NCDOT 106-12 B-2500 Phase I As-Built Report 4/17/2017

4
Brittingham, Cathy
From: Herring, Kathy
Sent: Monday, April 17, 2017 12:52 PM
To: Brittingham, Cathy; Huggett, Doug; Staples, Shane; Daisey, Greg
Cc: Willis, Thomas C; Paugh, Leilani Y; Medellin, Danielle ([e-mail])
Subject: Wave attenuation structure as built report
Attachments: NCDOT_FL_17_1830_2845_SEPI_AsBuilt_Final.pdf
Attached you will find the as-built report for the wave attenuation structure in the Pamlico Sound. This submittal
complies with condition#13 in the B-2500 Phase I Mitigation Site CAMA Permit Major Modification 2015-12-15 (Permit
Number 106-12). Please call me if you have any questions.
Thank yowl S
Kathy IIS � � l
glactgeS
Kathy Herring
Environmental Program Supervisor
Natural Environment Section, Project Development and Environmental Analysis
North Carolina Department of Transportation
919 707 6128 office c \y
{� S�. �� �919 971 4367 mobilef•
mkherrinqncdot.gov
fic 0 oT r_nsr c..\-o S
1020 Birch Ridge Drive
1598 Mail Service Center (�
Raleigh, NC 27699-1598 C)`1y Re 0C
E.(\o,;(\__c_e c S �� sufw/Y\ cr•7
7
jii.
lice fran_S-c
r101:
Email correspondence to and from this address is subject to the S
North Carolina Public Records Law and may be disclosed to third parties. .SUC'V\v'`Q �. q— P
Facebook Twitter YouTube \,,e�U-S€
Me w ;� cIA c1
Al` ek \(� A m orc\ Vk o c T
t
Email correspondence to and from this sender is subject to the N.C.Public Records Law and may be disclosed to third parties. D ())4Y-C\--103-
,p. 3\ge7= jt( c:V-v se Oe S S jn aY\a AS\ov\ I— -5-(1 Py
r /
,3\9
1

B-2500 Bonner Bridge Seagrass Mitigation Site
As-Built Report
March 2017
_
-.. _
,4'
DANGER
I
I
aA
2.7
i _ 4
_ - _
A
Prepared by:
SEPI
Prepared for: ENGINEERING a
CONSTRUCTION
5030 New Centre Drive, Suite B
E,, j jWilmington, North Carolina 28403
r
Natural Environment Section /�'c''�
V North Carolina Department of Transportation A
CSA Ocean Sciences Inc.
8502 SW Kansas Avenue
Stuart, Florida 34997

CSA
GSA Ocean Sciences Ina.
As-Built Report
DOCUMENT NO. CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN
Version Date Description Prepared by: Reviewed by: Approved by:
01 03/01/17 Initial draft for review SEPI Engineering M. Fonseca M. Fonseca
D. Medellin
FIN 03/28/17 Final SEPI Engineering M. Fonseca M. Fonseca
D.Medellin
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
List of Tables iii
List of Figures iii
List of Photos iii
1. Background - 1
1.1 PROJECT OBJECTIVE 1
1.2 SITE SELECTION 1
2. Wavebreak Structure Design, Location and Bathymetric Support 2
3. Construction and Inspection 7
Phase 1—Reefmaker Casting 7
Phase 2—Pre-construction Site Preparation 7
Phase 3—Material Transport 7
Phase 4—Wavebreak Structure Installation 7
Phase 5—As-Built Survey Points 8
Phase 6—Post-Construction Inspection 8
4. As-Built Summary 9
5. References 9
Appendices 11
Appendix A: Detailed information for daily construction activities A-1
Appendix B: Scouring measurements at randomly located positions on both sides of the
wavebreak structure B-1
List of Tables
1 Seagrass and elevation survey results 2
2 500-foot wavebreak structure surface area calculations 6
List of Figures
1 Digital elevation model showing the water depth in meters relative to mean low,
low water and tracklines of the unmanned surface vehicle(USV) used to collect the
bathymetry data 4
2 Locations of randomly selected scouring samples 8
List of Photos
1 East-facing view of installation of the central pilings with piling clamps at the Bonner
Bridge Seagrass Mitigation Site 5
2 One Reefmaker unit consisting of one base unit on the bottom and three wave
attenuator units containing granite rock. 6
CSA-NCDOT-FL-17-1830-2845-07-REP-0I-FIN )��

