FINAL_NC24_LS_SAV_Monitoring_Plan_V3_5_4_22

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North Carolina Department of Transportation
NC 24 Causeway Living Shoreline
Submerged Aquatic Vegetation (SAV) Monitoring and Mitigation Plan
NCDOT WBS No. 49083.1.1
Swansboro, NC
Onslow/Carteret County

Prepared For:

NC Department of Transportation
Raleigh, North Carolina

Contact Person:
Brian Lipscomb
Hydraulics Unit
North Carolina Department of Transportation
[e-mail]
1598 Mail Service Center
Raleigh NC 27699-1598

May 2022

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Prepared by:

8601 Six Forks Road, Forum 1 Suite 700
Raleigh, NC 27615

Contact Person:

Kathy Herring
Senior Project Scientist
[e-mail]
919-971-4367

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TABLE OF CONTENTS

1.0 INTRODUCTION AND BACKGROUND
2.0 PROJECT AREA
3.0 CONSTRUCTION AND IMPACT SUMMARY
4.0 PROPOSED MITIGATION AND MONITORING PLAN
5.0 MONITORING
5.1 PRECONSTRUCTION
5.2 DURING AND POST CONSTRUCTION
TABLES
TABLE 1. SUMMARY OF SAV IMPACT AREA
FIGURES
FIGURE 1. VICINITY MAP
FIGURE 2. PROJECT STUDY AREA
FIGURE 3. POTENTIAL SAV IMPACT AREA

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1.0 INTRODUCTION AND BACKGROUND
In collaboration with the NC Coastal Federation (NCCF), the NC Department of Transportation
(NCDOT) has proposed to construct a living shoreline adjacent to the causeway at NC 24 in
Swansboro, NC to protect this critical roadway from further damage by erosional forces from
storm surge, wave action, and sea level rise. The living shoreline will also restore and protect
vital salt marsh and oyster habitat in Bogue Sound and the White Oak River.
The project concept and design is in accordance with the Governor’s Executive Order 80 (EO 80)
published in 2018 which tasks the NCDOT with integrating “climate adaptation and resiliency
planning into their policies, programs, and operations (i) to support communities and sectors of
the economy that are vulnerable to the effects of climate change and (ii) to enhance the
agencies’ ability to protect human life and health, property, natural and built infrastructure,
cultural resources, and other public and private assets of value to North Carolinians”.
This project will not only protect a vital NC roadway, but also help establish design,
coordination, and permitting parameters moving forward so that the NCDOT and cooperating
agencies can address coastal infrastructure issues resulting from rising sea level while
maintaining, protecting, and enhancing the coast’s vital biologically diverse natural habitats and
their flora and fauna.

2.0 PROJECT AREA
The project is located between Swansboro and Cedar Point, NC where the White Oak River
enters Bogue Sound (Figure 1). The substrate within the project study area consists of sand and
muck with no areas of hard bottom noted. Water depths range from the shoreline (0 foot) to
approximately -11 feet mean lower low water (MLLW) in the open water channel. Saltwater
marsh, predominately Spartina alterniflora, is present on site.
The project area is in the vicinity of known submerged aquatic vegetation (SAV) habitat
although no actual plants have been observed here during surveys performed by NCDWR in
previous years (Submerged Aquatic Vegetation Monitoring | APNEP (nc.gov), and by RK&K in
2020. However, this area has recently experienced what can be referred to as a “mast year”
(Fonseca and Uhrin, 2009) where extraordinary numbers of seeds germinate resulting in
significant new eelgrass growth in areas long devoid of cover. This may be contributed to the
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recent change in the physical nature of the area from some filling in of the existing channel,
resulting in a reduction of wave energy in the new growth area.
High salinity estuarine SAV species observed in the project area in 2022 include eelgrass
(Zostera marina). Eelgrass is a temperate species at the southern limit of its Atlantic range in
North Carolina.
Due to the lack of SAV presence at this site in previous surveys, it is suspected that the eelgrass
seed germination that occurred in 2022 will not survive through the summer months and
therefore no consistent habitat would be established. The occurrence of these “mast years” is
episodic, and recruitment varies at individual sites (person conversation, Mark Fonseca,
4/20/22).
FIGURE 1. VICINITY MAP

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FIGURE 2. PROJECT STUDY AREA MAP

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3.0 CONSTRUCTION AND IMPACT SUMMARY

Based on preliminary design, the footprint of the constructed living shoreline will occupy
approximately 0.56 acres of bottom habitat currently occupied by sparce patches and sprigs of
eelgrass (Figure 3, and as seen in the picture below). Some of this 0.56 ac area will be
converted to oyster and marsh habitat that will remain underwater (Table 1).

