2 The average BB scores were converted to percent cover for each area to allow interpolation of averaged BB scores that fall
between BB scale values(conversion was conducted by regressing the mid-point of percent cover associated within the range
covered by each BB scale value,on the associated BB scale value: Percent Cover=2.8108*[BB]z.23zs)
CSA Ocean Sciences Inc. 2 19 November 2018
CSA-NCDOT-FL-18-1830-2845-09-MEM-01-VER02

IN
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Photo 1. Representative image of in situ quadrat surveyed for percent cover in the planted areas.
Photo taken in the eastern planted area on 7 October 2018.
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Photo 2. Representative image of in situ quadrat surveyed for percent cover in the reference area.
Photo taken in the reference area on 7 October 2018.
CSA Ocean Sciences Inc. 3 19 November 2018
CSA-NCDOT-FL-18-1830-2845-09-MEM-01-VER02

Table 2. BB scores and associated percent cover* for seagrass within the planting and reference areas
for the Bonner Bridge Seagrass Mitigation Site.
Planting Area Reference Area
Survey
Total Seagrass BB Percent Cover Total Seagrass BB Percent Cover
May 2016 3.0 32.7 3.6 49.1
January 2017 0.3 0.2 1.5 7.0
October 2017 0.0 0.0 4.0 62.1
May 2018 0.55 0.7 3.3 40.4
October 2018 2.11 14.9 5.0 100
Change from May 2016 -0.89 -17.8 +1.4 +53.1
to October 2018
(*)specific cover
SEDIMENT ELEVATION
In May 2016, a center rod was installed in the middle of each of 40 seagrass patches across the study
area in addition to 4 rods installed in sandy substrate, for a total of 44 sediment elevation monitoring
stations. During the initial survey in May 2016, the average rod height within patches was 6.85 cm
(2.70 in.) above the sediment and 6.88 cm (2.71 in.) above the sediment within sandy substrate
(Table 3). In October 2018, a total of 31 of the original 40 center rods in seagrass patches were located,
with an average rod height of 16.27 cm (6.41 in.).Two of the four rods in sandy substrate were located
with an average rod height of 14.00 cm (5.51 in.). Missing rods were likely buried at the time of the
survey and were not located despite attempts to uncover them.
Since the Baseline Survey in January 2017, sediment depth across the Bonner Bridge Seagrass Mitigation
study area has decreased (increased rod height) within both the seagrass patches and sandy substrate
locations by 9.42 cm (3.71 in) and 7.12 cm (2.80 in), respectively(Table 4).
Table 3. Average rod height in centimeters above the sediment for the sediment elevation
monitoring.
Survey Rods in Center of Seagrass Patches(cm) Rods in Sandy Substrate(cm)
May 2016 6.85 6.88
January 2017 11.03 12.40
October 2017 16.55 12.00
May 2018 14.73 14.00
October 2018 16.27 14.00
Change from
May 2016 to +9.42 +7.12
October 2018
WAVE SENSORS
Wave sensors(RBRvirtuoso models) at the two long-term wave energy regime monitoring stations(one
each 25 m north and south of the structure) were retrieved, and data since the last monitoring event
(May 2018)were successfully downloaded; all data were present. One wave sensor was also utilized for
WEMo model validation via systematic relocation across the site to collect data from 24 stations both
north and south of the structure. WEMo computation for these stations and comparison of predicted
CSA Ocean Sciences Inc. 4 19 November 2018
CSA-NCDOT-FL-18-1830-2845-09-MEM-01-VER02

wave heights versus observed will follow in future reports and will be based on water depth and wind
conditions of the survey date versus observed wave heights from the mobile wave sensor.
EPIBIOTIC MONITORING STATIONS
Maintenance of the epibiotic monitoring stations on the structure was completed during the Year 2
Biannual Survey, which entailed the finding and cleaning of all 60 permanent monitoring tags and
re-etching of indentations on the concrete when possible to ensure the exact placement of the camera
framer during subsequent surveys. Barnacle and oyster growth prevented re-etching of the concrete on
the majority of stations in the middle and lower strata (Photo 3). Photographs of each epibiotic
monitoring station and subsequent quantitative percent cover analyses will be performed during all
annual surveys.
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Photo 3. Close-up photograph of barnacle and oyster growth on middle strata of the wavebreak
structure. Photo taken 7 October 2018.
If you have any questions concerning this report, please feel free to contact me at [phone] or
[e-mail].
Sincerely,
e.740.1"......_c
Erin Hodel
Senior Program Manager—Ports, Harbors, & Beaches
CSA Ocean Sciences Inc. 5 19 November 2018
CSA-NCDOT-FL-18-1830-2845-09-MEM-01-VER02

" IAA
C S A
CSA Ocean Sciences Inc.
SUMMARY OF YEAR 2 BIANNUAL SURVEY- OCTOBER 2018 - LETTER REPORT
DOCUMENT NO. CSA-NCDOT-FL-18-1830-2845-09-MEM-01-VER02
VERSION DATE DESCRIPTION PREPARED BY: REVIEWED BY: APPROVED BY:
01 11/19/2018 Initial draft for E. Hodel M. Fonseca E. Hodel
review
02 11/19/2018 Revised draft E. Hodel L.Ka bay E. Hodel
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current revision.Controlled copies are available
on the Management System network site or on request from the Document Production team.

. 67i a s
B-2500 Bonner Bridge Seagrass Mitigation Site
Year 2 Annual Survey Report
August 2018
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Prepared for: Prepared by:
Environmental Analysis Unit CSA Ocean Sciences Inc.
North Carolina Department of Transportation 8502 SW Kansas Avenue
Stuart, Florida 34997

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CSA Ocean Sciences Inc.
B-2500 Bonner Bridge Seagrass Mitigation Site
Baseline Monitoring Survey
DOCUMENT NO.CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN
Version Date Description Prepared by: Reviewed by: Approved by:
01 07/20/18 Initial draft for M.Fonseca J. Pennell M. Fonseca
review E.Hodel
M.Fonseca
02 07/31/18 Revised draft E.Hodel K. Metzger M. Fonseca
M.Fonseca
FIN 08/13/18 Final E.Hodel N/A M. Fonseca
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

Table of Contents
Page
List of Tables iv
List of Figures v
List of Photos vii
1.0 Introduction 1
2.0 Methods 2
Monitoring of Relocated Seagrass 3
Seagrass Cover 5
Sediment Elevation 6
Wave Regime and Model Validation 8
Epibiota Monitoring 14
3.0 Results 18
Monitoring of Relocated Seagrass 18
Seagrass Cover 22
Sediment Elevation 25
Wave Regime and Model Validation 37
Epibiota Monitoring 41
4.0 Conclusions 46
5.0 References 48
Appendices 50
Appendix I Project Site Selection I-1
Appendix II Bioturbation Experiment II-1
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN iii

List of Tables
Table Page
1 Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation
Site 2
2 Braun-Blanquet scale (score) and percent cover scale values (Braun-Blanquet, 1972) 5
3 BB scores and associated percent cover for seagrass within the planting and
reference areas for the Bonner Bridge Seagrass Mitigation Site by survey 19
4 One-way ANOVA testing differences in sediment elevation (ft, MLLW)from rods
installed at previous bioturbation patches among all combinations of surveys 27
5 Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey 28
6 Areas for the wave energy reduction zones depicted in Appendix I in both acres and
square meters 37
7 Percent cover of biota and concrete from concrete monitoring stations during the
Baseline Monitoring Survey in January 2017 and the Year 1 Annual Monitoring
Survey in May 2018 45
8 Percent cover of biota and rock from rock monitoring stations during the Baseline
Monitoring Survey in January 2017 and the Year 1 Annual Monitoring Survey in
May 2018 45
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN iv

List of Figures
Figure Page
1 Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site,
showing the position of the seagrass planting areas,the construction corridor and
the structure itself 4
2 Schematic (not to scale) layout of the near field (to wavebreak) sediment elevation
transects 9
3 Sand apron south of wall visually outlined 10
4 Stationary and temporary locations of the pressure sensors at the Bonner Bridge
Seagrass Mitigation Site 11
5 Epibiota monitoring stations on the wavebreak at the Bonner Bridge Seagrass
Mitigation Site 16
6 Baseline classification results identifying areas of seagrass (yellow)within the
Bonner Bridge Seagrass Mitigation Site for the March 24, 2017 overflight 23
7 Enlarged view of baseline aerial imagery(left) and classification results(right)
identifying areas of seagrass (yellow)within the Bonner Bridge Seagrass Mitigation
Site for the April 18, 2018 overflight 24
8 Change in sediment elevation (ft, MLLW)over time monitored at rods installed in
previous bioturbation study 26
9 Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital
elevation model at the Bonner Bridge Seagrass Mitigation Site prior to construction
of the wavebreak(ultimate location of wavebreak shown) 27
10a Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 29
10b Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 30
10c Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 31
10d Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 32
10e Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 33
10f Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 34
10g Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 35
10h Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time 36
11 Hourly significant wave heights (m) measured at the wavebreak from January
through July 2017 for(a)Top- north side of the wavebreak and (b) Bottom -south
side of the wavebreak 38
12 Hourly significant wave heights (m) measured at the wavebreak structure from
January through May 2018 for(a) Top- north side of the wavebreak and
(b) Bottom -south side of the wavebreak 39
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN v

,
List of Figures
(Continued)
Figure Page
13 Difference in hourly significant wave heights(m) measured at the wavebreak
structure for(a)Top -Jannuary through July 2017 and (b) Bottom -January through
May 2018 40
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN vi

List of Photos
Photo Page
1 Aerial image of Bonner Bridge 1
2 Inverted "T" shape ruler used to measure rod height above or below the substrate
at the Bonner Bridge Seagrass Mitigation Site 7
3 Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner
Bridge Seagrass Mitigation Site 7
4 Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site 12
5 Re-engineered wave sensor bracket installed in January 2018 to hold the sensor
vertical and further away from the sand surface 13
6 Numbered tag installed at every monitoring station on the wavebreak at the Bonner
Bridge Seagrass Mitigation Site 17
7 PVC camera mount framer used to photograph every monitoring station on the
wavebreak at the Bonner Bridge Seagrass Mitigation Site 17
8 Transplanted seagrass with clean blades appearing similar to surrounding natural
seagrass at the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey 19
9 Natural seagrass in the reference area showing blades covered with a layer of
epiphytes at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey 20
10 Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site
during the October 2017 survey 20
11 Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site
during the May 2018 survey 21
12 Representative photo of rock substrate for a high elevation monitoring station
(Station 35) showing wet rock on the structure at the Bonner Bridge Seagrass
Mitigation Site during the May 2018 survey 42
13 Representative photo of concrete substrate for a high elevation monitoring station
(Station 35) showing wet concrete on the structure at the Bonner Bridge Seagrass
Mitigation Site during the May 2018 survey 42
14 Representative photo of rock substrate for a middle elevation monitoring station
(Station 28) showing wet rock, algae, and barnacle growth on the structure at the
Bonner Bridge Seagrass Mitigation Site during the May 2018 survey 43
15 Representative photo of concrete substrate for a middle elevation monitoring
station (Station 28) showing wet concrete, algae, and barnacle growth on the
structure at the Bonner Bridge Seagrass Mitigation Site during the May 2018 survey 43
16 Representative photo mosaic of rock substrate for a low elevation monitoring
station (Station 1) showing submerged rock and barnacle growth on the structure at
the Bonner Bridge Seagrass Mitigation Site during the January 2017 survey 44
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN vii

List of Photos
(Continued)
Photo Page
17 Representative photo mosaic of concrete substrate for a low elevation monitoring
station (Station 1) showing submerged concrete and barnacle growth on the
structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey 44
18 North-oriented view of the wavebreak installed in January 2017 at the Bonner
Bridge Seagrass Mitigation Site 47
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN viii

1.0 Introduction
The North Carolina Department of Transportation (NCDOT) contracted CSA Ocean Sciences Inc. (CSA) in
2012 (Contract No. 6300032017)to conduct in-kind seagrass (mixed Halodule wrightii, Ruppia maritima,
Zostera marina) mitigation of 1.28 acres (0.52 hectares)to compensate for losses anticipated to occur
during the replacement of the Herbert C. Bonner Bridge over Oregon Inlet, North Carolina (Photo 1). The
Bonner Bridge provides the only highway connection for Hatteras Island to the mainland in Dare County,
North Carolina and its replacement is currently under construction. Based on previous published
research in North Carolina (Fonseca et al., 1998, Fonseca et al., 2000, Kelly et al., 2001, Fonseca et al.,
2002) CSA conceptualized creating a wavebreak to modify existing, patchy seagrass habitat by
attenuating wave activity to promote more continuous, persistent seagrass coverage.This subsequent
increase in seagrass acreage was expected to meet NCDOT's seagrass mitigation requirements while
enhancing ecosystem services for the area.
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Photo 1. Aerial image of Bonner Bridge.
Source: http://www.kdhnc.com/667/Herbert-C-Bonner-Bridge-Replacement-Project
CSA Ocean Sciences Inc. (CSA) conducted the first Biannual Monitoring Survey (Year 1)for the Bonner
Bridge Seagrass Mitigation Site from 2 to 4 October 2017.The Year 1 Biannual Monitoring Survey was
initially scheduled for August 2017; however, due to tropical storm and hurricane activity and
subsequent above-average water depths in Pamlico Sound at the site, the survey was not conducted
until early October 2017. In 2018,the spring survey(May—June) was conducted from 13 to 17 May and
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 1

provides the data needed to submit this Year 2 Annual Survey Report. Table 1 describes CSA's previous
activities and future scheduled surveys.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wave break structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and May 2016 Complete
Bioturbation Experiment Initiation
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Installation 18 November 2016 to Complete
18 January 2017
Post-construction
Baseline Monitoring Survey 14 to 18 Jan.2017 Complete
Biannual Monitoring Survey 2 to 4 Oct.2017 Complete
Biannual Monitoring Surveys May and September 2018 Scheduled
Biannual Monitoring Surveys May and September 2019 Scheduled
Annual Monitoring Survey July 2020 Scheduled
Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.
2.0 Methods
The Year 1 Baseline and Biannual Survey Reports included:
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Monitoring of selected bioturbation experiment stations and removal of mesh when found;
• Collection of sediment elevation data;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation; and
• Maintenance of epibiota monitoring stations on the wavebreak structure.
This May 2018 Biannual Monitoring Survey includes:
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Collection of sediment elevation data
o Seagrass patch elevation rods
o SEPI near-field wavebreak surveys
• Download of long-term wave data and maintenance of wave sensors;
• Reporting of wave sensor data throughout the site over this and the past three surveys for WEMo
validation; and
• Monitoring of epibiota monitoring stations on the wavebreak structure
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina; September 2015) referenced in the
permit (Permit Modification No. 106-12) to ensure all monitoring requirements were met.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 2

During the October 2017 survey,scientists observed patchy seagrass habitat consisting of three species
of seagrass (Zostera marina, Halodule wrightii, and Ruppia maritima). Halodule wrightii was the most
prevalent species, followed by Z. marina and then R. maritima. The major substrate type observed
throughout the site was fine sand. Limited vessel traffic was observed during on-site surveys within the
immediate vicinity. Site conditions were relatively consistent during the survey, with slight variations
due to direction and strength of the wind. Average daily water temperatures during the survey ranged
from 22°C (72°F)to 23°C (73°F), with wind speeds ranging from 26.5 to 31.3 kph (16.4 to 19.5 mph).
Wind direction was predominately out of the north.
In May 2018, scientists observed patchy seagrass habitat consisting of three species of seagrass
(Zostera marina, Halodule wrightii, and Ruppia maritima). Halodule wrightii and Z. marina were both
commonly observed while R. maritima was rarely observed.The major substrate type observed
throughout the site was fine siliceous sand. Limited vessel traffic was observed during on-site surveys
within the immediate vicinity. Site conditions were relatively consistent during the survey, with slight
variations due to direction and strength of the wind. Average daily water temperatures during the
survey ranged from 23.4°C(74.2°F)to 24.8°C (76.7°F), with wind speeds ranging from 7.6 to 41.1 kph
(4.7 to 25.5 mph). Wind direction was predominately south-southwest.
Sections of this report that refer to construction and engineering activities or permits where originally
developed using English units, will follow the convention of reporting first in English units and then
parenthetically in metric units. For the sections of the report not directly associated with structural
engineering, the convention of reporting will be metric units followed by English units parenthetically.
Sections of the early reports describing initial project activities have now been moved to Appendices in
order to focus on long-term post-construction monitoring. Project Site Selection and Project Engineering
and Design sections were initially described here in previous reports.This historical material has now
been moved to Appendix I.Additionally,the description of an attempted experiment to assess the
relative contribution of bioturbation to patch maintenance (versus wave energy) has been moved to
Appendix II.
MONITORING OF RELOCATED SEAGRASS
In 2016, prior to installation of the wavebreak structure, the State of North Carolina Department of
Environmental Quality and Coastal Resources Commission permit (Permit Modification No. 106-12)
required any seagrass within the structure footprint and the construction corridor to be moved to the
lee side of the structure onsite. In May 2016, seagrass patches within the structure footprint and
construction corridor were relocated to two planting areas on the south side of the construction
footprint (Figure 1).
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 3

zz75'351 5"W 75'35'14'W 75°35'13'W 75°3517W 75°35'11"W 75'35'10'W 75'35'9"W 75'35'8". 75°35'7'W
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Figure 1. Aerial image of the wavebreak area at the Bonner Bridge Seagrass Mitigation Site, showing the position of the seagrass planting
areas, the construction corridor and the structure itself. Examples of randomly selected seagrass survey points are shown for
surveys within the planted areas and nearby reference locations.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 4