1. Background
The Herbert C. Bonner Bridge provides the only highway connection for Hatteras Island to the mainland
in Dare County, North Carolina via NC 12 and US 64.The Bonner Bridge has reached the end of its
service life and will be replaced with a new bridge that will provide access to Hatteras Island across
Oregon Inlet(State Transportation Improvement Project[STIP] B-2500). In 2012, CSA Ocean Sciences
Inc. (CSA) was contracted by the North Carolina Department of Transportation (NCDOT)to conduct
seagrass mitigation to compensate for losses anticipated to occur during the replacement of the
Bonner Bridge over Oregon Inlet (Fonseca, 2015).
Submerged aquatic vegetation helps stabilize coastal shorelines through rhizome binding of
sediment in shallow nearshore regions, suspended sediment trapping, and wave and current
attenuation (Koch et al. 2006).SAV distribution is driven by water depth, light penetration, nutrient
loading,salinity, exposure to waves and currents, biological disturbance and fishing practices, and in
particular, vulnerability to extreme storm events(Thayer et al. 1984, Fonseca et al. 1998). Because
SAV have stabilizing effects on the coastlines around the areas they inhabit,substantive changes in the
SAV community will influence the physical integrity of the coastline(Fonseca 1996).In addition,because
SAV provides critically important food and shelter for fisheries,changes in SAV will affect the fisheries of
the future(Stephan et al. 1997).
Replacement of the Bonner Bridge will permanently impact approximately 2.66 acres of SAV areas
for which mitigation will be required.Mitigation measures will include removal of the existing bridge that
will unshade 1.38 acres of suitable habitat, and the remaining 1.28 acres will be mitigated near the
project area by installing a wavebreak.This wavebreak will provide habitat to generate 1.28 acres of
new SAV acreage as mitigation and is coupled with an additional 0.3 acres of hard surface habitat
suitable for colonization by algae,oysters and other sessile communities.
1.1 PROJECT OBJECTIVE
The objective of this mitigation project is to reduce the amount of wave energy within the project site to
allow for a more continuous cover of SAV (specifically the seagrasses Halodule wrightii and
Zostera marina and opportunistically Ruppia maritima)to expand,providing increased seagrass acreage
and associated ecosystem services. These services include water quality improvement, aquatic habitat
creation, reduced sediment movement and plant community establishment.The constructed
wavebreak structure will also create new linkages between intertidal and aquatic environments.
1.2 SITE SELECTION
The mitigation site(Site S2)is located immediately west of the existing Bonner Bridge(Appendix A),and
was selected as the preferred site following an April 28, 2015 field verification by CSA. It is located on a
stable shoal that has supported patchy seagrass cover since at least 1998. During this field visit, a
point-intercept survey was conducted at several candidate sites 52, S2A and S4 to determine the
beginning and end point of seagrass along each transect and ultimately the SAV percent cover.
Site S2 demonstrated a modest seasonal fluctuation in seagrass cover, increasing 15 percent since
the previous survey conducted in 2012, but only to 26 percent cumulative cover(Table 1). Site S2A was
rejected because of an emerging clay lens observed in the potential planting area (SAV does not grow
well in clay). Site S2 was selected over Site S4 because of the potential fora greater increase in seagrass
cover among the existing patches at 52.
CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN 1