Table 1. Summary of SAV Impact Area
Total Area 0.56
Rock fill 0.18
Oyster Structure 0.04
Salt Marsh 0.07
Sand 0.24*
*Remains potential SAV habitat, 0.24ac is sand fill, 0.03ac is outside of the sills/oyster structures and no fill will be
placed in this area, but could be impacted during construction

Any impacts of other SAV are unknown at this time due to their temporal and ephemeral
nature.
Photo of eelgrass in the project area 4/11/22

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FIGURE 3. POTENTIAL SAV IMPACT AREA

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4.0 PROPOSED MITIGATION AND MONITORING PLAN
The proposed monitoring plan is designed to address the following:
• Document the presence and coverage of SAV and SAV habitat in the project area and
determine if the recent (2022) recruitment of Zostera marina (eelgrass) persists
• Document any changes to the physical nature of the project area through time
• Document additional habitat makeup and coverage after construction of the Living
Shoreline
o Oysters growing on structure (NC Coastal Federation monitoring methodology,
https://xfer.services.ncdot.gov/pdea/Temp/M-540%20SAV/.
o Marsh habitat gained (NC Coastal Federation monitoring methodology,
https://xfer.services.ncdot.gov/pdea/Temp/M-540%20SAV/.
o Fish habitat gained by reducing wave energy and preventing erosion
o SAV recruitment

This monitoring will be conducted preconstruction (ongoing), during construction, and for a
period of at least two years post construction. A post-construction 2-year period instead of a 5-
year period, as used in other SAV monitoring/mitigation plans, was proposed due to the
anticipated die off the current eelgrass and it not returning the following year. At the end of the
post construction monitoring period, the NCDOT will meet with the permitting agencies to
determine next steps based on the findings report. If it is determined from the monitoring
findings that the eelgrass from 2022 died back and did not return, or no other SAV is found in
the project area, this will be considered a no impact project for seagrass, requiring no
mitigation.

If it is determined that SAV persist in the project area, then the group will compare pre and post
construction SAV coverage, marsh coverage and oyster recruitment and determine if adequate
ecosystem services lift has occurred.

The monitoring/mitigation design for this project was developed in coordination with state and
federal permitting agencies to address any potential adverse impacts to Essential Fish Habitat in
seagrass and is being utilized in three NCDOT bridge projects along the NC coast (Rodanthe
Bridge, Mid-Currituck Bridge and Harkers Island Bridge). This monitoring and mitigation plan
design was developed to monitor seagrass for a period of time, post construction, to determine
any impact to seagrass. Data gathered and lessons learned from these projects will inform the
department and the permitting agencies in developing resource preservation and protection
strategies moving forward.

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5.0 MONITORING
SAV Surveys will be conducted twice annually during the growing seasons for area seagrass
(March/April and August/September) and after any significant storm event as determined by
NCDOT. The SAV surveys proposed will consist of low-level drone-based imagery. These
overflights would be conducted concurrently, based on water clarity and weather conductions,
with the twice annual monitoring. All seagrass and seagrass bed boundaries will be delineated
at the lowest practicable spatial resolution (~ 10 cm), rectified in a GIS and evaluated for
accuracy by ground-truthing points and margins of seagrass beds as directed by initial
interpretation of each imagery collection. Change analysis for seagrass cover will be performed
among successive imagery collections as well as the initial collection each time imagery is
flown.

5.1 PRECONSTRUCTION
The NCDOT will collect baseline SAV data during the growing season within the project area to
include SAV presence/absence, percent cover, and species composition and distribution. The
first two seasonal surveys were conducted on March 8 and September 28, 2020, as well as a
screening survey in February 2020. No SAV were found during these surveys. No survey was
conducted in 2021, however, there is data collected by NC Division of Water Resources that will
be included when it becomes available. Additional surveys will be conducted during the Spring
and Summer growing seasons until construction begins.

5.2 DURING AND POST CONSTRUCTION
Monitoring will occur throughout the project area as depicted in Figure 2 and consists of the
following metrics:
• GIS analysis of aerial photography to delineate changes to SAV beds as compared
to pre-construction baseline
• Ground truthing of GIS assessment. This will include a DGPS located delineation
of changes to the aerial GIS-based assessment and exclude areas discovered to
not be composed of live SAV (e.g., detritus)
• Seagrass species percent cover and composition/distribution via random quadrat
analysis

This plan may be adjusted as necessary to address construction schedule and methods. An
annual report will be submitted, as well as a final report at the end of the monitoring period. If
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the monitoring determines that the Zostera seed that germinated in 2022 does not survive
through the summer and does not appear again, or if no other seagrass occurs in the area
during the monitoring period, it will be considered that there was no consistent SAV habitat
established, and no mitigation required.
If the eelgrass does persist and/or other seagrass species occur during the monitoring period,
the NCDOT will compare the amount of SAV that was impacted by the structure to the amount
of additional ecosystem services uplift provided by the Living Shoreline in the form of oyster
recruitment, marsh addition or enhancement, and fish habitat added. If the additional
ecosystem services uplift is greater than or equal to the SAV impacted, no mitigation will be
required. If there is not adequate ecosystem uplift, NCDOT will agree to mitigate for SAV
impacts at a ratio of 1:1 using a method determined by the best available science at that time.

REFERENCES

Fonseca, M.S. and A.V. Uhrin. 2009. The status of eelgrass Zostera marina, as bay scallop
habitat: consequences for the fishery in the western Atlantic. Mar. Fish. Rev. 71:20-33.