Percent cover of seagrass within relocation areas was evaluated immediately after transplanting. Each
time, scientists navigated to 10 pre-selected locations (proportionally assigned to seven locations in the
larger eastern relocation area and three in the smaller western relocation area) within the planting
areas using the Trimble Geo XH GeoExplorer 2008 Series GPS.
To compare the colonization of the planted areas to the surrounding natural areas,five additional
random locations were selected in the surrounding natural areas (reference area) within a 50-meter
(164-foot) distance of the planting areas (Figure 1). At each location, a 1-m2 (11-ft2) quadrat was
centered over each point and percent cover of seagrass was assessed using a modified Braun-Blanquet
(BB) cover and abundance technique (Braun-Blanquet, 1972; Kenworthy and Schwarzchild, 1997;
Fourqurean et al., 2001). Within the quadrat a BB scale value (Table 2) was independently evaluated for
percent cover of each seagrass species as well as total seagrass.Average BB scores were then converted
to percent cover for each area to allow interpolation of averaged BB scores that fall between BB scale
values (conversion is conducted by regressing the mid-point of percent cover associated within the
range covered by each BB scale value, on the associated BB scale value: Percent Cover=
2.8108*[BB]2.2325).
Table 2. Braun-Blanquet scale (score) and percent cover scale values (Braun-Blanquet, 1972).
Braun-Blanquet Scale(Score) Percent Cover(%)
0.0 Not present
0.1 Solitary specimen
0.5 Few with small cover
1 Numerous, but<5
2 5 to 25
3 25 to 50
4 50 to 75
5 75 to 100
Seagrass Cover
Seagrass cover was determined by classifying areas of seagrass occurring within the Bonner Bridge
Seagrass Mitigation Site based on aerial imagery. A georeferenced, high-resolution mosaicked aerial
image (collected by NCDOT on 18 April 2018)was used for the first classification of seagrass areas. The
aerial image was color-infrared (CIR)with a resolution of 0.08 m (0.25 ft).The image was subdivided into
separate classification areas of interest (A01) based on similar pixel spectral signature ranges. Separate
classification of each AOI helped to eliminate variations in reflectance and environmental conditions
across the entire project area in order to reduce classification confusion. An unsupervised classification
was then performed on each classification AOI using a combination of iso cluster and maximum
likelihood techniques using ESRI ArcGIS 10.4 software.After running the unsupervised classifications,
each A01 was manually interpreted by denoting visually apparent classes of seagrass and classes of
non-seagrass. Spectral noise and holes within the classification results were removed and corrected
using a combination of majority filter, region group, set null (enhanced boundary edges and removed
groups of small non-contiguous pixels that were smaller than a specified value), and eliminate polygon
part (eliminated areas that were less than a specified value) tools in ArcGIS. Lastly, a manual
classification technique was then applied to the classification with guidance from a GIS analyst.This
consisted of removing areas of over-classification and adding-in (digitizing) areas where
under-classification occurred, again based on visually apparent seagrass cover.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 5

Sediment Elevation
Sediment elevation is being documented with three methods: (1) measurements of sediment height
relative to 2 m long rods installed to near the sediment surface in seagrass patches used for the previous
bioturbation studies, (2) a broad-scale digital elevation model created using an RTK-equipped (realtime
kinematic) unmanned surface vehicle (USV) and (3) near-field transect surveys around the wavebreak.
Rod Heights: This method utilized during all monitoring surveys was by direct measurement of the
height of the center rod above the sediment at each of the 40 stations originally established for the
bioturbation experiment (see Appendix II). At each station,the rod height above the sediment was
measured using a meter stick fastened to a piece of wood (24 cm x 5 cm x 5 cm [18 in x 2 in x 2 in]).The
0-mark on the meter stick was attached to the center of the wood piece creating an inverted "T" shape
(Photo 2).The wood was laid flush against the seafloor to provide more surface area to avoid the ruler
sinking into the substrate.The meter stick was placed next to the rod to obtain the measurement of the
rod height above the substrate. In addition to the 40 center rods, four additional sediment rods (one per
wave energy regime) were installed in sandy substrate and rod height above the substrate was
measured for each.
This monitoring is continuing and update results are provided in this report. Change in sediment
elevation among surveys and across the wave energy strata was computed for each combination of
survey times (survey 1 vs 2, 1 vs 3, 1 vs 4, 2 vs 3, 2 vs 4 and 3 vs 4).The differences in change in sediment
elevation among strata for each comparison of survey times were compared in a 1-way ANOVA using
PROC GLM in SAS 9.2 after In + 10 transformation (to avoid negative numbers and address any
non-normality of the data.
USV Digital Elevation Model: A second method was employed to evaluate the entire area forecast to be
affected by the wavebreak. In June 2016, CSA used an Unmanned Surface Vehicle (USV) to develop a
sediment digital elevation model to document changes in shoal elevation associated with the wavebreak
installation.The USV(Photo 3) was pre-programmed to run a pre-selected geographic grid at 50-m
(164-ft) spacing which encompassed the entire site. Bathymetry data was collected using duel
frequency, single beam sonar at a rate of 220 to 224 kHz.A Trimble RTK system (RTK)was mounted on
the USV to integrate real time navigation while the USV ran the pre-programmed grid lines (speed of
approximately 9 kph [5.7 mph]).The RTK had a horizontal and vertical accuracy of 2 cm (±0.787 in) and
real-time tidal corrections were applied to accurately determine water levels across the site.This survey
will be repeated at the end of the five-year monitoring period in 2021.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 6

--.17.'•-'.., .-...r.i. ,....,"••• , ,„,- «, .7 . .-
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Photo 2. Inverted "T" shape ruler used to measure rod height above or below the substrate at the
Bonner Bridge Seagrass Mitigation Site.
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Photo 3. Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner Bridge
Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 7

Near-field Wall Sediment Elevation Survey: Starting in June 2017 a third method of sediment elevation
assessment was initiated. SEPI Engineering Inc. (SEPI)was contracted by NCDOT to conduct high density,
near-field sediment elevation measures in the vicinity of the wavebreak structure. North-south oriented
transects were established at five equally spaced locations centered on the wavebreak (Figure 2) and
sediment elevations corrected to MLLW surveyed (June 2017, September 2017 and then monthly
starting January 2018; reported here through June of 2018).Transects were placed on both the north
and south side of the wavebreak. In 2017, elevations at distances of 0 (at the edge of the wavebreak
structure), 5, 10, 20, 50, 75, and 100 ft were recorded. In January of 2018 that changed to increments of
5 feet out to a distance of 50 ft and then at 75 and 100 ft to improve sensitivity of detecting any
systematic change in sediment elevation. Starting in June of 2018, distances of 125 and 150 ft were
added to ensure elevation samples were taken beyond the apparent apron of recently moved sand seen
in aerial images(Figure 3).These data have been provided to CSA and analyzed in this report. Elevations
were compared in a 2-way ANOVA using PROC GLM in SAS 9.2 after In + 10 transformation (to avoid
negative numbers and address any non-normality of the data). Main effects were distance from the wall
and side of the wall,tested at individual dates along with assessment for interaction of main effects.
Wave Regime and Model Validation
Long Term Wave Regime: Long-term wave energy regime monitoring stations were placed at the
Bonner Bridge Seagrass Mitigation Site in "Month Year" using pressure sensor loggers to record wave
characteristics. Starting in January 2017 two pressure sensors (RBRvirtuoso models) were deployed at
stationary locations 25 m (82 ft) in front(north) of and behind (south)the wavebreak (Figure 4).
Pressure sensors were cylindrical and approximately 5 cm (2 in) in diameter by 25 cm (10 in) long and
were mounted in a locked casing horizontally on the seafloor approximately 15 cm (6 in) above the
substrate on a solid base, concrete-filled pillar set 0.91 m (3 ft) into the seafloor(Photo 4). Pressure
sensors were set to record bursts of pressure data every 30 minutes at a sampling rate of 4 Hz for
128 seconds.These data also provide water level and tide documentation specifically for the site in
order to evaluate the wave energy regime impinging on the north and south faces of the wavebreak
structure.
In November of 2017 the sensors were removed and sent back to the manufacturer for calibration and
assessment of impacts from sand impaction and biofouling that had occurred around the wave sensor
port. This servicing caused the sensors to be out of service until their re-deployment on 16 January
2018. Communication with the RBR technical representatives indicated that the sediment impaction and
biofouling did not affect the detection of wave characteristics. Nonetheless, upon redeployment,the
sensor brackets were revised to hold the sensors in a vertical posture and with the wave sensor window
down-facing(Photo 5) in order to minimize sand collection in the sensor port through gravity. The
sensors were re-deployed in January 2018 and have been recording continuously since that time. Data
were harvested in May 2018 and both the January—July 2017 and the January—May 2018 data are
reported here.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 8

Bonner wavebreak sediment elevation transect layout
15 sediment elevations pertransectat0,5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 125, 150 feet
15 sediment elevation locationspertransect
Notto scale
Wavebreak
Pile 51
Pile 76
Pile 25
♦
Pile 101
Pile 1
All transects at a right angle to th is red dashed baseline
Figure 2. Schematic (not to scale) layout of the near field (to wavebreak) sediment elevation transects.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 9

r
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Figure 3. Sand apron south of wall visually outlined.
CSA-NCDOT-FL-18-1830-1845-09-REP-01-FIN 10 .

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Figure 4. Stationary and temporary locations of the pressure sensors at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 1

NO �
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Photo 4. Photograph of one of the two wave sensor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site. The hinged bracket is shown being
lifted; a disposable padlock is installed through the hinged piece to keep the sensor secure.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 12

qT
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Photo 5. Re-engineered wave sensor bracket installed in January 2018 to hold the sensor vertical and
further away from the sand surface.
WEMo model validation:This is being developed through opportunistic sampling. During times of onsite
monitoring surveys, an RBR sensor was systematically but temporarily relocated across the site
(Figure 4)to obtain a spatial assessment of predicted (WEMo computation to follow based on water
depth and wind conditions of the survey date)versus observed wave heights from the mobile sensor.
This spatial assessment was performed on May 18, 2016,January 15, 2017, October 4, 2017 and May 15,
2018 to provide a geographically articulated assessment of wave energy distribution with regard to
prevailing conditions.The relocated pressure sensor was set to record bursts of pressure data at a
sampling rate of 4 Hz for 128 seconds during this sampling. During these surveys one of the long-term
RBR sensors was used. During each survey, a scientist recorded the wind speed using hand-held
anemometers as well as wind direction prior to sampling and again after sampling was complete. Wave
data from pressure sensors were downloaded into Ruskin software (V1.13.7) and exported to Microsoft
Excel for analysis. Analysis is ongoing and will be comprised of simple univariate statistics of wind speed
but also predicted versus observed regression to determine the likely on-site accuracy of the
WEMo-derived wave forecasts.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 13

Epibiota Monitoring
Epibiota monitoring on the wavebreak was initiated in January 2017 through the establishment of
randomly-placed, permanent monitoring stations (Figure 5). Digital photographs were recorded at each
station as a time-zero (uncolonized) baseline against which subsequent epibiota colonization will be
compared for each survey time. Stations were stratified by the sides of the wavebreak(30 on the
exposed side [north] and 30 on the sheltered [south] side) at different vertical elevations related to the
individual wave attenuator unit placement (high, middle, and low).Ten replicate stations were randomly
assigned per elevation on either side of the wavebreak for a total of 60 monitoring stations. Random
locations were selected along the wavebreak and a vertical elevation was randomly assigned to each
location. Scientists used the Trimble GPS to navigate to the pre-selected random monitoring
station/elevation replicate along the wavebreak. Monitoring stations were separated by a minimum of
one Reefmaker unit. The exact horizontal location of the monitoring station on a wave attenuator unit
was visually determined where rock placement was closest to the edge of the concrete, making them
easier to photograph. Some wave attenuator units had smaller rock embedded in the concrete, so often
two small rocks were selected for monitoring.To identify the precise monitoring location and allow
precise alignment for subsequent photographs, a numbered tag was installed on the rock immediately
to the right of the selected rock(s)to be monitored (Photo 6) and alignment points marked on the
concrete surface.
A Sony A5000 digital camera in an underwater housing was installed on a PVC camera mount framer to
photograph the concrete and rock(s) at each monitoring station.The PVC frame (Photo 7) was included
in every photo to ensure standardization of photo size (dimension of the frame was 20.3 cm x 30.5 cm
[8 in x 12 in]).The camera housing was fixed to the framer with a distance of 25.7 cm (10 in)from the
housing lens to the outer edge of the frame.
To photograph the concrete portion of the wave attenuator units, the entire framer was placed flush
with the side of the concrete so the bottom edge of the concrete was included within the frame.To
photograph the rock(s), the bottom of the framer was placed flush with the top edge of the concrete
layer(where the selected rock was embedded) and the top of the framer rested on the concrete layer
located above the selected rock(s) (approximately 15° angle).
During the May 2018 survey,the low elevation strata monitoring stations were entirely submerged
during all observed tidal stages.This, coupled with high turbidity levels, reduced visibility to less than
one foot.As a result,the method used to photograph the low elevation stations was slightly modified.
The camera was removed from the framer to allow capture of close-up photos within visibility limits.
The framer was still held against the concrete as described previously,yet due to the decreased distance
between the camera and the rock or concrete, multiple photographs were collected to image the entire
area within the framer (typically four photos).The multiple photographs were then stitched together
using Adobe® Photoshop®to create a single photograph of each low strata rock or concrete monitoring
station.
One photo of the concrete and one photo of the rock(s)were collected for all 60 monitoring stations,
resulting in 120 digital images. Digital images were processed and analyzed using Coral Point Count with
Microsoft Excel extensions(CPCe)V4.1 software analysis program (Kohler and Gill, 2006). CPCe utilizes
the random point count method described by Bohnsack(1979)to accurately estimate percent cover of
benthic organisms and substrate from digital images. Because the rocks were all different sizes, it was
necessary to assign a number of random points that was proportional to the size of the rock (i.e., a
larger rock would have a greater number of random points assigned). The total area of evaluated rock
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 14

was calculated for each image using the measurement tool in CPCe. For purposes of this assessment,we
assumed that all rocks were equidistant from the camera lens. From these calculations, average rock
size was determined to be 112.4 cm'and was assigned 10 random points.The number of random points
assigned to each image was then increased or decreased proportionally to the size of the rock(s); the
number of random points for rock images ranged from four to 22. Because the area of concrete
assessed was the same in each photo, all concrete images were assigned the same number of random
points (41), and points were restricted to the area of the photograph containing concrete. Random
points were projected on each image, and the biota or substrate located beneath each point was
identified to the lowest possible taxonomic level (for the time-zero images, no biota were detected).
Data from each image were assembled in a spreadsheet for percent cover calculations and subsequent
comparative analysis.
C5A-NCDOT-FL-18-1830-2845-09-REP-01-FIN 15

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Figure 5. Epibiota monitoring stations on the wavebreak at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 16

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Seagrass Mitigation Site.
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Photo 7. PVC camera mount framer used to photograph every monitoring station on the wavebreak at
the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 17

3.0 Results
During visits to the site, scientists observed that the Bonner Bridge Seagrass Mitigation Site was
composed of patchy seagrass habitat consisting of multiple species including Zostera marina,
Halodule wrightii, and Ruppia maritima. Very fine sand (visual observation) sediments were the
dominant substrate type observed. Limited vessel traffic was observed during onsite surveys within the
immediate vicinity although commercial crabbing vessels were observed crossing the general shoal area.
Site conditions varied during each survey and were largely driven by direction and strength of the wind.
Strong northeasterly winds on site resulted in lowered water level at the site and strong southwesterly
winds resulted in higher water levels. Weather conditions during the surveys ranged from a high
temperature of 75°F (May 2016)to a low temperature of 39°F (January 2017)with wind speeds ranging
from 8 to 48 kph (5-30 mph)from various directions.
MONITORING OF RELOCATED SEAGRASS
Prior to construction, seagrass patches within the structure footprint and construction corridor were
relocated to two planting areas on the lee side of the wavebreak structure (Figure 1). In May 2016,
immediately after relocation,the percent cover of seagrass was evaluated within the relocation areas
and within the surrounding reference area. Upon completion of relocation, percent cover of seagrass
was 32.7%for the relocation areas and 49.1%for the reference area (BB scores of 3.0 and 3.6,
respectively).Transplanted seagrass within the relocation areas appeared similar to the surrounding
natural seagrass and the borders of the planting areas were visibly indistinguishable (Photo 8). All
seagrass blades were bright green and visibly clear of epiphytic growth.
In January 2017, immediately following construction of the wavebreak structure, the percent cover of
seagrass within the planting areas was evaluated again.The planting areas had a percent cover of
0.2% and the natural reference areas had a percent cover of 7% (BB scores of 0.2 and 1.5, respectively)
(Table 3). In January 2017, a brown epiphytic layer covered the majority of the visible seagrass blades
and small tufts of brown macroalgae were observed colonizing the substrate often mixed in with
seagrass (Photo 9). Seagrass cover declined by 32.5% in the planting areas and 42.1% in the reference
areas, indicating a substantial overall drop in coverage.
In October 2017, no seagrass was observed in the planted areas. Cover in the reference areas was
approximately 62%, well above the baseline cover of 49%observed in May 2016 (Photo 10). Seasonality
in seagrass growth may be responsible for the higher cover observed in October, with higher cover
expected at the end of growing season in October versus the beginning of growing season in May.
During the most recent survey in May 2018, sparse seagrass was observed in the planted areas, but
cover was still <1%, marking a decrease of approximately 32%since the initial survey in May 2016. Cover
in the reference area was approximately 40%, similar to the cover observed in May 2016 (Photo 11).
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 18

Table 3. BB scores and associated percent cover for seagrass within the planting and reference areas
for the Bonner Bridge Seagrass Mitigation Site by survey.
Planting Area Reference Area
Survey
Total Seagrass BB Percent Cover Total Seagrass BB Percent Cover
May 2016 3.0 32.7 3.6 49.1
January 2017 0.3 0.2 1.5 7.0
October 2017 0.0 0.0 4.0 62.1
May 2018 0.55 0.7 3.3 40.4
Change from May -2.45 -32.0 -0.3 -8.7
2016
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Photo 8. Transplanted seagrass with clean blades appearing similar to surrounding natural seagrass at
the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 19

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Photo 9. Natural seagrass in the reference area showing blades covered with a layer of epiphytes at
the Bonner Bridge Seagrass Mitigation Site during the January 2017 survey.
Photo 10. Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site during
the October 2017 survey.
CSA-NCDOT-FL-18-1830-2845-09-REP-0I-FIN 20