Table 1. Seagrass and elevation survey results.
Site Percent Cover Percent Cover Averag2015ch Size Seafloor Elevation
(2015) (2012) ( ) (ht. above MSL in ft)
(ft2)
Site S2 26 11 26.9 -1.48
Site S2A 3 7 31.2 -2.66
Site S4 54 53 84.6 -2.89
The proposed site was staked and signed to demarcate the wavebreak structure location by a licensed
surveyor during the public notice period;additional signage was posted at Oregon Inlet Fishing Center.
2. Wavebreak Structure Design, Location and Bathymetric Support
CSA completed development of the wavebreak structure design and placement,a task which required
both wave forecasting, seagrass recovery forecasting and engineering sub consultation for placement of
the wavebreak structure.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 modeling scenarios with and without the wavebreak structure for various lengths.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.
In order to perform the wave forecast modeling, additional bathymetric data were needed. Bathymetry
data for the Oregon Inlet area were examined using the National Oceanic and Atmospheric
Administration (NOAA)coastal relief model, Geophysical Data System (GEODAS),and locally available
Light Detection and Ranging(LIDAR)data. However,the coverage for these various sources revealed
substantial spatial gaps and deficiencies (e.g., missing dredge islands, poor depth agreement with
on-site,tidally corrected observations and these digital sources), especially in proximity to seagrass
habitats of interest within the required 5 mile search area.Therefore, during an October 2012 site visit,
CSA conducted a bathymetry survey over both far-field (—80 km2) and near-field extents (a 1 km2 area
around all proposed sites, including the S2 site finally selected)to improve subsequent wave modeling
efforts that are highly sensitive to near-field bathymetric information. Continuous bathymetry data were
collected for the far-field survey lines at 300-m spacing.The 1 km2 areas were at 50-m spacing.The
survey area covered —80 km2and—300 km of survey lines.
To correct the survey for tidal stage,a pressure sensor was installed adjacent to the Center for
Operation Oceanographic Products and Services (CO-OPS)tide station at the Oregon Inlet Marina
(Station 8652587)to provide real-time water level information for correction of the bathymetry surveys.
The tide gauge elevation was recorded using a Trimble GeoXH GPS in reference to local NOAA elevation
benchmarks (relative elevation of benchmark derived from 20 minute on-station collection).
Survey operations were conducted from an 8-m (26-ft)vessel with an enclosed pilot house, which
contained all supporting electronics and computer systems. HYPACK navigation software interfaced with
an on-board Trimble AG-106 differential global positioning system to navigate the vessel. HYPACK also
provided real-time display of the vessel's track along the pre-plotted survey lines and logged all
positional and bathymetric data. Bathymetry data were collected throughout the survey using a
CSA-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 2

SonarMite MILSpec Echo Sounder with a 200 kHz transducer capable of 1-cm accuracy.All survey data
was processed and adjusted for tidal corrections and were used as the basis for the wave forecast
modeling.
The 500-foot length for the wavebreak structure was selected by NCDOT as the minimum length that
most closely approximated the forecast 1.28 acres of new seagrass cover.The 500-foot wavebreak
structure was designed with an inverted "V-shape" consisting of two 250 ft sections.The V-shape was a
professional judgement on the part of the design team to mitigate wave impacts on the wavebreak
structure from the forecast direction of maximum wave height development(northerly).Thus,the
wavebreak structure was oriented on the north side of the S2 site to attenuate the dominant north and
northeasterly exceedance wind events and create a calmer environment on the lee side (south side)to
promote seagrass growth.The precise location of the structure is described in the survey report in
Appendix A.
An additional,yet more highly resolved bathymetric survey was conducted in the immediate vicinity of
the wavebreak structure to create a digital elevation model (DEM)of the sediment surface. For
repeatability,this survey was performed using CSA's Unmanned Surface Vehicle(USV) equipped with a
real-time kinematic(RTK) Geographic Positioning System(GPS;Trimble SPS461) linked to an associated
base station that was calibrated to the NCDOT Bonner Bridge monument elevation datum (NAVD88
corrected to MLLW).The USV was programmed to sail a grid (Figure 1)on 50 m centers across the entire
forecasted wave shadow of the wavebreak structure.The USV continually collected bathymetric data
with an ODOM Hydrographics 300CSV fathometer with a dual frequency(200/24 kHz)transducer. All
positional data were corrected for roll, pitch and yaw using a Trimble R8 RTK System Controller yielding
+/-3cm (0.98 ft) horizontal and 9.1 cm (0.29 ft)vertical resolution.. These data will be compared to a
final DEM survey at the end of the monitoring period. Pre-construction water depths on the mitigation
site ranged from 0.7 to 1.6 m (2.3 to 5.2 ft)and were typically shallower on the west side of the site
(Figure 1).The placement of the wavebreak structure was approximately 275 m (900 ft) east of the
closest existing navigation channel. Given this distance and the observed stability of the shoal over
time (Google Earth imagery; 2004, 2006, 2008,2009,2011,2014 and recent NCDOT high resolution
imagery 2012,2015),this distance was judged to be adequate to avoid any influence of the channel
•
CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN 3

753530'W 753,520'W 75.3510'W 75•350'W
I'
c r 1 L... . ..
1. __ .. i .1 A
A 7 a
A
w+>
'111 ...- arie00.1.81441•46:_ _ . .
i "��t z a _:1t
b
vCo;Q
iii
1
sue' • _
1 Vf
t
b Z
Q 2
o
I Q
M
4 1
4
„� t ' Legend
USV Survey 7rackline
- -500ft Wavebreak Structure
Bathymetry(m)
_ L_Jo7-oa
z
8 1 io8-09 o
, - k i (.... 1E109-1
A
1-1.1
-`,-.. L - ' c
) - =1.1-1.2
-1.2-1.3
-13-1.4
-1.4-1.6
75'3530"W 75°35'20"W 75`35'10"W 75.35'0"W
0 100 200 400 Meters
I t + I + I t i0
C SA Coordinate System WGS 1984 UTM Zone 18N
Depth in Meters
Figure 1. Digital elevation model showing the water depth in meters relative to mean low, low
water and tracklines of the unmanned surface vehicle (USV) used to collect the
bathymetry data.
CSA-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 4

