2023 SAV Survey Report

Hatteras Inlet 2023 Early Season SAV Survey
PREPARED FOR
Dare County, North Carolina
Coastal Protection Engineering of North Carolina, Inc.
COASTAL
PROTECTION
ENGINEERING
August 2023
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1. INTRODUCTION
The North Carolina Division of Coastal Management (DCM) issued Major CAMA Permit #129-
16 on December 20, 2016 and the United States Army Corps of Engineers (USACE) issued a
Department of Army (DoA) Individual Permit #SAW-2016-02140 on March 1, 2017 to Dare
County for the County's proposed Hatteras Inlet Channel Maintenance Project. As stated in the
permit application packages, Dare County was seeking permits that would allow for the utilization
of USACE dredges to conduct maintenance dredging within South Ferry Channel in an attempt to
reestablish the navigability from Ocracoke Island and Hatteras Island into Hatteras Inlet. Dredging
activities would be performed by USACE-owned dredge plants (sidecast dredge and special
purpose dredges) within a 150' wide channel excavated to -12 ft. MLW depths from within the
proposed South Ferry Channel corridor. Material excavated by a special purpose dredge would be
disposed in a nearshore disposal site in the Atlantic Ocean just south of Ocracoke Island which
had been previously authorized for use by the USACE. The permits issued to Dare County for this
action specified that dredging would not be permissible outside the environmental dredge window
of April 1 to September 30 without prior approval from the Division of Coastal Management
(DCM) and USACE in consultation with appropriate resource agencies.
Since the issuance of the initial permits, several modifications to the project have been made and,
subsequently permits have been modified. These modifications include the widening of the
permitted channel from 150 ft to 200 ft, the ability to utilize the Miss Katie as an additional dredge
plant, and an increase in the extent of the dredge corridor by an additional 149 acres.
The most recent DoA permit modification included a condition that states:
SAV should be mapped prior to the start of dredging and again closer to the end of SAVgrowing
season. Mapping should include the edges of SAV beds and percent cover and composition of the
SAV community characterized. Monitoring reports will be provided to resource agencies at the
end of the growing season in which dredge events occurred.
In order to ensure that Dare County properly fulfills this condition, CPE, on behalf of Dare County
coordinated directly with the National Marine Fisheries Service (NMFS) to determine an agreeable
approach. In a letter dated April 1, 2022, NMFS recommended:
• Dare County should be required to follow a monitoring plan for all dredge events outside
of the moratorium described by the North Carolina Coastal Habitat Protection Plan for
the Northern Outer Banks (i.e., when dredging occurs from April 1 to September 30). SAV
should be mapped prior to the start ofdredging and again closer to the end ofSAVgrowing
season. Mapping should include the edges of SAV beds and percent cover and composition
of the SAV community characterized. Monitoring reports should be provided to resource
agencies at the end of the growing season in which dredge events occurred.
• Dare County should be required to maintain a 300 foot buffer between SAV and all
dredging and disposal areas. The buffer should begin at either the channel or discharge
location, whichever is closest to the SAV beds.
It was determined that an in -situ "start of growing season" SAV surveying effort should be
implemented to determine if any SAV resources are located within 1,000 feet of the area(s) to be
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dredged during maintenance operations outside of the environmental dredge window spanning
between April 1 through September 30 any given year. Because this new permit condition was
issued in late spring 2022, there was no time to perform an in situ early growing season SAV
survey and, rather, it was agreed that Dare County could utilize the data from the 2012/2013
APNEP SAV survey to determine the location of any SAV within 1,000 ft of the proposed
dredging area. That assessment was performed via a desktop survey. For the 2023 early growing
season survey, however, an in situ SAV survey was performed on June 8-9, 2023 to determine the
location of SAV resources in proximity to the possible dredging area to be performed outside the
environmental dredge window. The methods and results of this assessment are provide in the
following sections.