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Photo 11. Natural seagrass in the reference area at the Bonner Bridge Seagrass Mitigation Site during
the May 2018 survey.
Several factors may have contributed to the loss of seagrass within the planted areas that was initially
observed in January 2017. Seagrass was relocated to gaps within natural seagrass patches in May 2016
prior to installation of the wavebreak structure. Construction was originally scheduled for June 2016 but
delayed until November 2016 and completed in January 2017. Previous studies have shown if seagrass is
relocated to areas naturally devoid of seagrass without modifying the existing environment, natural
processes will continue to preside and the relocated seagrass should not necessarily persist
(Fonseca et al., 1998). Additionally, Hurricane Matthew passed through the Pamlico Sound and
surrounding areas on 8 and 9 October 2016, five months after seagrass relocation, prior to the
installation of the wavebreak structure. The hurricane had average wind speeds ranging from 32 to
64 kph (20 to 40 mph) with maximum wind speeds of 129 kph (80 mph) initially from the north, and
then switching direction out of the southeast as the storm passed. Severe flooding occurred along the
coast with an average rainfall of 22.1 cm (8.7 in) (http://www.weather.gov/mhx/MatthewSummarv). It
is possible that the relocated seagrass had not fully established a sufficiently robust root and rhizome
system during the five months from relocation to the storm event, leaving them susceptible to erosion.
Additionally, sand accumulation on the south side of the structure due to scouring has been observed in
physical monitoring surveys and may be inhibiting seagrass survival in the immediately adjacent planted
areas.
Seagrass cover in coastal North Carolina naturally declines in winter months (Thayer et al. 1984) and
therefore lower cover was expected during the January 2017 survey. Cover in the reference area was
also very low at this time (7%),which also may have been attributable to Hurricane Matthew and/or the
sampling event occurring in winter. Since the January 2017 survey, seagrass in the planted areas has not
recovered and cover remains<1%. However, seagrass in the reference area has recovered and percent
cover is similar to that observed during the initial survey in May 2016.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 21

Seagrass Cover
The Bonner Bridge Seagrass Mitigation Site was forecast to include 301.6 acres (122.1 hectares), and
boundaries were determined by using the wave forecast model prediction. Seagrass cover within these
boundaries was determined by classifying areas of seagrass based on aerial imagery provided by NCDOT.
Classification resulted in 24.9 acres (10.1 hectares (versus 33.4 acres [13.5 hectares] in 2017) of seagrass
cover over the 301.6 acre (122.1 hectare) site (Figures 6 [2017] and 7 [2018]). By visual estimation it
appears that seagrass cover was lost in the patchy areas north and east of the wavebreak.
In aquatic systems, classification methods rarely achieve 100%accuracy.This is because, unlike
terrestrial systems,whose classification is limited primarily by atmospheric conditions, classification of
aquatic systems, especially benthic components, is limited by both atmospheric and water conditions.
Thus, the accuracy of seagrass classification largely depends on water clarity and sea surface condition
at the time of imagery acquisition. Weather events have an effect on waves on the water surface which
actively degrade visualization of the seafloor, as well as water clarity. In addition, wind events occurring
immediately prior to imagery collection may cause latent sediment suspension that negatively impact
results. Finally, many seagrass patches were interdigitated with sand and often non-contiguous, which
complicates precise delineation. In addition to atmospheric and water column effects, mosaicking of the
image produced shading gradients which interfered with seagrass classification accuracy of the seagrass
areas and appeared to be the source of most inaccuracy. An absence of ground control points taken in
association with the imagery impeded further accuracy assessment. In both 2017 and 2018,
interpretation of seagrass cover was compromised by the generally poor quality of the imagery. Large
areas of high surface reflectance and presence of white`flecks' in the imagery over much of the AOI
impaired or completely prevented interpretation of seagrass cover. Discrimination of seagrass cover
apart from sand was also made difficult because of low contrast among the two habitat types.This may
have resulted from high water levels, high visibility, low sun intensity or some combination thereof.
Upcoming utilization of low-altitude, high resolution imagery should improve seagrass cover delineation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 22

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Figure 6. Baseline classification results identifying areas of seagrass (yellow) within the Bonner
Bridge Seagrass Mitigation Site for the March 24, 2017 overflight.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 23

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Figure 7. Enlarged view of baseline aerial imagery (left) and classification results(right) identifying
areas of seagrass (yellow)within the Bonner Bridge Seagrass Mitigation Site for the
April 18, 2018 overflight.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 24

Sediment Elevation
Rod Heights: Sediment elevation was monitored across the entire site by measuring the center rods at
40 seagrass patches selected for a bioturbation study(see Appendix II for description of this
since-terminated experiment) and four additional sediment rods placed in sandy substrate.These
40 rods were installed in May 2016 at locations randomly selected from within strata (10 per strata)
defined by the forecasted wave reduction pattern following wavebreak placement (high wave energy
reduction = >66%; moderate reduction = 34 to 66%, low reduction =5 to 33%, and ambient or reference
=<5% reduction (Appendix Figure II-1). Across all surveys, no rods were located that were below the
sediment surface despite extensive searching and probing. If buried rods were not located, this would
suggest that the surveys were potentially biased towards measurements indicating a lower elevation of
the sediment surface.
The average rod height above the sediment in May 2016 was 6.8 cm (2.7 in).The average height of the
four sediment rods above the sediment was 6.9 cm (2.7 in). In January 2017, a total of 32 center rods
were relocated and the average rod height was 11.0 cm (4.3 in).Two of the four sediment rods were
relocated and the average rod height was 12.4 cm (4.9 in). The eight center rods not located may be
deeply buried and future attempts will be made to locate them. If they were deeply buried then the
average rod height would decrease.
In October 2017, sediment elevation was monitored at the center rod of the 14 patches monitored for
bioturbation in addition to the original 4 rods in sandy substrate.The center rod was not located (likely
due to burial) at 3 of the 14 seagrass patch locations and 1 sandy substrate location.The average height
of center rods in seagrass patches was 16.5 cm (6.5 in.) and 12.0 cm (4.7 in.) at sandy substrate stations.
Sediment depth had decreased (increased rod height)within seagrass patches and remained similar at
the sandy substrate locations since the Baseline Survey in January 2017.
In May 2018, sediment elevation was again monitored at the center rod of the 14 patches monitored for
bioturbation, in addition to the original 4 rods in sandy substrate.The center rod was not located (likely
due to burial) at 3 of the 14 seagrass patch locations and 1 sandy substrate location.The average height
of center rods in seagrass patches was 14.7 cm (5.8 in.) and 14.0 cm (5.5 in.) at sandy substrate stations.
Sediment depth has decreased (increased rod height) within seagrass patches and remained similar at
the sandy substrate locations since the Baseline Survey in January 2017.
Change in sediment elevation was computed among the replicate rods in each of the wave energy
reduction strata among all combinations of survey dates (Figure 8).There was considerable variation in
the change in sediment elevation among wave energy strata over time. A one-way ANOVA revealed that
only comparisons in sediment elevation among surveys 1 and 4 and surveys 2 and 4 showed some
significant differences among strata (Table 4). In those two instances the area of low wave energy
reduction (furthest from the wall and abutting the reference strata) had the greatest change (loss) in
elevation. No clear pattern of sediment accumulation across wave energy strata emerges from this
analysis.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 25

Change in sediment elevation (ft MLLW) by wave reduction zone
A Survey 1 4 2 A Survey 1-4 3 A Survey 1 4 4 A Survey 2-i 3 A Survey 2 4 4 A Survey 3 4 4
0.5 iti 0.5- 0.5- 0.5- _ 0.5- 0.5-
0.4 0.4- 0.4- 0.4- 0.4- 0.4-0.3 0.3- 0.3- 0.3- - 0.3- 0.3- -
0.2 0.2- - _ _ _
0.2- 0.2- 0.2- - - 0.2-
0.1 0.1- 0.1- - 0.1- 0.1- 0.1-
0.0 0.0- - - 0.0-- - 0.0- 0.0 0.0-��
-0.1 -0.1- • -0.1- _0, -0.1- _ -0.1- -
-0.2 -0.2- -0.2- - -0.2- -0.2 -0.2-
-0. -0.3- -0.3- -0.3 -0.3• -0.3-
-0. -0.4- -0.4 -0.4- -0.4- -0.4-
-0. -0.5- -0.5 -0.5- - -0.5- -0.5-
-0.- -0.6- _ -0.6- -0.& -0.6- -0.6-
-0.7 -0.7- - -0.7- - - -0.7- .0.7- -0.7-
-0.: -0.8- -0.8- -0.8- -0.& -0.8-
-0.' -0.9- -0.9- -0.9- -0.9- -0.9-
-1.1 -1.0- -1.& -1.0- -1.0- -1.0-
-1.1 -1.1- -1.1- -1.1- -1.1' -1.1-
-1.2 -1.2- -1.2- -1.2- -1.2- -1.2-
-
-1. -1.3- -1.3- -1.3- -1.3- -1.3-
-1. -1.4- -1.4- -1.4- -1.4- -1.4-
-1. - -1.5- -1.5--- -1.5- -1.5- -1.5
L M H R L M R L M H R L M R L M H R L M R
zone zone Zone SO TO zone Zone
Figure 8. Change in sediment elevation (ft, MLLW) over time monitored at rods installed in previous bioturbation study. H. area of high wave
energy reduction by the wavebreak; M = medium; L = low; R = reference (no wave energy reduction). Error bars represent± one
standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 26

Table 4. One-way ANOVA testing differences in sediment elevation (ft, MLLW)from rods installed at
previous bioturbation patches among all combinations of surveys. Survey 1 = May 2016,
Survey 2 =January 2017, Survey 3 = October 2017, Survey 4= May 2018.
Wave energy Survey 1 4 2 Survey 1->3 Survey 1 4 4 Survey 2->3 Survey 2->4 Survey 3 4 4
reduction
Reference(none) ND ND C,B ND A ND
Low ND ND C ND B ND
Medium ND ND A,B ND A ND
High ND A A
Shaded bars=significant effect at P<_0.05;comparisons with the same letters are not significantly different. ND=no significant
difference.Cells with no information represent strata where rods could not be located,presumably due to excessive sediment
deposition.
USV Digital Elevation Model: The USV collected bathymetry data across the entire site in June 2016
(Figure 9).The survey was conducted during both flood and ebb tides and real-time tidal corrections
were made to data collected. Water depths ranged from 0.7 to 1.6 m (2.3 to 5.2 ft) across the site.The
western portion of the site was notably shallower than the eastern portion. The USV will collect
bathymetry data during the final monitoring survey and data will be compared to this baseline
bathymetry.
wavebreak
c.:11 C , ,C, _The.- s, .__-____7 -...
3957000 .
U
o A04 / °� •/ Ills
3956800- 1 i` L0• , z
7
-
3968800 , o �� z
,�� ,, --�0.9
.•s o ,
•
-,06
• . o
1 b
v:
p o O
'O, v i 0.6
3956400- Ot o
0
:)c'. ® o J 0.4
03
3956200- 2`,
o co
vo 09 ,
1
3956000
446600 446800 447000 447200
Figure 9. Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital elevation
model at the Bonner Bridge Seagrass Mitigation Site prior to construction of the wavebreak
(ultimate location of wavebreak shown). Soundings are in MLLW.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 27

Near-field Wall Sediment Elevation Survey: The surveys conducted by SEPI revealed significant scour
pits having formed under the wavebreak units themselves.This sediment is suspected to be the source
of the light colored band visible to the south of the wall in aerial images (Figure 3). The 5 transects were
treated as replicates for evaluating sediment elevation on both the north and south sides of the
wavebreak, by distance. A comparison of sediment elevations by distance and side of wall (north vs
south) shows a generally consistent pattern of erosion in the immediate proximity of the wall but with
little change in sediment elevation with distance on either side of the wavebreak(Figure 10a through h).
There,transects on the south side of the wall however,generally appeared to be shallower. Upon
examination under 2-way ANOVA (Table 5)there was no significant interaction of the main effects
(distance, side), allowing each main effect to be re-tested independently.The effect of distance
irrespective of side was significant (P<0.05) at every survey time. However, the visually apparent
difference in elevation among the north and south sides of the wall was statistically significant beginning
in January of 2018 and remained different (but for April of 2018) through June of 2018, with the
southern side being consistently shallower. To further examine for pattern of differences with distance,
it was noted that the 0 distance (immediately abutting the wall structure) was always the deepest,
followed closely by the 5 foot distance being the next deepest for the first three surveys. Some spatially
inconsistent differences in elevation among distance occurred during other surveys (Table 5) but the
0 and 5 distances always remained the deepest.
Table 5. Results of 2-way ANOVA for the near-field sediment elevation (ft, MLLW) by survey.
Year 2017 2017 2018 2018 2018 2018 2018 2018
Month June September Jan Feb March April May June
Distance <.0001 <.0001 <.0001 0.0006 <.0001 <.0001 <.0001 0.0005
Side 0.7046 0.6983 0.0494 0.0011 0.0372 0.0608 0.0002 0.0002
Interaction 0.8913 0.9754 0.3347 0.777 0.118 0.0744 0.4098 0.8185
South side significantly shallower?
ANOVA Comparison no no no yes yes yes yes yes
Distance 75,10 and 100 also Distance 100 was as
Distance 0 deepest,deeper than 5 and both significantly shallower than other shallow as S but both
significantly deeper than rest? distances but equal to 5 and shallower shallower than 0(which
than 0(which was deepest)? was deepest)?
ANOVA Comparison yes yes yes yes yes yes yes yes
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 28

JUNE 2017
elevation ftMEAN
5'
4'
3'
2'
1
-2
-3
1 II pi PP
-5
-6
-7
-8
-9
-1C
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10a. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 29

SEPTEMBER 2017
elevation_ftMEAN
5'
4'
3'
2'
0
I pp op
-5
-6
-7
-8
-9
-1C
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 1Ob. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are ± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 30

JANUARY 2018
elevation_ft MEAN
5'
4'
3'
2'
1'
7 ,� 1111101-711117-T- _ I
_
-5
-G
-T
-1C
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10c. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are ± 1 standard deviation.
C5A-NCDOT-FL-18-1830-2845-09-REP-01-FIN 31

FEBRUARY 2018
elevation_ft MEAN
5'
4'
3'
2'
-3 —
-4
-5
-6
-7
-8
-4
-SC
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10d. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 32

MARCH 2018
elevation ftMEAN
5'
4'
3'
2'
1'
r. 111;774—op po go 11 II pi pp pi pi
-3
-5
-6
-7
-S
-4
-1C
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10e. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 33

APRIL 2018
elevation_h MEAN
5'
4'
3'
2'
1
'pip I pi gm
-2 ��,y
-3 T
-4
-5
-6
-7
-g
-9
-1�
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10f. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are ± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 34

MAY 2018
eIevation_ft MEAN
5'
4'
3'
2'
1'
-z0 1 1
L or
f
-3
-4
-5
-6
-7
-9
-10
north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100
Figure 10g. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 35

JUNE2018
elevation ft MEAN
5'
4'
3'
2'
JUIIhIh1hIh1hlJ! 111 !1
4 Ili
-5'
-7.
-g
-1t1
north south north south north south north south north south north south north south north south north south north south north south north south north south north south north south
0 5 10 15 20 25 30 35 40 45 50 75 100 125 150
Figure 10h. Average sediment elevation (ft, MLLW) by side of wavebreak and distance over time. Error bars are ± 1 standard deviation.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 36

Wave Regime and Model Validation
Long Term Wave Regime: After the wavebreak was installed, pressure sensors were installed at
specified stationary locations on both the north and south sides of the wavebreak to spatially assess
significant wave height (highest 1/3 of waves) distribution arising from the top 5% of wind events
between the two sides of the wavebreak. Figure ila shows the significant wave height for the north
side during the 2017 deployment and Figure 11b shows the wave height pattern for the south side
during that same deployment. Figure 12a shows the wave height for the north side during the 2018
deployment through May and Figure 12b shows the wave height pattern for the south side during that
same deployment. Figures 13a and b show the difference in the significant wave heights over elapsed
time. During 2017,there did not appear to be a substantial difference in the significant wave heights
among the two sides, whereas in 2018, events where the significant wave height was higher on the
south side of the wall were more numerous and of greater difference over time.This indicates that wave
events were often higher on the south side than the north, suggesting that the north side of the wall
could also be receiving substantial sheltering from waves.
WEMo model validation: Wave forecast modeling using WEMo was initially conducted in January 2016
for different lengths of the wavebreak structure. Modeling was re-analyzed in January 2017 after
installation of the 500 ft(152 m)wavebreak (Appendix I). As done previously,the model was run on
65-foot (20-meter) grid cells, as the bathymetric data which are an important driver of the calculations is
not more resolved than that distance. Forecast acreage of seagrass was computed by regression from
the relationship of wave energy to seagrass cover(Fonseca and Bell 1998).The area of the seafloor
experiencing at least a 5% reduction in wave energy was computed. The total acreage associated with
the zones of wave reduction beyond the 5%threshold is given in Table 6.Theoretically, this could result
in an overall total of 1.78 acres (0.72 hectares) of new seagrass with the 10% reduction zone producing
1.13 acres (0.46 hectares) and the 5% reduction zone producing 1.50 acres (0.61 hectares).
Table 6. Areas for the wave energy reduction zones depicted in Appendix I in both acres and square
meters.
Percent Representative Wave Energy Reduction Square Meters Acres
>66% 3,184 0.8
33%to 66% 21,153 5.2
5%to 33% 200,889 49.6
<5% 1,095,260 270.6
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 37

a North Side January—July 2017
ON
ON ,
O•O
•
Ob •
pb. 1
0264 • : i i .
I i
T Tt
1 �
.iiililf.
11. .1.1. 1 ' .iiiil. 1..
1 , q. ., ft, . .?. . t
... ikii:It,I ..
�' •
k
T, • I..i,,.; II iiff .L.: . . I • .• . ;'
11 , Z ' J •}•
1 is.14 f
•
0 06. iiii '
b South Side January—July 2017
ON
OM
•
Ow 7 1
•
. ! ; 1 •
0 at .
•
.k '
•il .
Ob
•
• •
I ii ! ,
I i i ' ' ' •
i'9. 4 i ;
i..
1t • ' 'I , '... • :1 /13/4
, . III • 3 ;r• )1,
4
lil
_ • 1
,�
Figure 11. Hourly significant wave heights (m) measured at the wavebreak from January through July 2017 for(a)Top- north side of the
wavebreak and (b) Bottom -south side of the wavebreak. Htime =elapased time in hours.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 38