•
The wavebreak structure design involved installing a continuous series of 101 individual units,
termed "Reefmaker units",constructed by Atlantic Reefmaker. Each Reefmaker unit contained a central
piling, one base unit, and three wave attenuator units of stacked concrete layers embedded with natural
granite rock(dimensions of each Reefmaker unit was 4.8 ft x 4.8 ft x 4 ft) (Photos 1 and 2). Each
Reefmaker unit had a bottom clamp and a top collar installed to secure the concrete layers to the
central piling. Reefmaker units were designed to fully attenuate wave energy while allowing for the
exchange of water and the passage of organisms through and around the structure's individual
components.Moreover,they were designed for use in high energy wave environments and to survive the
passage of large storms such as hurricanes.
t
r,
« .—
r . \,.'"'vim
:,.
r r O. ,,,
Photo 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-17-1830-2845-07-REP-01-FIN 5

-10.4441,
_ .� O.. .._
4, 'El
31
31 z+
% 1
L r
37 i
WM
Photo 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 horizontal distance of each layer
is 4.3 ft (1.31 m).
Additional benefits of the Reefmaker unit design for the wavebreak structure include the ability to
increase hard surface area for epibiota settlement,and have a smaller benthic footprint than traditional
wavebreak techniques.The Reefmaker units will provide considerable surface area for oyster settlement
and other epifaunal recruitment(Table 2). Based on preliminary design it is anticipated that
approximately two units will be submerged below the normal high water level. Reefmaker units have a
much smaller benthic footprint (23 ft2 per unit)than a traditional rock wavebreak to reach the desired
height. A traditional rock wavebreak of similar size with 2:1 slopes would have a 10,000 ft2 benthic
footprint.The constructed 500 ft wavebreak structure had a benthic footprint of 2,500 ft2.
Table 2. 500-foot wavebreak structure surface area calculations.
Wave Attenuator Units (vertical) Surface Area (sq.ft [ac]) Total Reefmaker Units
2 11,413 (0.26) 101
2.5 14,696 (0.34) 101
3 17,978(0.41) 101
C5A-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 6

3. Construction and Inspection
The construction of the wavebreak structure involved the following construction phases:
Phase 1—Reefmaker Casting
• Casting molds were prepared and set up for pouring at Cape Fear Precast facility located at
(620 Mildred Thomas Road Jacksonville, North Carolina, 28540)
• Concrete pouring occurred and the Reefmaker units were created
• Materials testing for strength was completed and units certified as meeting NCDOT standards prior
to shipping
• Reefmaker units, pilings and hardware were trucked to the land based staging site at(301 Harbor
Road Wanchese, North Carolina, 27981)
Phase 2—Pre-construction Site Preparation
• Seagrasses were relocated from structure footprint and the construction corridor to the lee side of
the wavebreak structure
• The exact wavebreak structure location was surveyed and staked by a certified land surveyor
• Batter boards were installed and the installation reference line was established
Phase 3—Material Transport
• Materials including pilings,Reefmaker units,and hardware were loaded onto the shallow draft barges
and transferred to the site from the land based staging area.
• During extreme low tide conditions the barge was pushed onto the site by hand to minimize bottom
impact and potential propeller scarring of seagrass
Phase 4—Wavebreak Structure Installation
Detailed information for daily construction activities are listed in Appendix A.
A 24 x 45 ft (7.3 x 13.7m)shallow draft barge with a 42 ft(12.8 m) extended reach excavator was used in
conjunction with specialized 20 cm (8 in) spuds to minimize benthic impacts. Pilings were positioned,
jetted and vibrated to depths of 6 m (20 ft)then leveled. Due to the dynamics of Oregon Inlet, potential
entanglement of aquatic species, and issues concerning worker safety,turbidity curtains were not used
during construction. In order to compensate for not using turbidity curtains,jetting time was
documented during piling installation (Appendix A). Bottom clamps were installed and torqued to
correct specification following piling installation.The Reefmaker units were individually and
systematically assembled on site, using the extended reach excavator and personnel,for positioning.
Clamps were installed following unit placement to secure the wave attenuator units to the piling. Signal
lights and warning signage were positioned and installed using specifications from the U.S. Coast Guard
Private Aids to Navigation Permit. During installation,a site supervisor under contract to CSA(SEPI)
provided daily oversight for all construction activities and ensured all construction activities remained
within the construction corridor,followed the pre-approved construction plans, and were permit
compliant(Appendix A).
CSA-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 7