PAL 10I10101110][014MA
To determine the geographic scope of the "start of growing season" SAV survey, first, the
footprint of prospective dredging that may occur outside of the environmental dredge window
was identified based on the location of the March 2023 dredge location (Figure 1). Then, the
2013/2014 APNEP SAV survey data was overlaid to give an indication of the closest SAV
resources in proximity to the proposed dredging footprint. A 1,000' buffer was then ascribed to
those SAV resources to determine the survey area (Figure 1).
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Figure 1. Location of the possible dredging outside the environmental window along with the geographic
extent of the SAV survey area.
A UAS (unmanned aircraft system, or "drone") was flown over the SAV survey area near low
tide on June 8, 2023 between 7:42am and 8:40am at a height of approximately 100m. The winds
were light (0-8mph), sea state was calm, and the sun angle was low (>30 degrees). Four flights
plans were implemented to cover the entire SAV Survey area Once flown, the images were
processed via SiteScan in an attempt to create a comprehensive orthomosaic image of the SAV
area. Due to SiteScan's inability to "stitch" together many of the images into the orthomosaic,
each individual image was reviewed in an attempt to identify SAV. The geotagged coordinates
from three images that contained features that appeared to be SAV were noted and plotted in
Google Earth. These areas along with five additional areas ideintified within the orthomosaic
derived from SiteScan were then visited on the morning of June 9 2023 (similar weather/sea state
conditions as on the 8"'). The sites that were groundtruthed and contained SAV were then
assessed to determine the percent cover of SAV within three haphazardly placed lm2 quadrats.
The species of seagrass within each quadrat was also determined.
3. RESULTS
The orthomosaic created by SiteScan only provided coverage of approximately 40% of the entire
survey area Much of the remaining survey area, however, contained waters deeper than -6'
NAVD88 and, therefore, due to SAV's depth limitations, the resource would not be expected to
grow there. That said, possible SAV was visually identified in several areas within the
orthomosaic and, upon review of the images that were not able to be "stitched" into the
orthomosaic, five (5) locations were identified for groundtruthing. In addition, three (3) additional
locations containing suspected SAV resources from within the domain of the orthomosaic were
groundtruthed. Collectively, eight (8) sites were groundtruthed viathe deployment of haphazardly
placed lm2 quadrats within the groundtruthing locations (Table 1 and Figure 2).
Table 1. Percent cover and species identified at eroundtruthed sites.
Groundtruth
Site
Replicate
% Cover
Species
A
1
0
N/A
2
0
N/A
3
0
N/A
B
1
0
N/A
2
0
N/A
3
0
N/A
C
1
0
N/A
2
0
N/A
3
0
N/A
D
1
0
N/A
4I

2
0
N/A
3
0
N/A
E
1
0
N/A
2
0
N/A
3
0
N/A
F
1
50
H. wri htii
2
60
1 H. wri htii
3
50
H. wri htii
G
1
35
H. wri htii
2
45
H. wri htii
3
30
H. wri htii
H
1
30
H. wri htii
2
30
H. wri htii
3
30
H. wri htii
Figure 2. Location of groundtruthed sites and the orthomosaic created during UAV flights on June 8, 2023.
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As depicted in Table 1, no SAV was located at groundtruthing sites A, B, C, D, and E. Sites A,
B, C, and D were all confirmed to contain sandy bottom in —3' water depth with no SAV
resources in proximty. Site E contained dark detritus in —l' of water depth with no SAV
resources in proximity. Sites F, G, and H were all confirmed to contain the seagrass species
Halodule wrightii.
Once the seagrass at Sites F, G, nad H were confirmed, it was possible to delineate the extent of
the SAV resoure within the survey domain, as depicted by the blue border in Figure 3. As a
comparison, the 2019/2020 APNEP SAV survey results are shown in Figure 4 with an orage
border. The closest SAV habitat delineated via UAS on June 8, 2023 to the northern border of
the permitted Hatteras Connector Channel Corridor is 630'. The closest the delineated SAV
resource is to the March 23, 2023 dredge area (the area where dredging could hypothetically be
dredged again during the 2023 environmental dredge window) is 1,100'.
Figure 3. Location of SAV resources delineated during the June 8, 2023 aerial survey and the 2019/2020
APNEP SAV survey.
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