•
a North Side January— May 2018
li.W_M
oW
0M.
0 40
OM •
I •
OM
020 • i
I
I .0 le
•
ola ' • i • 1 '1 I •1 i I 11t�, '• r I
• r
O06 rl l �'. •I I'. • ! I. '{�
11.00 AflJ 44
b South Side January— May 2018
OM
OM'
•
OM •
•
OM
OM 1
t
Oa , 1
f , 1 ,
Ou
ow 1 • � r I 1 •;1
!I 1 I t •
ow' I
,MO lone pO
MM.
Figure 12. Hourly significant wave heights (m) measured at the wavebreak structure from January through May 2018 for(a)Top- north side of
the wavebreak and (b) Bottom-south side of the wavebreak. Htime =elapased time in hours.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 39

DIFF IN SIG WAVE HEIGHTS: POSITIVE VALUE = NORTH HIGHER while NEGATIVE VALUE = SOUTH HIGHER Jan -July 2017
a
on
o 1e. j # • ` • is .•_i •• •• I:.• i r , 1 •f ;7• t •t i
�� •1: •t . 1. ��p.\♦ r t(4'i Y •. .rylvt ? ., ' • • t • . - t
om W.;
.:.. • lr ••••1 y • . �i.3 } • ' ;• J.,,, ,,. .4 j'I • . ; t3!6,.y' . •, 'ii �4r!!•G. • ! 3 ,.tiask. :,}i � t ..•. iii :i i }. sl.,. :.i � + b S .} i,t�f.�;��'t•�. [owI • I) ')1 !{iiiv.': •• `I,}'.t :4• •A• 4t4.-,i i. rll 1. .;4:• ••••. f-•044. �itj. 1:.4p..: tsis•rzik.4 lc••_ t :t4' } 0 FT •., 1 r • •' •• •:s• 1). .•'i •- Si f • ;•C.i -} ,., , • �f'.• •: .s . • ••i: �'y`' L(
4f +� :�� '. �:t ;fit � �: �i��r. ..' � it �} iN'f ;,iW;�. ,{.r. ri;vt
• , : } . 'h y , •
ou• ••
:1 .
0s
o a,r .
WOO ION
a•• .. tnu
DIFF IN SIG WAVE HEIGHTS: POSITIVE VALUE = NORTH HIGHER while NEGATIVE VALUE = SOUTH HIGHER Jan -May 2018
b
o»
016• •
pj i
•
o•o. F, t •• •
I . . ,
.j it :
• •on �� �' I!• l •• t• YI•1R )Frf' • :; 1.t i': �• ja i • � • 4 .*;:hF i + � '1 `.. --
• • • {l } .• j i . t ! t..
1irki
o•• •t ,, s ? ti. IFS' .y .r .• .ti'• . .S
s
t , •
o.e•
os•
MO IOW •-
Yam
Figure 13. Difference in hourly significant wave heights (m) measured at the wavebreak structure for (a)Top -Jannuary through July 2017 and
(b) Bottom -January through May 2018. Htime = elapased time in hours.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 40

After the model was run and a smoothing technique (krigging) applied (Appendix I), there is the
appearance of a disruption in the wave reduction just south of the wall. However, this is a product of the
krigging and that small zone of 33-66%wave reduction just south of the wall is a display artifact and was
not part of the acreage calculations.
In May 2018, scientists observed patchy seagrass habitat consisting of three species of seagrass (Zostera
marina, Halodule wrightii, and Ruppia maritima). Halodule wrightii and Z. marina were both commonly
observed while R. maritima was rarely observed.The major substrate type observed throughout the site
was fine siliceous sand. Limited vessel traffic was observed during on-site surveys within the immediate
vicinity. Site conditions were relatively consistent during the survey,with slight variations due to
direction and strength of the wind. Average daily water temperatures during the survey ranged from
23.4°C (74.2°F)to 24.8°C (76.7°F),with wind speeds ranging from 7.6 to 41.1 kph (4.7to 25.5 mph). Wind
direction was predominately south-southwest.
Epibiota Monitoring
During the January 2017 baseline survey, ebb tides were extremely low and monitoring stations at all
three elevation strata (high, middle,and low) were exposed above water. No biota had colonized the
substrate and the percent cover of concrete and rock were both 100% during this survey.
During the May 2018 survey,there was a consistent south/southwest wind that resulted in high water
levels at the structure, even at ebb tide. Monitoring stations at the high elevation were exposed above
water but were primarily wet and regularly splashed by waves hitting the structure during all tidal stages
observed (Photos 12 and 13).The middle elevation monitoring stations were exposed above water
during all tidal stages observed, also primarily wet, and regularly splashed by waves hitting the structure
(Photos 14 and 15).The low elevation monitoring stations were completely submerged at all tidal stages
observed, even ebb tide. Due to high levels of turbidity in the water column during the survey,the low
strata monitoring stations were photographed at a closer distance than the high and middle strata,
requiring four close-up photographs per station which were later mosaicked together(Photos 16
and 17).
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 41

400
1�., 91 ,
th. ,,... . ,, . ....... . ,, ...r... --t-ai• * -'. PI
F --I I
111166111111M101011016/A'
•
Photo 12. Representative photo of rock substrate for a high elevation monitoring station (Station 35)
showing wet rock on the structure at the Bonner Bridge Seagrass Mitigation Site during the
May 2018 survey.
i
_j har<N�-u ., c, . , .-.:. ,.. ... .
II r
[116.-,.' - ' 111
Photo 13. Representative photo of concrete substrate for a high elevation monitoring station
(Station 35) showing wet concrete on the structure at the Bonner Bridge Seagrass Mitigation
Site during the May 2018 survey.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 42

7 l° LJ`
u �.
•
.Y\
Photo 14. Representative photo of rock substrate for a middle elevation monitoring station (Station 28)
showing wet rock, algae, and barnacle growth on the structure at the Bonner Bridge Seagrass
Mitigation Site during the May 2018 survey.
log
- . . - .-,
•
Photo 15. Representative photo of concrete substrate for a middle elevation monitoring station
(Station 28) showing wet concrete, algae, and barnacle growth on the structure at the
Bonner Bridge Seagrass Mitigation Site during the May 2018 survey.
CSA-NCDOT-FL-18-1830-2845-09-REP-0I-FIN 43

- 1IIIIIIIIIIIII11■ir
Photo 16. Representative photo mosaic of rock substrate for a low elevation monitoring station
(Station 1) showing submerged rock and barnacle growth on the structure at the Bonner
Bridge Seagrass Mitigation Site during the January 2017 survey.
I
i
1+xAr
I
1
Photo 17. Representative photo mosaic of concrete substrate for a low elevation monitoring station
(Station 1) showing submerged concrete and barnacle growth on the structure at the Bonner
Bridge Seagrass Mitigation Site during the January 2017 survey.
Mean percent cover of colonizing biota and non-living substrate (concrete or rock) were assessed at the
60 fixed monitoring stations along the wave break structure. Data was grouped first by substrate type
(concrete or rock),then by strata (high, middle, or low),and also by orientation (north or south side of
the structure). Data collected for concrete and rock monitoring stations are displayed in Tables 7 and 8,
respectively.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 44

Table 7. Percent cover of biota and concrete from concrete monitoring stations during the Baseline Monitoring Survey in January 2017 and
the Year 1 Annual Monitoring Survey in May 2018.
Concrete-North Concrete-South
Biota or Non-Living Substrate 2017 2018 2017 2018
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0.00 0.00 0.00 34.12 41.11 20.14 0.00 0.00 0.00 14.51 14.49 16.81
Barnacle 0.00 0.00 0.00 5.51 37.61 64.03 0.00 0.00 0.00 0.00 46.67 73.01
Hydroid 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6.64
Oyster 0.00 0.00 0.00 0.00 0.58 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Non-living substrate
Concrete 100.00 100.00 100.00 60.37 20.70 15.83 100.00 100.00 100.00 85.49 38.84 3.54
Rock 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Major categories
TOTAL BIOTA 0.00 0.00 0.00 39.63 79.30 84.17 0.00 0.00 0.00 14.51 61.16 96.46
TOTAL NON-LIVING SUBSTRATE 100.00 100.00 100.00 60.37 20.70 15.83 100.00 100.00 100.00 85.49 38.84 3.54
Table 8. Percent cover of biota and rock from rock monitoring stations during the Baseline Monitoring Survey in January 2017 and the Year 1
Annual Monitoring Survey in May 2018.
Rock-North Rock-South
Biota or Non-Living Substrate 2017 2018 2017 2018
High Middle Low High Middle Low High Middle Low High Middle Low
Biota
Macroalgae 0.00 0.00 0.00 0.00 5.06 1.35 0.00 0.00 0.00 0.00 0.00 1.41
Barnacle 0.00 0.00 0.00 0.00 29.11 14.86 0.00 0.00 0.00 0.00 3.51 16.90
Hydroid 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Oyster 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Non-living substrate
Concrete 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Rock 100.00 100.00 100.00 100.00 65.82 83.78 100.00 100.00 100.00 100.00 96.49 81.69
Major categories
TOTAL BIOTA 0.00 0.00 0.00 0.00 34.17 16.21 0.00 0.00 0.00 0.00 3.51 18.31
TOTAL NON-LIVING SUBSTRATE 100.00 100.00 100.00 100.00 65.82 83.78 100.00 100.00 100.00 100.00 96.49 81.69
CSA-NCDOT-FL-18-1830-2845-09-REP-0I-FIN 45

Colonizing biota observed on concrete substrate included barnacles, macroalgae (primarily unidentified
green hair algae), hydroids, and oysters. For concrete stations, biotic colonization was dominated by
barnacles for the majority of strata. Percent cover of barnacles increased the most between the two
surveys on the low strata,with maximum percent cover of 64.03% and 73.0%for the north and south
sides, respectively(Table 7). Percent cover of macroalgae was greater than barnacles on high and
medium strata on the north side and high strata only on the south side,with a maximum percent cover
of 34.1%for high strata on the north side. Hydroids were only present on low strata on the south side,
with percent cover of 6.6%, while oysters were only present on middle strata on the north side but
negligible at<1%cover.
Colonizing biota on rock substrate only included barnacles and macroalgae; no hydroids or oysters were
observed on either side of the structure. For rock stations, biotic colonization was dominated by
barnacles for the majority of strata, with maximum cover of 29.1%on middle strata on the north side
(Table 8). Unlike concrete, percent cover of macroalgae was generally low and not greater than
barnacles on high and medium strata. Maximum percent cover of macroalgae on rock was 5.1%for
middle strata on the north side.
For all elevation strata, concrete exhibited greater total colonization by biota versus rock on both north
and south sides of the structure. For both concrete and rock,the middle and low strata generally
showed greater colonization by biota than high strata, likely due to fact the high strata were never
submerged,thus preventing initial colonization or survivorship due to desiccation.
Comparison of north versus south sides of the structure revealed that percent cover of total biota was
higher on the north side for high and middle strata for both concrete and rock; while it was higher on
the south side for low strata for both substrates (Tables 7 and 8). More specifically, macroalgae was
higher in cover on the north side among all strata and for both substrates. Barnacles colonizing rocks
were also more prevalent on the north side of the structure, while those on concrete did not display any
discernable orientation preferences between north and south sides. Hydroids and oysters were not
present in numbers high enough to make any determination of orientation preference.
4.0 Conclusions
The wavebreak has been successfully installed as of January 2017 (Photo 18) and passed its
post-construction engineering inspection. Monitoring will continue for an additional four years(Table 1)
which will build off of this post-installation report.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 46

e aE
Photo 18. North-oriented view of the wavebreak installed in January 2017 at the Bonner Bridge
Seagrass Mitigation Site.The total structure length is 500 ft (152 m).
Seagrasses were successfully relocated from the construction corridor to two planting zones south of
the wall footprint in May 2016. Seagrasses in the area are composed of all three of the marine species
found in North Carolina (mixed Halodule wrightii, Ruppia maritima, Zostera marina). Seagrass cover •
measured within the confines of natural, colonized seagrass displayed dramatic change from May 2016
to January 2017 (-42%). The relocated seagrass area showed a similar decline of-35.0%. It cannot yet be
determined if this change is a typical seasonal change in cover(spring versus winter) or if there was a
contribution from Hurricane Matthew. The hurricane passed over this area on October 9, 2016, prior to
the installation of the wavebreak structure; thus,the relocated area was highly exposed to an extreme
wave event only 5 months after planting which could have led to disruption of the relocated material.
A bioturbation experiment to help determine the relative role of bioturbation versus wave energy
reduction in seagrass space occupation was significantly disrupted by unknown sources. Only 20%of the
mesh (8 out of 40 remesh sheets)was relocated during the January 2017 survey.The wavebreak was not
present during this time so comparisons could only be tested among the remaining 8 remesh sheets and
those edges that did not receive remesh. There was no significant difference (p<0.05) among the
change in distance between the remesh and no remesh treatments, preliminarily indicating that
bioturbation was not strongly influencing the expansion of patch margins at that time. However,the
passage of Hurricane Matthew may have obscured effects (disturbance effects like Hurricane Matthew
erode seagrass patches from their edge, much like sting ray bioturbation; Fonseca et al., 2000).
Physical data collection of sediment elevation and wave energy has been completed. A digital elevation
model of the site was collected using the USV and these data will be compared with an end-of-project
survey conducted in the same manner to determine net sediment accumulation or loss in the project
area. Sediment elevation stakes will also continue be monitored to gain an understanding of shorter
term fluctuations in sediment elevation. An overall change in sediment elevation (-4.1 cm)was detected
which cannot be attributed to the wavebreak, as similar differences occurred across the entire shoal.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 47

The final wave modeling effort indicated that theoretically,the wavebreak influence on seagrass cover
could result in a total of 1.78 acres (0.72 hectares) of new seagrass overall, with the 10% reduction zone
producing 1.13 acres (0.46 hectares) and the 5% percent reduction zone producing 1.50 acres
(0.61 hectares).The classification resulted in 33.4 acres(13.5 hectares) seagrass cover across the Bonner
Bridge Seagrass Mitigation Site. Aerial imagery will be collected and analyzed annually to capture
changes in seagrass cover associated with the addition of the wavebreak structure.
Finally,time-zero data collection for epibiotic colonization was completed using a stratified random,
repeated measures design. As expected, there was no discernible epibiotic colonization in any of the
120 digital images recorded. Photographs of the exact locations on the structures, stratified by tidal
elevation and north and south sides of the wall will be repeated over time to quantify epibiotic
colonization trajectory, abundance and composition.The May 2018 data collection for epibiotic
colonization was completed using a stratified random, repeated measures design. During the May 2018
survey,the percent cover of concrete and rock decreased from levels observed in January 2017 as
epibiota colonized the structure. Concrete typically exhibited greater colonization by macroalgae and
fauna than the rock substrate.The middle and low strata of both concrete and rock showed greater
colonization than the high strata. Photographs of the exact locations on the structures, stratified by tidal
elevation and north and south sides of the wall will continue to be monitored over time to quantify
epibiotic colonization trajectory, abundance and composition.
5.0 References
Bohnsack,J.A. 1979. Photographic quantitative sampling of hard-bottom benthic communities. Bulletin
of Marine Science 29:242-252.
https://www.researchgate.net/publication/233545259 Photographic Quantitative Sampling o
f Hard-Bottom Benthic Communities
Braun-Blanquet,J. 1972. Plant sociology: the study of plant communities. Hafner. New York, NY.
https://archive.org/details/plantsociologyst00brau
CSA Ocean Sciences Inc. 2017. B-2500 Bonner Bridge Seagrass Mitigation Site As-Built Report.
CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN.
Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near Beaufort,
NC, USA. Marine Ecology Progress Series 171:109-121.
Fonseca, M.S., W.J. Kenworthy, and G.W.Thayer. 1998. Guidelines for the conservation and restoration
of seagrass in the United States and adjacent waters. NOAA COP/Decision Analysis Series.
222 pp. http://docs.lib.noaa.gov/noaa documents/NOS/NCCOS/COP/DAS/DAS 12.pdf
Fonseca, M.S., W.J. Kenworthy, and P.E. Whitfield. 2000.Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biologia Marina
Mediterranea 7:373-376.
Fonseca, M.S., P.E. Whitfield, N.M. Kelly, and S.S. Bell. 2002. Modeling seagrass landscape pattern and
associated ecological attributes. Ecological Applications. 12:218-237.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 48

Fonseca, M.S., M.A.R. Koehl, and B.S. Kopp. 2007. Biomechanical factors contributing to
self-organization in seagrass landscapes. Journal of Experimental Marine Biology and Ecology
340:227-246.
Fourqurean,J.W., A. Willsie, and C.D. Rose. 2001. Spatial and temporal pattern in seagrass community
composition and productivity in south Florida. Marine Biology 138:341-354.
http://seagrass.fiu.edu/resources/publications/Reprints/Fourqurean%20et%20a1%202001%20M
arine%20Biology.PDF
Kelly, N.M., M.S. Fonseca, and P.E. Whitfield. 2001. Predictive mapping for management of seagrass
beds. Aquatic Conservation Marine and Freshwater Ecosystems 11:437-451.
Kenworthy, W.J. and A. Schwarzchild. 1997. Vertical growth and short shoot demography in Syringodium
filiforme in outer Florida Bay, USA. Marine Ecology Progress Series 173:25-37. https://www.int-
res.com/articles/meps/173/m173p025.pdf
Kohler, K.E. and S.M. Gill. 2006. Coral Point Count with Excel extensions(CPCe): A Visual Basic program
for the determination of coral and substrate coverage using random point count methodology.
Computers and Geosciences 32(9):1,259-1,269.
Malhotra, A. and M.S. Fonseca. 2007.WEMo (Wave Exposure Model): Formulation, Procedures and
Validation. NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
https://repository.library.noaa.gov/view/noaa/9331
SEPI Engineering&Construction. 2016. Complete Construction Plans.
Thayer,G.W., W.J. Kenworthy and M.S. Fonseca 1984. The ecology of eelgrass meadows of the Atlantic
coast: A community profile. U.S. Fish and Wildlife Service. FWS/OBS-84/02.
https://www.nwrc.usgs.gov/techrpt/84-02.pdf
Townsend, E. and M.S. Fonseca. 1998. The influence of bioturbation on seagrass landscape patterns.
Marine Ecology Progress Series 169:123-132. https://www.int-
res.com/articles/meps/169/m169p123.pdf
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 49