Phase 5—As-Built Survey Points
• Corner points on top of Reefmaker unit(7 locations)
• Bottom of Reefmaker unit (7 locations)
• Center line of pilings (7 locations)
• Top of signal lights(3 locations)
Phase 6—Post-Construction Inspection
CSA measured the scouring on both sides of the wavebreak structure at various known locations
(Figure 2).The average distance from the seafloor to the bottom of the base unit was 30.7 cm (12.1 in)
for the entire wavebreak structure (Appendix B).The width of the scouring was approximately 0.3 m
(1 ft)out from the edge of the wavebreak structure and the elevation of the seafloor outside of this
buffer area remained unchanged.
75°3914'W 7535131W 75-35174i 75.35'11 W 75'3510'W 75.359'W 75.35.WW
.. . : gip.*- r
@ s • /' Air
d
0
9 a 4 911 9€)
z 1)3
A
l.epend
• Scouring Semple Location
500ft Vtarrebreak Structure
1=
75.3519.W 75'35.131W 75'35'12W 75.3511•W 75'3510"W 75.359'W 75'39E15/ .';R
025 5 100 Meters
P I I 1 i I t r I I0
CSACoereinate System VGS 1964 UTl Zon 16N
Figure 2. Locations of randomly selected scouring samples.These numbers are cross-referenced for
the photographs in Appendix B.
The final on-site walk-through was conducted on February 1, 2017. During the walk-through, all
construction plan specifications,the as-built survey, and installation items were reviewed and compared
to the build.The wavebreak structure installation was determined by the project engineer to be within
the pre-approved construction tolerances.
CSA-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 8

4. As-Built Summary
Following construction completion,the wavebreak structure was surveyed to verify it was built within
the designated footprint and aligned in the correct location.Warning signs and signal lights were
surveyed to confirm heights were within specifications from the U.S. Coast Guard Private Aids to
Navigation Permit. Following the on-site as-built survey,data was processed and drawn in CAD.The
drawings were then reviewed by SEPI staff and the project engineer. During the as-built review the
engineer confirmed the as-built location,alignment and components were correct and construction
installation followed the pre-approved construction plan drawings (Appendix A;Wave Attenuation
Structure Design and As Built Survey,Sealed).
5. References
Fonseca, M.S. 1996.The role of seagrasses in nearshore sedimentary processes:a review. Pp. 261-286.
In: Roman,C. and K. Nordstrom (eds.), Estuarine Shores: Hydrological, Geomorphological and
Ecological Interactions.Wiley, NY.
Fonseca,Mark and Susan S. Bell. 1998. "Influence of Physical Setting on Seagrass Landscapes near
Beaufort,North Carolina, 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. 2015. Memo on 9 June, 2015 from Mark Fonseca to Kathy Herring at NCDOT RE: Bonner
Bridge Seagrass Mitigation Project (State Project 32635.1.3; TIP B-2500) Task B (Site
Verification)Letter Report.
Google Earth Imagery,2004,2006,2008,2009,2011,2014.
Koch, E.W., L.P. Sanford,S.Chen, D.J.Shafer,J. M. Smith. 2006. Waves in seagrass systems: review and
technical recommendations. RDC TR-06-15.
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
NCDOT.2012. High Resolution Aerial Photography. NCDOT.2015. High Resolution Aerial Photography.
NCDWQ 401 Water Quality Certification Pursuant to Section 401 of the Federal Clean Water Act with
ADDITIONAL CONDITIONS for the Proposed Replacement of the Herbert C.Bonner Bridge over
Oregon Inlet in Dare County,Federal Aid Project No. BRNHF-0012(48),TIP B-2500(Phase I).
NCDWQ Project No.20120629.September 7,2012.
Stephan, D.C.,W.J. Goldsborough,J.H. Dunnigan, P.A. Sandifer. 1997. Submerged aquatic vegetation
policy. ASMFC Habitat Management Series#3. 15p.
CSA-NCDOT-FL-17-1830-2845-07-REP-01-FIN 9

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-NCDOT-FL-17-1830-2845-07-REP-0I-FIN 10