Appendix I
Project Site Selection
In 2015, CSA completed the process of site selection ([Report] Table 1). Existing seagrass cover and site
conditions were compared between potential mitigation sites within the Pamlico Sound in the vicinity
(^' 8 km [—5 mi]) of the Oregon Inlet.The Bonner Bridge Seagrass Mitigation Site was identified on a
historically stable shoal, where seagrass growth was evident, and had the most potential for increased
seagrass cover with gap closure among existing patches of the sites examined.The site was located near
dredge spoil islands approximately 4.8 km (3 mi) southwest of the existing Bonner Bridge at Oregon
Inlet. Wave and seagrass response models techniques were performed to determine the length of the
wavebreak forecast to achieve the 1.28 acres (0.52 hectares) of seagrass mitigation.
Also in 2015, CSA completed development of the wavebreak design and placement, a task which
required both wave forecasting, seagrass recovery forecasting and engineering sub consultation for
placement of the structure design. Wave forecast modeling(Malhotra and Fonseca, 2007) was utilized
to estimate the wave reduction effects of the wavebreak structure. Percent wave reduction was
computed from comparisons of no-wavebreak and wavebreak modeling scenarios for various length
wavebreak structures.The percent wave energy reduction for a given length wavebreak was converted
to percent seagrass cover(recomputed from Fonseca and Bell, 1998)to predict the overall increase in
seagrass acreage across the site as the result of wave reduction.The 500-foot(152-meter) long wall was
designed with an inverted "V-shape"consisting of two 250-foot(76.2-meter) sections.
The V-shape was a professional judgement on the part of the design team to mitigate wave impacts on
the wall from the forecast direction of maximum wave height development (northerly).Thus,the
wavebreak was oriented on the site to attenuate the dominant north and northeasterly exceedance
event (wind events composing the local top 5%of all hourly wind speeds, along with their direction,
over the preceding three years period) winds and create a calmer environment on the lee side (south
facing side) of the structure to promote seagrass patch coalescence and new, permanent seagrass
acreage.
Once the 500-foot (152-meter)wall length was selected by NCDOT(the wall length that most closely
approximated the forecast 1.28 acres [0.52 hectares] of new seagrass cover), four wave energy regimes
(treatments)were defined from a cumulative frequency analysis of the area covered by the modeling
effort where greater than 5%energy reduction was forecast to occur as the result of the wavebreak
(Figure I-1).The wave energy regimes represent high wave energy reduction (>66%forecast reduction),
moderate reduction (34 to 66%), low reduction (5 to 33%), and ambient or reference (<5% reduction).
These wave energy reduction regimes became strata for random selection of various sampling described
below.
CSA-NCDOT-FL-18-1830-1845-09-REP-01-FIN 1

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Figure I-1. Post-construction forecast of wave energy(RWE; representative wave energy [J m-1 wave
crest]) based on 500-foot (152-meter) wavebreak structure, superimposed on image of
seagrass cover.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 1-2

Project Engineering and Design
CSA subcontracted SEPI Engineering to design the wavebreak and provide the engineering Signed and
Sealed Design Plans.The wavebreak was designed based on wave height forecasts provided by CSA
using the WEMo model (Malhotra and Fonseca, 2007) and the aforementioned exceedance event winds.
To meet the 500-foot (152-meter) design length,the structure was composed of 101 individual
"Reefmaker" units each containing a central piling, one concrete base unit, and three concrete wave
attenuator units stacked on the base unit and each embedded with natural granite rock to increase
surface area for epibiota colonization (each unit was 4.8 ft x 4.8 ft x 4 ft [1.46 m x 1.46 m x 1.22 m])
(Photos I-1 and 1-2). Granite rock was chosen to prevent bioerosion of the enhanced surface area. Each
Reefmaker unit had a bottom clamp and a top collar installed to secure the concrete layers to the
central piling to hold the base and wave attenuator units in a fixed vertical position on the piling,
preventing settling into the sand substrate over time.
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Photo I-1. East-facing view of installation of the central pilings with piling clamps at the Bonner Bridge
Seagrass Mitigation Site.Yellow arrow points to an installed clamp.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 1-3

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Photo 1-2. One Reefmaker unit consisting of one base unit on the bottom and three wave attenuator
units containing granite rock. One hundred and one of these units were installed at the
Bonner Bridge Seagrass Mitigation Site. For scale,the width of the units is 4.8 ft (1.46 m).
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 1-4

Appendix II
Bioturbation Experiment
To evaluate the influence of biological disturbance on seagrass patches at the site (sensu Townsend and
Fonseca, 1998), CSA installed a bioturbation exclusion experiment in May 2016.There, 40 locations were
randomly selected from within strata (10 per strata) defined by the forecasted wave reduction pattern
following wavebreak placement (high wave energy reduction =>66%; moderate reduction = 34 to 66%,
low reduction = 5 to 33%, and ambient or reference=<5% reduction) (Figure II-1). The nearest isolated
seagrass patch to that location was then selected for application of the experimental treatment. At the
center of all 40 patches, a 2.4-meter(8-foot) long stainless steel rod (Photo II-1)was driven into the
sediment until only 3 to 10 cm (1 to 4 in) remained above the sediment. Five randomly selected patches
were assigned wire mesh (wire remesh panels 1.07 m x 2.13 m [42 in x 84 in])welded steel wire remesh
sheet (with 0.106 m x 0.1.06 m [4 in x 4 in] mesh size)to exclude bioturbating sting rays and five were
un-protected within each of the four wave energy regimes (total of 40 patches). At each of two
randomly selected cardinal directions per patch, the distance from the center rod to the edge of the
seagrass was measured in centimeters using a metric tape (Photo 11-2). For patches receiving mesh, each
of the cardinal directions received a wire mesh.The longest length of the mesh was positioned parallel
to the patch edge approximately 1/3 on seagrass and 2/3 on sand to allow room for seagrass growth
(Photo II-3).Two J-shaped rebar stakes 0.3 m (1 ft) long anchored the mesh so it was flush on the
seafloor. Flush deployment on the seafloor and anchoring were performed to prevent entanglement by
sea life, such as diving birds. Other information recorded for each patch included the treatment received
(mesh or no mesh), elevation of the rod above the sediment, and seagrass species observed at each
edge. Change in the distance from the center rod to the patch margin will be recorded over time.The
statistical approach for this experiment is a repeated measures two-way analysis of variance with wave
energy and patch protection as main effects.The mesh and stakes will be removed and disposed of
appropriately when patch coalescence begins, at which time monitoring of these patches will cease.
During the May 2018 survey, scientists revisited each patch to collect data. Scientists navigated to the
location of the center rod using the Trimble GPS. Once on location, they searched for the center rod
using a glass bottom bucket and grazing a rake (tines up) on the seafloor.The distance from the center
rod to the edge of the seagrass patch was re-measured along the same cardinal directions established
during installation.The presence or absence of mesh, elevation of the rod above the sediment, and
seagrass species observed at each edge was also noted for each patch.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN II-1

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Photo II-1. Center rods (2.4 m [8 ft]) installed at each bioturbation experiment patch within the Bonner
Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 11-2

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Figure II-1. Randomized distribution of the seagrass patches and the experimental treatments
selected for use in the bioturbation study.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN II-3

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selected direction at the Bonner Bridge Seagrass Mitigation Site.
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Photo 11-3. Exclusion mesh installed flush on the seafloor on the edge of the seagrass patch within the
Bonner Bridge Seagrass Mitigation Site. Mesh size is 0.106 m x 0.1.06 m (4 in x 4 in).
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 11-4

Bioturbation Experiment
At the time of setting out the experiment in May 2016,the average distance from the center rod to the
edge of all 40 patches was 3.8 m (12.5 ft) (Table II-1). At the onset of the experiment patches with
exclusion mesh had an average distance of 3.9 m (12.8 ft) and patches without exclusion mesh had an
average distance of 3.7 m (12.1 ft).
Table II-1. Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment. Updated July 2018; n/a = not applicable; meshes had been
removed. ND = no data; distances not measured as experiment had ended.
Survey All 40 patches(m) Patches with Patches without
exclusion mesh (m) exclusion mesh(m)
May 2016 3.8 3.9 3.7
January 2017 3.5 3.7 3.3
October 2017 1.48 n/a n/a
May 2018 ND ND ND
In January 2017, all 40 bioturbation patches were revisited and monitored. For all 40 patches,the
average distance from the center rod to the edge of the patch was 3.5 m (11.5 ft). For all mesh
treatment patches,the average distance to the edge of the patch was 3.7 m (12.1 ft) (however, mesh
was only located at 8 locations within 7 patches at the time of the survey). Patches without exclusion
mesh had an average distance of 3.3 m (10.8 ft). In October 2017, the number of monitored patches was
reduced to 14 to revisit only those 7 patches that still contained mesh at the time of the January survey
in addition to an equal number of non-mesh patches (n=7). Average distance from the center rod to the
edge of all 14 monitored seagrass patches was 1.5 m (4.9 ft). For the 7 patches that contained mesh at
the time of the January survey, the average distance to the edge of the patch was 0.5 m (1.6 ft). The
7 patches without exclusion mesh had an average distance of 1.9 m (6.2 ft). In October of 2017 the
experiment had been terminated and only the distance to patch edges were measured. That distance
had reduced from 3.5 to 1.48 m suggesting the dynamic nature of seagrass patch margins in this area.
CSA-NCDOT-FL-18-1830-2845-09-REP-01-FIN 11-5

41,1-1*
r
GSA
CSA Ocean Sciences Inc. www.csaocean.corn
8502 SW Kansas Avenue Phone: [phone]
Stuart, Florida 34997 Fax: [phone]
29 November 2017
Kathy Herring
North Carolina Department of Transportation
Project Development and Environmental Analysis Unit
Natural Environment Section
1598 Mail Service Center
Raleigh, North Carolina 27699-1598
Subject: Summary of Year 1 Biannual Survey—October 2017—LETTER REPORT
Dear Kathy:
CSA Ocean Sciences Inc. (CSA) conducted the first Biannual Monitoring Survey(Year 1) for the Bonner
Bridge Seagrass Mitigation Site from 2 to 4 October 2017. The Year 1 Biannual Monitoring Survey was
initially scheduled for August 2017; however, due to tropical storm and hurricane activity and
subsequent above-average water depths in Pamlico Sound at the site, the survey was not conducted
until early October 2017. Table 1 describes CSA's previous activities and future scheduled surveys.
Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wavebreak structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation Experiment Initiation May 2016 Complete
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 Nov. 2016 to 18 Jan. 2017 Complete
Post-construction
Baseline Monitoring Survey 14 to 18 Jan. 2017 Complete
Year 1 Biannual Monitoring Survey 2 to 4 Oct. 2017 Complete
Year 2 Biannual Monitoring Surveys May and Sept. 2018 Scheduled
Year 3 Biannual Monitoring Surveys May and Sept. 2019 Scheduled
Year 4 Annual Monitoring Survey July 2020 Scheduled
Year 5 Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.

The Year 1 Biannual Monitoring Survey included:
• Monitoring of relocated seagrass in two planted areas and reference areas;
• Monitoring of selected bioturbation experiment stations and removal of mesh when found;
• Collection of sediment elevation data;
• Download of long-term wave data and maintenance of wave sensors;
• Collection of wave sensor data throughout the site for future WEMo validation; and
• Maintenance of epibiota monitoring stations on the wavebreak structure.
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina; September 2015) referenced in the
permit(Permit Modification No. 106-12) to ensure all monitoring requirements were met.
During the October 2017 survey, scientists observed patchy seagrass habitat consisting of three species
of seagrass (Zostera marina, Halodule wrightii, and Ruppia maritima). Halodule wrightii was the most
prevalent species, followed by Z. marina and then R. maritima.The major substrate type observed
throughout the site was fine sand. Limited vessel traffic was observed during on-site surveys within the
immediate vicinity.
Site conditions were relatively consistent during the survey, with slight variations due to direction and
strength of the wind. Average daily water temperatures during the survey ranged from 22°C (72°F)to
23°C(73°F), with wind speeds ranging from 26.5 to 31.3 kph (16.4 to 19.5 mph). Wind direction was
predominately out of the north.
MONITORING OF RELOCATED SEAGRASS
In May 2016, prior to wavebreak structure construction,seagrass patches within the structure footprint
and construction corridor were relocated to two planting areas on the south side of the construction
footprint. The percent cover of seagrass within each planting area and within the surrounding reference
area was evaluated immediately following relocation and during each monitoring survey. In October
2017, at the time of the Year 1 Biannual Monitoring Survey, no seagrasses were present within either
planted area and all relocated seagrasses appear not to have survived. Sand scour from the structure
may have impacted the planted areas. Sediment elevation was notably higher in the planted areas in
the lee of the structure. Average percent cover of total seagrass in reference areas was approximately
62.1% (Table 21); H. wrightii was approximately seven times more abundant than Z. marina. Ruppia
maritima was not observed within the reference stations.
From January to October 2017, seagrass cover decreased by approximately 0.2% in the planted areas,
and increased in the reference area by approximately 55.1%. This increase in the reference area is likely
a result of seasonality in seagrass growth, with higher growth occurring in summer months.
1 The average BB scores were converted to percent cover for each area to allow interpolation of averaged BB scores that fall
between BB scale values(conversion was conducted by regressing the mid-point of percent cover associated within the range
covered by each BB scale value,on the associated BB scale value:Percent Cover=2.8108*[BB]2.2321)
CSA Ocean Sciences Inc. 2 29 November 2017

Table 2. BB scores and associated percent cover for seagrass within the planting and reference areas.
Planting Area Reference Area
Survey
Total Seagrass BB Percent Cover Total Seagrass BB Percent Cover
May 2016 3.0 32.7 3.6 49.1
January 2017 0.2 0.2 1.5 7.0
October 2017 0.0 0.0 4.0 62.1
Difference -0.2 -0.2 2.5 55.1
BIOTURBATION EXPERIMENT
A bioturbation experiment to help determine the relative role of bioturbation (primarily by stingrays)
versus wave energy reduction in seagrass space occupation was significantly disrupted by unknown
sources. Only 20%of the mesh (8 out of 40 remesh sheets) was found during the January 2017 survey.
The passage of Hurricane Matthew in October 2016 and associated high-energy water movement and
sedimentation may have displaced or buried the majority of mesh stations in the experiment. In
October 2017, 6 out of the 8 remaining mesh sheets were found and removed following data collection.
At the on-set of the experiment in May 2016,the average distance from the center rod to the edge of all
40 monitored seagrass patches was 3.8 m (12.5 ft) (Table 3). In January 2017, all 40 bioturbation patches
were revisited and monitored. For all 40 patches,the average distance from the center rod to the edge
of the patch was 3.5 m (11.5 ft). For all mesh treatment patches,the average distance to the edge of
the patch was 3.7 m (12.1 ft) (however, mesh was only located at 8 locations within 7 patches at the
time of the survey). Patches without exclusion mesh had an average distance of 3.3 m (10.8 ft). In
October 2017,the number of monitored patches was reduced to 14 to revisit only those 7 patches that
still contained mesh at the time of the January survey in addition to an equal number of non-mesh
patches (n=7). Average distance from the center rod to the edge of all 14 monitored seagrass patches
was 1.5 m (4.9 ft). For the 7 patches that contained mesh at the time of the January survey, the average
distance to the edge of the patch was 0.5 m (1.6 ft). The 7 patches without exclusion mesh had an
average distance of 1.9 m (6.2 ft).
Table 3. Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment.
Survey All Patches(m) Patches With Patches Without
Exclusion Mesh (m) Exclusion Mesh(m)
May 2016 3.8 3.9 3.7
January 2017 3.5 3.7 3.3
October 2017 1.5 0.5 1.9
SEDIMENT ELEVATION
In May 2016, a center rod was installed in the middle of each of the 40 seagrass patches in addition to
4 rods installed in sandy substrate for the bioturbation experiment. In May 2016,the average rod height
within patches was 6.8 cm (2.7 in.) above the sediment and 6.9 cm (2.7 in.) above the sediment within
sandy substrate (Table 4). In January 2017, a total of 32 of the original 40 center rods for seagrass
patches were located,with an average rod height of 11 cm (4.3 in.).Two of the four rods in sandy
substrate were located with an average rod height of 12.4 cm (4.9 in.).
CSA Ocean Sciences Inc. 3 29 November 2017

In October 2017, sediment elevation was monitored at the center rod of the 14 patches monitored for
bioturbation in addition to the original 4 rods in sandy substrate. The center rod was not located (likely
due to burial) at 3 of the 14 seagrass patch locations and 1 sandy substrate location. The average height
of center rods in seagrass patches was 16.6 cm (6.5 in.) and 12.0 cm (4.7 in.) at sandy substrate stations.
Sediment depth has decreased (increased rod height) within seagrass patches and remained similar at
the sandy substrate locations since the Baseline Survey in January 2017.
Table 4. Average rod height in centimeters above the sediment for the bioturbation experiment.
Survey Rods in Center of seagrass Patches(cm) Rods in Sandy Substrate(cm)
May 2016 6.8 6.9
January 2017 11.0 12.4
October 2017 16.6 12.0
WAVE SENSORS
Wave sensors (RBRvirtuoso models) at the two long-term wave energy regime monitoring stations (one
each 25 m north and south of the structure) were retrieved, and data since the last monitoring event
(January 2017) were downloaded. Severe sand impaction in the sensor ports may have influenced
(amplified) actual wave energy; data are under review. One wave sensor was also utilized for WEMo
model validation via systematic relocation across the site to collect data from 24 stations both north and
south of the structure. WEMo computation for these stations and comparison of predicted wave heights
versus observed will follow in future reports, based on water depth and wind conditions of the survey
date versus observed wave heights from the mobile wave sensor.
EPIBIOTIC MONITORING STATIONS
Maintenance of the epibiotic monitoring stations on the structure was completed during the Year 1
Biannual Survey, which entailed the finding and cleaning of permanent monitoring tags and re-etching
of indentations on the concrete to ensure the exact placement of the camera framer during subsequent
surveys. Photographs of each epibiotic monitoring station and subsequent quantitative percent cover
analyses will be performed in all annual surveys.
If you have any questions concerning this report, please feel free to contact me at [phone] or
[e-mail].
Sincerely,
Erin Hodel
Senior Program Manager—Ports, Harbors, & Beaches
CSA Ocean Sciences Inc. 4 29 November 2017

B-2500 Bonner Bridge Seagrass Mitigation Site
Baseline Monitoring Survey
May 2017
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North Carolina Department of Transportation 8502 SW Kansas Avenue
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B-2500 Bonner Bridge Seagrass Mitigation Site
Baseline Monitoring Survey
DOCUMENT NO. CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1
Version Date Description Prepared by: Reviewed by: Approved by:
01 02/24/17 Initial draft for review D. Medellin M. Fonseca
D. Medellin
M. Fonseca
02 04/6/17 Post draft review D. Medellin A. Pittman D. Medellin
M. Fonseca
FIN 05/02/17 Final D. Medellin A. Pittman D. Medellin
M. Fonseca
FIN-REV01 04/06/18 Final revised E.Hodel M. Fonseca M. Fonseca
The electronic PDF version of this document is the Controlled Master Copy at all times.A printed copy is considered to be
uncontrolled and it is the holder's responsibility to ensure that they have the current version.Controlled copies are available
upon request from the Document Production Department.

Table of Contents
Page
List of Tables iv
List of Figures iv
List of Photos v
1.0 Introduction 1
2.0 Actions and Methods 2
Project Site Selection 2
Project Engineering and Design 5
Pre-construction Site Preparation 6
Seagrass Relocation 6
Seagrass Cover 10
Bioturbation Experiment 11
Sediment Elevation 15
Wave Regime and Model Validation 16
Wavebreak Structure 19
3.0 Results 23
Seagrass Relocation 23
Seagrass Cover 25
Bioturbation Experiment 28
Sediment Elevation 28
Wave Energy 30
Structure Epibiota 32
4.0 Conclusions 36
5.0 References 37
CSA-NCDOT-FL-18-1830-2845-07-REP-02-F/N-REV01 iii

List of Tables
Table Page
1 Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation
Site 2
2 Braun-Blanquet scale (score) and percent cover scale values (Braun-Blanquet, 1972) 10
3 BB scores and associating percent cover for seagrass within the planting and
reference areas 23
4 Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment 28
5 Wave energy reduction zones depicted in Figure 1 in both acres and square meters 30
List of Figures
Figure Page
1 Post-construction forecast of wave energy (RWE; representative wave energy
[J m-1 wave crest]) based on 500-foot (152-meter) wavebreak structure,
superimposed on image of seagrass cover 4
2 Aerial image of the wavebreak structure area at the Bonner Bridge Seagrass
Mitigation Site, showing the position of the seagrass planting areas, the
construction corridor and the structure itself. Randomly selected seagrass survey
points are shown for surveys within the planted areas and nearby reference
locations. 7
3 Randomized distribution of the seagrass patches and the experimental treatments
selected for use in the bioturbation study 13
4 Stationary and temporary locations of the pressure sensors at the Bonner Bridge
Seagrass Mitigation Site 17
5 Epibiota monitoring stations on the wavebreak structure at the Bonner Bridge
Seagrass Mitigation Site 21
6 Baseline classification results identifying areas of seagrass (yellow) within the
Bonner Bridge Seagrass Mitigation Site 26
7 Enlarged view of baseline aerial imagery(left) and classification results(right)
identifying areas of seagrass (yellow) within the Bonner Bridge Seagrass Mitigation
Site 27
8 Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital model
at the Bonner Bridge Seagrass Mitigation Site. Soundings are in MLLW 29
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 iv

List of Photos
Photo Page
1 Aerial image of Bonner Bridge 1
2 East-facing view of installation of the central pilings with piling clamps at the Bonner
Bridge Seagrass Mitigation Site 5
3 One Reefmaker unit consisting of one base unit on the bottom and three wave
attenuator units containing granite rock 6
4 Underwater photograph showing harvesting of a Zostera marina-dominated
seagrass sod from within the structure footprint at the Bonner Bridge Seagrass
Mitigation Site 8
5 Image showing placement of a sod in the container for transportation to the
adjacent relocation site at the Bonner Bridge Seagrass Mitigation Site 9
6 Underwater photograph of a planted seagrass sod within the designated relocation
site at the Bonner Bridge Seagrass Mitigation Site moments after installation 9
7 Center rods (2.4 m [8 ft]) installed at each bioturbation experiment patch within the
Bonner Bridge Seagrass Mitigation Site 12
8 Scientists measuring from the center rod to the edge of the seagrass patch on the
randomly selected direction at the Bonner Bridge Seagrass Mitigation Site 14
9 Exclusion mesh installed flush on the seafloor on the edge of the seagrass patch
within the Bonner Bridge Seagrass Mitigation Site 14
10 Inverted "T" shape ruler used to measure rod height above the substrate at the
Bonner Bridge Seagrass Mitigation Site 15
11 Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner
Bridge Seagrass Mitigation Site 16
12 Photograph of one of the two wave senor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site 18
13 Numbered tag installed at every monitoring station on the wavebreak structure at
the Bonner Bridge Seagrass Mitigation Site 22
14 PVC camera mount framer used to photograph every monitoring station on the
wavebreak structure at the Bonner Bridge Seagrass Mitigation Site 22
15 Transplanted seagrass with clean blades appearing similar to surrounding natural
seagrass at the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey 24
16 Natural seagrass blades covered with a layer of epiphytes at the Bonner Bridge
Seagrass Mitigation Site during the January 2017 survey 24
17 Workers temporarily relocating the pressure sensor at sampling locations within the
Bonner Bridge Seagrass Mitigation Site 31
18 Stationary pressure sensor installed on the seafloor at the Bonner Bridge Seagrass
Mitigation Site during the January 2017 survey 31
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 V

List of Photos
(Continued)
Photo Page
19 Representative of rock substrate for a high elevation monitoring station (Tag 35) on
the structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey 33
20 Representative photo of concrete substrate for a high elevation monitoring station
(Tag 35) on the structure at the Bonner Bridge Seagrass Mitigation Site during the
January 2017 survey 33
21 Representative photo of rock substrate for a middle elevation monitoring station
(Tag 55) monitoring two smaller rocks on the structure at the Bonner Bridge
Seagrass Mitigation Site during the January 2017 survey 34
22 Representative photo of concrete substrate for a middle elevation monitoring
station (Tag 55) showing partially wet concrete on the structure at the Bonner
Bridge Seagrass Mitigation Site during the January 2017 survey 34
23 Representative photo of rock substrate for a low elevation monitoring station (Tag
20) on the structure at the Bonner Bridge Seagrass Mitigation Site during the
January 2017 survey 35
24 Representative photo of concrete substrate for a low elevation monitoring station
(Tag 20) on the structure at the Bonner Bridge Seagrass Mitigation Site during the
January 2017 survey 35
25 North-oriented view of the wavebreak structure installed in January 2017 at the
Bonner Bridge Seagrass Mitigation Site 36
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 vi

1.0 Introduction
The North Carolina Department of Transportation (NCDOT) contracted CSA Ocean Sciences Inc. (CSA) in
2012 (Contract No. 6300032017)to conduct in-kind seagrass (mixed Halodule wrightii, Ruppia maritima,
Zostera marina) mitigation of 1.28 acres (0.52 hectares) to compensate for losses anticipated to occur
during the replacement of the Herbert C. Bonner Bridge over Oregon Inlet, North Carolina (Photo 1). The
Bonner Bridge provides the only highway connection for Hatteras Island to the mainland in Dare County,
North Carolina and its replacement is currently under construction. Based on previous published
research in North Carolina (Fonseca et al., 1998, Fonseca et al., 2000, Kelly et al., 2001, Fonseca et al.,
2002) CSA conceptualized creating a wavebreak structure to modify existing, patchy seagrass habitat by
attenuating wave activity to promote more continuous, persistent seagrass coverage.This subsequent
increase in seagrass acreage was expected to meet NCDOT's seagrass mitigation requirements while
enhancing ecosystem services for the area.
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Photo 1. Aerial image of Bonner Bridge. Source: http://www.kdhnc.com/667/Herbert-C-Bonner-
Bridge-Replacement-Project.
After installation of the wavebreak structure, CSA conducted the baseline monitoring survey in
January 2017. Baseline monitoring tasks included revisiting all bioturbation mesh experiments, installing
epibiota monitoring stations on the wavebreak structure, installing wave sensors, and collecting baseline
seagrass cover data across the entire mitigation site.This report summarizes baseline data from the
May and June 2016 and January 2017 activities and surveys.Table 1 describes CSA's previous activities
and future scheduled surveys.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01

Table 1. Activity and monitoring survey schedule for the Bonner Bridge Seagrass Mitigation Site.
Construction refers to the installation of the wave break structure.
Task Date Status
Pre-construction
Site Selection Survey April 2015 Complete
Seagrass Transplantation and Bioturbation
May 2016 Complete
Experiment Initiation
Sediment Digital Elevation Survey(USV) June 2016 Complete
Construction
Wavebreak Structure Installation 18 November 2016 to 18 Complete
January 2017
Post-construction
Baseline Monitoring Survey January 2017 Complete
Biannual Monitoring Survey August 2017 Scheduled
Biannual Monitoring Surveys May and September 2018 Scheduled
Biannual Monitoring Surveys May and September 2019 Scheduled
Annual Monitoring Survey July 2020 Scheduled
Annual Monitoring Survey July 2021 Scheduled
USV=unmanned surface vehicle.
2.0 Actions and Methods
Sections of this report that refer to construction and engineering activities or permits where originally
developed using English units, will follow the convention of reporting first in English units and then
parenthetically in metric units. For the sections of the report not directly associated with structural
engineering,the convention of reporting will be metric units following by English units parenthetically.
CSA's methods followed the accepted monitoring plan (STIP B-2500 Bonner Bridge Phase I seagrass
Mitigation Plan, Pamlico Sound, Dare, County, North Carolina; September 2015) referenced in the
permit(Permit Modification No. 106-12) to ensure all monitoring requirements were met. Surveys were
conducted prior to (in 2016) and immediately following construction of the wavebreak structure
(in 2017).
PROJECT SITE SELECTION
In 2015, CSA completed the process of site selection (Table 1). Existing seagrass cover and site
conditions were compared between potential mitigation sites within the Pamlico Sound in the vicinity
(—8 km ["j 5 mi]) of the Oregon Inlet.The Bonner Bridge Seagrass Mitigation Site was identified on a
historically stable shoal, where seagrass growth was evident, and had the most potential for increased
seagrass cover with gap closure among existing patches of the sites examined.The site was located near
dredge spoil islands approximately 4.8 km (3 mi) southwest of the existing Bonner Bridge at Oregon
Inlet. Wave and seagrass response models techniques were performed to determine the length of the
wavebreak structure forecast to achieve the 1.28 acres (0.52 hectares) of seagrass mitigation.
Also in 2015, CSA completed development of the wavebreak structure design (Section 3.0) and
placement, a task which required both wave forecasting,seagrass recovery forecasting and engineering
sub consultation for placement of the structure design.Wave forecast modeling(Malhotra and Fonseca,
2007)was utilized to estimate the wave reduction effects of the wavebreak structure. Percent wave
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 2

reduction was computed from comparisons of no-wavebreak and wavebreak modeling scenarios for
various length wavebreak structures.The percent wave energy reduction for a given length wavebreak
was converted to percent seagrass cover (recomputed from Fonseca and Bell, 1998)to predict the
overall increase in seagrass acreage across the site as the result of wave reduction. The 500-foot
(152-meter) long wall was designed with an inverted "V-shape" consisting of two 250-foot (76.2-meter)
sections.
The V-shape was a professional judgement on the part of the design team to mitigate wave impacts on
the wall from the forecast direction of maximum wave height development (northerly).Thus,the
wavebreak structure was oriented on the site to attenuate the dominant north and northeasterly
exceedance event (wind events composing the local top 5%of all hourly wind speeds, along with their
direction, over the preceding three years period) winds and create a calmer environment on the lee side
(south facing side) of the structure to promote seagrass patch coalescence and new, permanent
seagrass acreage.
Once the 500-foot (152-meter)wall length was selected by NCDOT(the wall length that most closely
approximated the forecast 1.28 acres [0.52 hectares] of new seagrass cover),four wave energy regimes
(treatments)were defined from a cumulative frequency analysis of the area covered by the modeling
effort where greater than 5%energy reduction was forecast to occur as the result of the wavebreak
structure (Figure 1). The wave energy regimes represent high wave energy reduction (>66%forecast
reduction), moderate reduction (34 to 66%), low reduction (5 to 33%), and ambient or reference
(<5% reduction).These wave energy reduction regimes became strata for random selection of various
sampling described below.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 3

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Figure 1. Post-construction forecast of wave energy (RWE; representative wave energy [J m-1 wave
crest]) based on 500-foot (152-meter) wavebreak structure, superimposed on image of
seagrass cover.This simulation is for forecast changes of a minimum of 5% in RWE between
the two scenarios of with and without the wall present.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 4

PROJECT ENGINEERING AND DESIGN
CSA subcontracted SEPI Engineering to design the wavebreak structure and provide the engineering
Signed and Sealed Design Plans.The wavebreak structure was designed based on wave height forecasts
provided by CSA using the WEMo model (Malhotra and Fonseca, 2007) and the aforementioned
exceedance event winds. To meet the 500-foot (152-meter) design length, the structure was composed
of 101 individual "Reefmaker" units each containing a central piling, one concrete base unit, and three
concrete wave attenuator units stacked on the base unit and each embedded with natural granite rock
to increase surface area for epibiota colonization (each unit was 4.8 ft x 4.8 ft x 4 ft [1.46 m x 1.46 m
x 1.22 m]) (Photos 2 and 3). Granite rock was chosen to prevent bioerosion of the enhanced surface
area. Each Reefmaker unit had a bottom clamp and a top collar installed to secure the concrete layers to
the central piling to hold the base and wave attenuator units in a fixed vertical position on the piling,
preventing settling into the sand substrate over time.
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Photo 2. East-facing view of installation of the central pilings with piling clamps at the Bonner Bridge
Seagrass Mitigation Site. Yellow arrow points to an installed clamp.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 5

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Photo 3. One Reefmaker unit consisting of one base unit on the bottom and three wave attenuator
units containing granite rock. One hundred and one of these units were installed at the
Bonner Bridge Seagrass Mitigation Site. For scale, the width of the units is 4.8 ft (1.46 m).
PRE-CONSTRUCTION SITE PREPARATION
Seagrass Relocation
In 2016, prior to installation of the wavebreak structure,the State of North Carolina Department of
Environmental Quality and Coastal Resources Commission permit (Permit Modification No. 106-12)
required any seagrass within the structure footprint and the construction corridor to be moved to the
lee side of the structure onsite. In May 2016, CSA transplanted seagrass from these areas to the lee side
of the structure (Table 1).
To assess the amount of seagrass for relocation,the structure footprint and adjacent construction
corridor was staked out to visually discern boundaries. A point-intercept survey was conducted within
the footprint and within the construction corridor(a 25-foot [7.6-meter] wide buffer area located along
the northern edge of the structure footprint) (Figure 2).Three parallel lines running the entire length of
the structure and corridor were surveyed by this method and the percent cover of seagrass computed to
determine the amount of seagrass that was to be relocated.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 6

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Figure 2. Aerial image of the wavebreak structure area at the Bonner Bridge Seagrass Mitigation Site, showing the position of the seagrass
planting areas, the construction corridor and the structure itself. Randomly selected seagrass survey points are shown for surveys
within the planted areas and nearby reference locations.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 7

Seagrass patches within the structure footprint and construction corridor were relocated to two planting
areas on the lee side of the wavebreak structure in May 2016 (Figure 2).Two scientists identified
seagrass patches to be relocated and via the sod method (seagrass and sediment; Fonseca et al., 1998).
One scientist removed sods using a square point shovel (blade dimensions 29 cm x 24 cm [11.5 in
x 9.5 in] (Photo 4) and the second scientist carefully removed the sod from the shovel blade and placed
the sod in a floating container(large plastic concrete mixing tub with flotation collar) lined with a wet
towel.The size of the sod varied (ranging from approximately 13 to 23 cm [5 to 9 in] wide and long)
depending on the density of seagrass present.Typically, larger sods were obtainable from patches with
a higher seagrass shoot density. Approximately 6 to 10 sods were the maximum limit to keep the
container afloat (Photo 5). All sods were covered with a second wet towel to keep the plants shaded
and prevent desiccation during their collection and transit to the nearby relocation site. A small number
of seagrass patches had shoot densities that were too sparse to allow removal of intact sods.Those
seagrass shoots were transplanted using the bare root technique (Fonseca et al., 1998).This technique
involved harvesting only the plant without any sediment and placing them within the floating containers
with the methods described above.The covered seagrass sods or individual shoots were typically in the
container for 15 minutes until they were planted at the relocation site.This was a very short duration for
this transplanting method and well within the tolerance limits of these seagrass species during
transplantation (pers. obs.).
The corners of the relocation areas were marked with PVC pipes and the positions recorded with the
sub-meter accuracy Trimble GeoXH handheld global positioning system (Trimble GPS).The containers
were floated to the relocation areas where a second pair of scientists planted the seagrass. One scientist
dug a sod-sized hole with a small pointed shovel and received a sod from the second scientist from the
container.The sod was placed in the hole to the level of the surrounding seafloor as found at the
harvesting location (Photo 6). Sods were planted immediately adjacent to one another within the
planting areas to form a continuous cover planting area.
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Photo 4. Underwater photograph showing harvesting of a Zostera marina-dominated seagrass sod
from within the structure footprint at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 8

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Photo 5. Image showing placement of a sod in the container for transportation to the adjacent
relocation site at the Bonner Bridge Seagrass Mitigation Site.
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Photo 6. Underwater photograph of a planted seagrass sod within the designated relocation site at
the Bonner Bridge Seagrass Mitigation Site moments after installation.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 9

Percent cover of seagrass within planted areas was evaluated immediately after transplanting and again
during the baseline survey. Each time, scientists navigated to 10 pre-selected locations (proportionally
assigned to seven locations in the larger eastern planting area and three in the smaller western planting
area) within the total planting area using the Trimble GPS. Planting area size was the result of proximity
to the extant distribution of seagrass to be relocated.
To compare the colonization of the planted areas to the surrounding natural areas, five additional
random locations were selected in the surrounding natural areas (reference area) within a 50-meter
(164-foot) distance of the planting areas (Figure 2). At each location, a 1-m2 (11-ft2) quadrat was
centered over each point and percent cover of seagrass was assessed using a modified Braun-Blanquet
(BB) cover and abundance technique (Braun-Blanquet, 1972; Kenworthy and Schwarzchild, 1997;
Fourqurean et al., 2001). Within the quadrat a BB scale value (Table 2) was independently evaluated for
percent cover of each seagrass species as well as total seagrass. Average BB scores were then converted
to percent cover for each area to allow interpolation of averaged BB scores that fall between BB scale
values (conversion is conducted by regressing the mid-point of percent cover associated within the
range covered by each BB scale value, on the associated BB scale value: Percent Cover=
2.8108*[BB]2.2325).
Table 2. Braun-Blanquet scale (score) and percent cover scale values (Braun-Blanquet, 1972).
Braun-Blanquet Scale(Score) Percent Cover(%)
0.0 Not present
0.1 Solitary specimen
0.5 Few with small cover
1 Numerous, but<5
2 5 to 25
3 25 to 50
4 50 to 75
5 75 to 100
Seagrass Cover
Seagrass cover was determined by classifying areas of seagrass occurring within the Bonner Bridge
Seagrass Mitigation Site based on aerial imagery.A georeferenced, high-resolution mosaicked aerial
image (collected by NCDOT on 24 March 2017) was used to classify areas of seagrass.The aerial image
was color-infrared (CIR) with a resolution of 0.08 m (0.25 ft). The image was subdivided into separate
classification areas of interest (AOI) based on similar pixel spectral signature ranges. Separate
classification of each AOI helped to eliminate variations in reflectance and environmental conditions
across the entire project area in order to reduce classification confusion. An unsupervised classification
was then performed on each classification A01 using a combination of iso cluster and maximum
likelihood techniques using ESRI ArcGIS 10.4 software. After running the unsupervised classifications,
each AOI was manually interpreted by denoting visually apparent classes of seagrass and classes of
non-seagrass. Spectral noise and holes within the classification results were removed and corrected
using a combination of majority filter, region group, set null (enhanced boundary edges and removed
groups of small non-contiguous pixels that were smaller than a specified value), and eliminate polygon
part (eliminated areas that were less than a specified value) tools in ArcGIS. Lastly, a manual
classification technique was then applied to the classification with guidance from a GIS analyst.This
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 10

consisted of removing areas of over-classification and adding-in (digitizing) areas where under-
classification occurred, again based on visually apparent seagrass cover.
Bioturbation Experiment
To evaluate the influence of biological disturbance on seagrass patches at the site (sensu Townsend and
Fonseca, 1998), CSA installed a bioturbation exclusion experiment in May 2016.There, 40 locations were
randomly selected from within strata (10 per strata) defined by the forecasted wave reduction pattern
following wavebreak placement(high wave energy reduction =>66%; moderate reduction = 34 to 66%,
low reduction =5 to 33%, and ambient or reference =<5% reduction) (Figure 3).The nearest isolated
seagrass patch to that location was then selected for application of the experimental treatment. At the
center of all 40 patches, a 2.4-meter(8-foot) long stainless steel rod (Photo 7) was driven into the
sediment until only 3 to 10 cm (1 to 4 in) remained above the sediment. Five randomly selected patches
were assigned wire mesh (wire remesh panels 1.07 m x 2.13 m [42 in x 84 in]) welded steel wire remesh
sheet (with 0.106 m x 0.1.06 m [4 in x 4 in] mesh size) to exclude bioturbating sting rays and five were
un-protected within each of the four wave energy regimes (total of 40 patches). At each of two
randomly selected cardinal directions per patch,the distance from the center rod to the edge of the
seagrass was measured in centimeters using a metric tape (Photo 8). For patches receiving mesh, each
of the cardinal directions received a wire mesh. The longest length of the mesh was positioned parallel
to the patch edge approximately 1/3 on seagrass and 2/3 on sand to allow room for seagrass growth
(Photo 9).Two 1-shaped rebar stakes 0.3 m (1 ft) long anchored the mesh so it was flush on the seafloor.
Flush deployment on the seafloor and anchoring were performed to prevent entanglement by sea life,
such as diving birds. Other information recorded for each patch included the treatment received
(mesh or no mesh), elevation of the rod above the sediment, and seagrass species observed at each
edge. Change in the distance from the center rod to the patch margin will be recorded over time.The
statistical approach for this experiment is a repeated measures two-way analysis of variance with wave
energy and patch protection as main effects.The mesh and stakes will be removed and disposed of
appropriately when patch coalescence begins, at which time monitoring of these patches will cease.
During the January 2017 survey, scientists revisited each patch to collect data. Scientists navigated to
the location of the center rod using the Trimble GPS. Once on location, they searched for the center rod
using a glass bottom bucket and grazing a rake (tines up) on the seafloor.The distance from the center
rod to the edge of the seagrass patch was re-measured along the same cardinal directions established
during installation. The presence or absence of mesh, elevation of the rod above the sediment, and
seagrass species observed at each edge was also noted for each patch.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 11

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Photo 7. Center rods (2.4 m [8 ft]) installed at each bioturbation experiment patch within the Bonner
Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 12

75°35'28'W 75'3520'W 75°35'17W 75'35'4'W
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75'35'20'W ?5'35'17W 35'4-1.N
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Figure 3. Randomized distribution of the seagrass patches and the experimental treatments selected
for use in the bioturbation study. This simulation is for forecast changes of a minimum of
10% in RWE between the two scenarios of with and without the wall present
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 13

I
y �s,
Photo 8. Scientists measuring from the center rod to the edge of the seagrass patch on the randomly
selected direction at the Bonner Bridge Seagrass Mitigation Site.
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Photo 9. Exclusion mesh installed flush on the seafloor on the edge of the seagrass patch within the
Bonner Bridge Seagrass Mitigation Site. Mesh size is 0.106 m x 0.1.06 m (4 in x 4 in).
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 14

Sediment Elevation
Sediment elevation was documented with two methods. One method was by direct measurement of the
height of the center rod above the sediment at each of the 40 bioturbation patches. At the center rod of
all 40 seagrass patches, the rod height above the sediment was measured used a meter stick fastened to
a piece of wood (24 cm x 5 cm x 5 cm [18 in x 2 in x 2 in]). The 0-mark on the meter stick was attached
to the center of the wood piece creating an inverted "T" shape (Photo 10). The wood was laid flush
against the seafloor to provide more surface area to avoid the ruler sinking into the substrate.The
meter stick was placed next to the rod to obtain the measurement of the rod height above the
substrate. In addition to the 40 center rods, four additional sediment rods(one per wave energy regime)
were installed in sandy substrate and rod height above the substrate was measured for each.
A second method was employed to evaluate the entire area forecast to be affected by the wavebreak. In
June 2016, CSA used an Unmanned Surface Vehicle (USV)to develop a sediment digital elevation model
to document changes in shoal elevation associated with the wavebreak structure installation. The USV
(Photo 11)was pre-programmed to run a pre-selected geographic grid at 50-m (164-ft) spacing which
encompassed the entire site. Bathymetry data was collected using duel frequency, single beam sonar at
a rate of 220 to 224 kHz. A Trimble RTK system (RTK)was mounted on the USV to integrate real time
navigation while the USV ran the pre-programmed grid lines (speed of approximately 9 kph [5.7 mph]).
The RTK had a horizontal and vertical accuracy of 2 cm (±0.787 in) and real-time tidal corrections were
applied to accurately determine water levels across the site.
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0
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Photo 10. Inverted "T" shape ruler used to measure rod height above the substrate at the Bonner
Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 15

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Photo 11. Unmanned surface vehicle (USV) collecting bathymetry data across the Bonner Bridge
Seagrass Mitigation Site.
Wave Regime and Model Validation
Long-term wave energy regime monitoring stations were placed at the Bonner Bridge Seagrass
Mitigation Site using pressure sensor loggers to record wave characteristics. Two pressure sensors
(RBRvirtuoso models) were deployed at stationary locations 25 m (82 ft) in front (north) of and behind
(south)the wavebreak structure (Figure 4). Pressure sensors were cylindrical and approximately 5 cm
(2 in) in diameter by 25 cm (10 in) long and were mounted in a locked casing horizontally on the seafloor
approximately 15 cm (6 in) above the substrate on solid base, concrete-filled pillar set 0.91 m (3 ft) into
the seafloor(Photo 12). Pressure sensors were set to record bursts of pressure data every 30 minutes at
a sampling rate of 4 Hz for 128 seconds.These data will also provide water level and tide documentation
specifically for the site, and will be downloaded twice annually to evaluate the wave energy regime
impinging on the north and south faces of the wavebreak structure.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 16

.- 75'35'16"W 75'35'12'W 75°35'8'W 75'35'4'W 75'35'0'W
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Figure 4. Stationary and temporary locations of the pressure sensors at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-17-1830-2845-07-REP-02-FIN-REV01 17

NO
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Photo 12. Photograph of one of the two wave senor brackets cemented into its base, prior to
installation at the Bonner Bridge Seagrass Mitigation Site.The hinged bracket is shown being
lifted; a disposable padlock is installed through the hinged piece to keep the sensor secure.
WEMo model validation is being developed through opportunistic sampling. During times of onsite
monitoring surveys, an RBR sensor was systematically but temporarily repositioned across the site
(Figure 4)to obtain a spatial assessment of predicted (WEMo computation to follow based on water
depth and wind conditions of the survey date)versus observed wave heights from the mobile sensor.
This spatial assessment was performed in May 2016 and in January 2017 to provide a geographically
articulated assessment of wave energy distribution with regard to prevailing conditions.The pressure
sensor was set to record bursts of pressure data at a sampling rate of 4 Hz for 128 seconds during this
sampling. In May 2016 no long-term monitoring stations had been installed and an un-tasked RBR
sensor was used. During the January 2017 survey,the pressure sensor located in front (north) of the
wavebreak structure remained as the stationary control and continued to record while the back(south)
sensor was repositionedacross the site. During each survey, scientists recorded the wind speed using
hand-held anemometers as well as wind direction prior to sampling and again after sampling was
complete. Wave data from pressure sensors were downloaded into Ruskin software (V1.13.7) and
exported to Microsoft Excel for analysis. Analysis will be comprised of simple univariate statistics of wind
speed but also predicted versus observed regression to determine the likely on-site accuracy of the
WEMo-derived wave forecasts.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 18

Wavebreak Structure
Installation
CSA subcontracted Atlantic Reefmaker to fabricate the individual Reefmaker units for the wavebreak
structure and Cape Dredging to install the wavebreak structure onsite. CSA ensured the wavebreak
structure was fabricated per the Signed and Sealed Construction Plans (SEPI, 2016; CSA, 2017) and
coordinated efforts in obtaining information to meet all NCDOT's Materials and Testing (M&T)
requirements. The individual Reefmaker units were cast, embedded with granite, and shipped to Cape
Dredging's staging area in Wanchese, NC. Installation of the wavebreak structure began on
18 November 2016 and was completed on 18 January 2017 (CSA, 2017) (Table 1). SEPI Engineering
conducted onsite supervision of construction activities throughout installation of the wavebreak
structure and provided daily progress reports during days of actual construction.
Structure Epibiota Assessment
Epibiota monitoring on the wavebreak structure was initiated in January 2017 through the
establishment of randomly-placed, permanent monitoring stations (Figure 5). Digital photographs were
recorded at each station as a time-zero (uncolonized) baseline against which subsequent epibiota
colonization will be compared for each survey time. Stations were stratified by the sides of the
wavebreak structure (30 on the exposed side [north] and 30 on the sheltered [south] side) at different
vertical elevations related to the individual wave attenuator unit placement(high, middle, and low).Ten
replicate stations were randomly assigned per elevation on either side of the wavebreak structure for a
total of 60 monitoring stations. Random locations were selected along the wavebreak structure and a
vertical elevation was randomly assigned to each location. Scientists used the Trimble GPS to navigate to
the pre-selected random monitoring station/elevation replicate along the wavebreak structure.
Monitoring stations were separated by a minimum of one Reefmaker unit.The exact horizontal location
of the monitoring station on a wave attenuator unit was visually determined where rock placement was
closest to the edge of the concrete, making them easier to photograph. Some wave attenuator units had
smaller rock embedded in the concrete, so often two small rocks were selected for monitoring. To
identify the precise monitoring location and allow precise alignment for subsequent photographs, a
numbered tag was installed on the rock immediately to the right of the selected rock(s)to be monitored
(Photo 13) and alignment points marked on the concrete surface.
A digital Sony A5000 camera in an underwater housing was installed on a PVC camera mount framer to
photograph the concrete and rock(s)at each monitoring station.The PVC frame (Photo 14) was included
in every photo to ensure standardization of photo size (dimension of the frame was 20.3 cm x 30.5 cm
[8 in x 12 in]).The camera housing was fixed to the framer with a distance of 25.7 cm (10 in) from the
housing lens to the outer edge of the frame.
To photograph the concrete portion of the wave attenuator units,the entire framer was placed flush
with the side of the concrete so the bottom edge of the concrete was included within the frame. To
photograph the rock(s), the bottom of the framer was placed flush with the top edge of the concrete
layer(where the selected rock was embedded) and the top of the framer rested on the concrete layer
located above the selected rock(s) (approximately 152 angle). One photo of the concrete and one photo
of the rock(s) were collected for all 60 monitoring stations resulting in 120 digital images. Digital images
were processed and analyzed using Coral Point Count with Microsoft Excel extensions (CPCe)V4.1
software analysis program (Kohler and Gill, 2006).The total area of evaluated rock and concrete was
calculated. CPCe utilizes the random point count method described by Bohnsack(1979) to accurately
estimate percent cover of benthic organisms and substrate from digital images.Ten random points were
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 19

projected on each image, and the biota or substrate located beneath each point was identified to the
lowest possible taxonomic level (for the time-zero images, no biota were detected). Data from each
image were assembled in a spreadsheet for percent cover calculations and subsequent comparative
analysis.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 20

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Figure 5. Epibiota monitoring stations on the wavebreak structure at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-17-1830-2845-07-REP-02-FIN-REVO1 21

A
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Photo 13. Numbered tag installed at every monitoring station on the wavebreak structure at the
Bonner Bridge Seagrass Mitigation Site.
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Photo 14. PVC camera mount framer used to photograph every monitoring station on the wavebreak
structure at the Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 22

3.0 Results
During visits to the site, scientists observed that the Bonner Bridge Seagrass Mitigation Site was
composed of patchy seagrass habitat consisting of multiple species including Zostera marina,
Halodule wrightii, and Ruppia maritima. Very fine sand (visual observation) sediments were the
dominant substrate type observed. Limited vessel traffic was observed during onsite surveys within the
immediate vicinity although commercial crabbing vessels were observed crossing the general shoal area.
Site conditions varied during each survey and were largely driven by direction and strength of the wind.
Strong northeasterly winds on site resulted in lowered water level at the site and strong southwesterly
winds resulted in higher water levels. Weather conditions during the surveys ranged from a high
temperature of 75°F (May 2016)to a low temperature of 39°F (January 2017) with wind speeds ranging
from 8 to 48 kph (5-30 mph)from various directions.
SEAGRASS RELOCATION
Seagrass patches within the structure footprint and construction corridor were relocated to two planting
areas on the lee side of the wavebreak structure (Figure 2). In May 2016, immediately after relocation,
the percent cover of seagrass was evaluated within the relocation areas and within the surrounding
reference area. Upon completion of relocation, percent cover of seagrass was 32.7%for the relocation
areas and 49.1%for the reference area (BB scores of 3.0 and 3.6, respectively) (Table 2). Transplanted
seagrass within the relocation areas appeared similar to the surrounding natural seagrass and the
borders of the planting areas were visibly indistinguishable (Photo 15). All seagrass blades were bright
green and visibly clear of epiphytic growth.
In January 2017, immediately post-construction of the wavebreak structure,the percent cover of
seagrass within the planting areas were evaluated again.The planting areas had a percent cover of 0.2%
and the reference areas had a percent cover of 7% (BB scores of 0.2 and 1.5, respectively) (Table 3). In
January 2017, a brown epiphytic layer covered the majority of the visible seagrass blades and small tufts
of brown macroalgae were observed colonizing the substrate often mixed in with seagrass (Photo 16).
Seagrass cover declined by 32.5%in the planting areas and 42.1% in the reference areas, indicating a
substantial overall drop in coverage.
Table 3. BB scores and associating percent cover for seagrass within the planting and reference areas.
Planting Area Reference Area
Survey
Total Seagrass BB Percent Cover Total Seagrass BB Percent Cover
May 2016 3.0 32.7 3.6 49.1
January 2017 0.2 0.2 1.5 7.0
Difference -2.8 -32.5 -2.1 -42.1
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 23

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Photo 15. Transplanted seagrass with clean blades appearing similar to surrounding natural seagrass at
the Bonner Bridge Seagrass Mitigation Site during the May 2016 survey.
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Photo 16. Natural seagrass blades covered with a layer of epiphytes at the Bonner Bridge Seagrass
Mitigation Site during the January 2017 survey.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 24

There may also have been an effect of wave disturbance on the relocated seagrass. Seagrass was
relocated to gaps within the natural seagrass patches in May 2016 prior to the installation of the
wavebreak structure. Construction was originally scheduled for June 2016 but was delayed. Previous
studies have shown if seagrass is relocated to areas naturally devoid of seagrass without modifying the
existing environment, natural processes will continue to preside and the relocated seagrass should not
necessarily persist (Fonseca et al., 1998).
A major storm event, Hurricane Matthew, passed through the Pamlico Sound and surrounding areas on
8 and 9 October 2016, five months after seagrass relocation, prior to the installation of the wavebreak
structure construction. The hurricane had average wind speeds ranging from 32 to 64 kph (20 to
40 mph) with maximum wind speeds of 129 kph (80 mph) initially from the north, and then switching
direction out of the southeast as the storm passed. Severe flooding occurred along the coast with an
average rainfall of 22.1 cm (8.7 in) (http://www.weather.gov/mhx/MatthewSummary). The hurricane
occurred at the end of the 2016 seagrass growing season, so effects from the storm on seagrass cover
should still have been captured during the January 2017 survey.Therefore in addition to potential
seasonal changes, this event may also contribute to the decrease in seagrass percent cover especially in
the relocation areas observed during the January 2017 survey. It is possible that the relocated seagrass
had not fully established a sufficiently robust root and rhizome system during the five months from
relocation to the storm event, leaving them susceptible to erosion. Fonseca et al. (2000) observed that
natural patches shrink from erosion at their margins due to extreme storm events in North Carolina, but
that would not explain a decrease in cover within the confines of the reference beds. Fonseca et al.
(2007) determined that seagrass shoots can be broken by extreme events, but whether that would
result in shoot density and coverage changes was not tested. Continued examination of the planted and
reference areas during subsequent growing seasons should reveal whether the planted area was
differentially affected by this storm event.
SEAGRASS COVER
The Bonner Bridge Seagrass Mitigation Site was forecast to include 301.6 acres (122.1 hectares), and
boundaries were determined by using the wave forecast model prediction. Seagrass cover within these
boundaries was determined by classifying areas of seagrass based on aerial imagery provided by NCDOT.
Classification resulted in 33.4 acres (13.5 hectares) of seagrass cover over the 301.6 acre (122.1 hectare)
site (Figures 6 and 7).
In aquatic systems, classification methods rarely achieve 100%accuracy. This is because unlike
terrestrial systems whose classification is limited primarily by atmospheric conditions, classification of
aquatic systems, especially benthic components are limited by both atmospheric and water conditions.
Thus, the accuracy of seagrass classification largely depends on water clarity and sea surface condition
at the time of imagery acquisition. Weather events have an effect on waves on the water surface which
actively degrade visualization of the seafloor, as well as water clarity. In addition, wind events occurring
immediately prior to imagery collection may cause latent sediment suspension that negatively impact
results. Finally, many seagrass patches were interdigitated with sand and often non-contiguous which
complicates precise delineation. In addition to atmospheric and water column effects, mosaicking of the
image produced shading gradients which interfered with seagrass classification accuracy of the seagrass
areas and appeared to be the source of most inaccuracy. An absence of ground control points taken in
association with the imagery prevented further accuracy assessment.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 25

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Figure 6. Baseline classification results identifying areas of seagrass (yellow) within the Bonner Bridge
Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 26

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Figure 7. Enlarged view of baseline aerial imagery (left) and classification results (right) identifying areas of seagrass (yellow) within the
Bonner Bridge Seagrass Mitigation Site.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 27

BIOTURBATION EXPERIMENT
At the time of setting out the experiment in May 2016, the average distance from the center rod to the
edge of all 40 patches was 3.8 m (12.5 ft) (Table 4). At the onset of the experiment patches with
exclusion mesh had an average distance of 3.9 m (12.8 ft)and patches without exclusion mesh had an
average distance of 3.7 m (12.1 ft).
Table 4. Average distances in meters from the center rod to the edge of the patch for the
bioturbation experiment.
Survey All 40 patches(m) Patches with Patches without
exclusion mesh(m) exclusion mesh (m)
May 2016 3.8 3.9 3.7
January 2017 3.5 3.7 3.3
In January 2017, all 40 bioturbation patches were revisited and monitored. For all 40 patches,the
average distance from the center rod to the edge of the patch was 3.5 m (12.5 ft) (Table 4). Only 20%of
the mesh (8 out of 40 sheets) was found during this survey. It is likely that sedimentation associated
with Hurricane Matthew may have moved or buried these mesh, or other external factors such as
vandalism may have occurred. Where exclusion mesh was found,the average distance to the edge of
the patch was 3.7 m (12.1 ft). Patches without exclusion mesh had an average distance of 3.3 m (10.8
ft). When examining change in distance from rod to patch edge, by treatment and wave energy strata,
no coherent pattern emerged and no statistically significant difference (two-way ANOVA; p <0.05)was
detected among treatments (no significant interaction among wave strata and mesh treatment and no
significant differences in the distance from the rod to the edge either among wave strata or among
treatments (mesh, no mesh).
SEDIMENT ELEVATION
Sediment elevation was monitored across the entire site by measuring the center rods at all
40 bioturbation patches and four additional sediment rods placed in sandy substrate. A total of
40 center rods were installed in May 2016 and the average rod height above the sediment was 6.8 cm
(2.7 in).The average height of the four sediment rods above the sediment was 6.9 cm (2.7 in). In January
2017, a total of 32 center rods were located and the average rod height was 11 cm (4 in).Two of the
four sediment rods were located and the average rod height was 12.4 cm (4.9 in).The eight center rods
not located may be deeply buried and future attempts will be made to locate them. If they were deeply
buried then the average rod height would decrease.
The USV collected bathymetry data across the entire site in June 2016 (Figure 8).The survey was
conducted during both flood and ebb tides and real-time tidal corrections were made to data collected.
Water depths ranged from 0.7 to 1.6 m (2.3 to 5.2 ft) across the site.The western portion of the site was
notably shallower than the eastern portion.The USV will collect bathymetry data during the final
monitoring survey and data will be compared to this baseline bathymetry.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 28

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Figure 8. Track lines traveled by the Unmanned Surface Vehicle (black lines) and digital elevation
model at the Bonner Bridge Seagrass Mitigation Site. Soundings are in MLLW.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 29

WAVE ENERGY
Before installation of the wavebreak structure, one pressure sensor was temporarily repositioned to
19 preselected locations around the site on 18 May 2016 to collect WEMo validation data (Photo 17).
Weather conditions were rainy, cloudy, and windy with average wind speeds of 29.7 kph (18.5 mph) and
maximum gusts up to 39 kph (24 mph)from the northeast. Another opportunity arose to collect a
second set of validation data immediately post-construction of the wavebreak structure. Here, one
pressure sensor was temporarily repositioned to 24 preselected locations on 15 January 2017. Weather
conditions were cloudy and windy with average wind speeds of 13 kph (8 mph) and maximum gusts up
to 19 kph (11.8 mph) from the northeast. After the wavebreak structure was installed, pressure sensors
were installed at specified stationary locations in front (north) of and behind (south) the wavebreak
structure to spatially assess wave energy distribution (Photo 18). Data collected from the pressure
sensors and wind measurements will be used to assess the accuracy of the WEMo wave forecasts;these
results will appear in a subsequent report.
Wave forecast modeling using WEMo was initially conducted in January 2016 for different lengths of the
wavebreak structure. Modeling was re-analyzed in January 2017 after installation of the 500 ft (152 m)
wavebreak(Figure 1). As done previously,the model was run on 65-foot(20-meter) grid cells, as the
bathymetric data which are an important driver of the calculations is not more resolved than that
distance.The total acreage of seafloor under influence by the various the four zones of wave reduction
is given in Table 5.
The potential generation of new seagrass cover was computed under two scenarios. One scenario
(mapped in Figure 1) was computed where the area of influence of the wall was based on a minimum of
a 5%difference in RWE with and without the wall present.The second scenario, (mapped in Figure 3)
was computed where the area of influence of the wall was based on a minimum of a 10%difference in
RWE with and without the wall present.The scenario with the 10%threshold results in a smaller area of
seafloor being affected than using only the 5%threshold.Theoretically,this could result in a total of 1.78
acres (0.72 hectares) of new seagrass overall, with the 10% reduction zone producing 1.13 acres (0.46
hectares) and the 5% reduction zone producing 1.50 acres (0.61 hectares).The accuracy of these
projections will be quantified from NCDOT-supplied aerial imagery over time.
Table 5. Representative wave energy (RWE) reduction zones depicted in Figure 1 in both acres and
square meters.
Percent RWE Reduction Zones Square Meters Acres
>66% 3,184 0.8
33%to 66% 21,153 5.2
5%to 33% 200,889 49.6
<5% 1,095,260 270.6
After the model was run and a smoothing technique (krigging) applied (Figure 1),there is the
appearance of a disruption in the wave reduction just south of the wall. However,this is a product of the
krigging and that small zone of 33-66%wave reduction just south of the wall is a display artifact and was
not part of the acreage calculations.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 30

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Photo 17. Workers temporarily relocating the pressure sensor at sampling locations within the Bonner
Bridge Seagrass Mitigation Site.
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Photo 18. Stationary pressure sensor installed on the seafloor at the Bonner Bridge Seagrass Mitigation
Site during the January 2017 survey.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 31

STRUCTURE EPIBIOTA
Time-zero epibiota growing on the wavebreak structure was evaluated by installing 60, randomly
located fixed monitoring stations on the wavebreak structure in January 2017, immediately post-
construction. Photographs of the concrete and rock(s) at each monitoring station will be used as the
baseline data set. Each consecutive monitoring survey will evaluate the exact same surface area of
concrete and rock because the monitoring stations were installed at fixed locations. The percent cover
of concrete and rock were both 100%, and is expected to decrease in future monitoring surveys as
epibiota colonize the structure.
During the January 2017 survey,the ebb tides were very low and monitoring stations at all three
elevations (high, middle, and low) were all exposed above the water level. Monitoring stations at the
higher elevation were completely dry even at flood tides(Photos 19 and 20).The middle elevation
monitoring stations were primarily dry on the rocks but the concrete on the sides were regularly
splashed by waves hitting the structure below (Photos 21 and 22).The low elevation was primarily wet
and was often submerged at flood tides or when winds increased wave activity around the structure
(Photos 23 and 24).The low elevation was often already seen with a thin layer of algae covering the
concrete and rock substrates.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 31

dinar
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Photo 19. Representative photo of rock substrate for a high elevation monitoring station (Tag 35) on
the structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017 survey.
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Photo 20. Representative photo of concrete substrate for a high elevation monitoring station (Tag 35)
on the structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 33

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Photo 21. Representative photo of rock substrate for a middle elevation monitoring station (Tag 55)
monitoring two smaller rocks on the structure at the Bonner Bridge Seagrass Mitigation Site
during the January 2017 survey.
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'
I
Photo 22. Representative photo of concrete substrate for a middle elevation monitoring station
(Tag 55) showing partially wet concrete on the structure at the Bonner Bridge Seagrass
Mitigation Site during the January 2017 survey.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 34

•
te
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Photo 23. Representative photo of rock substrate for a low elevation monitoring station (Tag 20)on the
structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017 survey.
,., p ,1?
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.... i. ,:.. . . , ...... ..4:._,.. ,:,z,,,,e ,.,...A ../..;`, •
f 1 , ...c CG ,;.'{f' y'.'- T ,,t H. I • fT~.. ';(:'fr^ .
} `
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Photo 24. Representative photo of concrete substrate for a low elevation monitoring station (Tag 20)
on the structure at the Bonner Bridge Seagrass Mitigation Site during the January 2017
survey.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REV01 35

4.0 Conclusions
The wavebreak structure has been successfully installed as of January 2017 (Photo 25) and passed its
post-construction engineering inspection. Monitoring will continue for an additional four years (Table 1)
which will build off of this post-installation report.
Photo 25. North-oriented view of the wavebreak structure installed in January 2017 at the Bonner
Bridge Seagrass Mitigation Site. The total structure length is 500 ft (152 m).
Seagrasses were successfully relocated from the construction corridor to two planting areas south of the
wall footprint in May 2016. Seagrasses in the area are composed of all three of the marine species found
in North Carolina (mixed Halodule wrightii, Ruppia maritima,Zostera marina). Seagrass cover measured
within the confines of natural, colonized seagrass displayed dramatic change from May 2016 to January
2017 (-42%).The planted areas showed a similar decline of-35.0%. It cannot yet be determined if this
change is a typical seasonal change in cover (spring versus winter) or if there was a contribution from
Hurricane Matthew.The hurricane passed over this area on 9 October 2016, prior to the installation of
the wavebreak structure; thus,the planted areas were highly exposed to an extreme wave event only
5 months post-relocation which could have led to disruption of the transplanted seagrasses.
A bioturbation experiment to help determine the relative role of bioturbation versus wave energy
reduction in seagrass space occupation was significantly disrupted by unknown sources. Only 20%of the
mesh (8 out of 40 remesh sheets) was found during the January 2017 survey.The wavebreak was not
present during this time so comparisons could only be tested among the remaining 8 remesh sheets and
those edges that did not receive remesh. There was no significant difference (p<0.05) among the
change in distance between the remesh and no remesh treatments, preliminarily indicating that
bioturbation was not strongly influencing the expansion of patch margins at that time. However,the
passage of Hurricane Matthew may have obscured effects (disturbance effects like Hurricane Matthew
erode seagrass patches from their edge, much like sting ray bioturbation; Fonseca et al., 2000).
Physical data collection of sediment elevation and wave energy has been completed. A digital elevation
model of the site was collected using the USV and these data will be compared with an end-of-project
survey conducted in the same manner to determine net sediment accumulation or loss in the project
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 36

area. Sediment elevation stakes will also continue be monitored to gain an understanding of shorter
term fluctuations in sediment elevation.An overall change in sediment elevation (-4.1 cm) was detected
which cannot be attributed to the wavebreak structure as similar differences occurred across the entire
shoal.
The final wave modeling effort indicated that theoretically,the wavebreak influence on seagrass cover
could result in a total of 1.78 acres (0.72 hectares) of new seagrass overall, with the 10% reduction zone
producing 1.13 acres (0.46 hectares) and the 5% percent reduction zone producing 1.50 acres
(0.61 hectares).The classification resulted in 33.4 acres (13.5 hectares) seagrass cover across the Bonner
Bridge Seagrass Mitigation Site.Aerial imagery will be collected and analyzed annually to capture
changes in seagrass cover associated with the addition of the wavebreak structure.
Finally,time-zero data collection for epibiotic colonization was completed using a stratified random,
repeated measures design. As expected,there was no discernible epibiotic colonization in any of the
120 digital images recorded. Photographs of the exact locations on the structures, stratified by tidal
elevation and north and south sides of the wall will be repeated over time to quantify epibiotic
colonization trajectory, abundance and composition.
5.0 References
Bohnsack,J.A. 1979. Photographic quantitative sampling of hard-bottom benthic communities. Bulletin
of Marine Science 29:242-252.
Braun-Blanquet,J. 1972. Plant sociology: the study of plant communities. Hafner.
CSA. 2017. B-2500 Bonner Bridge Seagrass Mitigation Site As-Built Report. CSA-NCDOT-FL-17-183O-
2845-07-REP-0I-FIN.
Fonseca, M.S. and S.S. Bell. 1998.The influence of physical setting on seagrass landscapes near Beaufort,
NC, USA. Mar. Ecol. Prog. Ser. 171:109-121.
Fonseca, M.S.,W.J. Kenworthy, and G.W. Thayer. 1998. Guidelines for the conservation and restoration
of seagrass in the United States and adjacent waters. NOAA COP/Decision Analysis Series.
222 pp. http://docs.lib.noaa.gov/noaa_documents/NOS/NCCOS/COP/DAS/DAS_12.pdf_
Fonseca, M.S., W.J. Kenworthy, and P.E. Whitfield. 2000.Temporal dynamics of seagrass landscapes: a
preliminary comparison of chronic and extreme disturbance events. Biol. Mar. Medit. 7:373-376.
Fonseca, M.S., P.E. Whitfield, N.M. Kelly, and S.S. Bell. 2002. Modeling seagrass landscape pattern and
associated ecological attributes. Ecological Applications. 12:218-237.
Fonseca, M.S., M.A.R. Koehl, and B.S. Kopp. 2007. Biomechanical factors contributing to self-
organization in seagrass landscapes. J. Exp. Mar. Biol. Ecol. 340:227-246
Fourqurean,J.W., A.Willsie, and C.D. Rose. 2001. Spatial and temporal pattern in seagrass community
composition and productivity in south Florida. Marine Biology 138:341-354.
Kelly, N.M., M.S. Fonseca, and P.E. Whitfield. 2001. Predictive mapping for management of seagrass
beds.Aq. Cons. Mar. Fresh. Ecosys. 11:437-451.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 37

Kenworthy, W.J. and A. Schwarzchild. 1997.Vertical growth and short shoot demography in Syringodium
filiforme in outer Florida Bay, USA. Marine Ecology Progress Series 173:25-37.
Kohler, K.E. and S.M. Gill. 2006. Coral Point Count with Excel extensions(CPCe):A Visual Basic program
for the determination of coral and substrate coverage using random point count methodology.
Computers and Geosciences 32(9):1,259-1,269.
Malhotra, A. and M.S. Fonseca. 2007. WEMo (Wave Exposure Model): Formulation, Procedures and
Validation. NOAA Technical Memorandum NOS NCCOS#65. 28 pp.
http://www.ccfhr.noaa.gov/docs/NOS_NCCOS_65.pdf.
SEPI Engineering& Construction. 2016. Complete Construction Plans.
Townsend, E. and M.S. Fonseca. 1998.The influence of bioturbation on seagrass landscape
patterns. Mar. Ecol. Prog. Ser. 169:123-132.
CSA-NCDOT-FL-18-1830-2845-07-REP-02-FIN-REVO1 38