FINAL_SAV_SUMMARY_B4929_2022

North Carolina Department of Transportation
Surf City Bridge
Submerged Aquatic Vegetation (SAV) Monitoring Summary
NCDOT WBS No. 40233.1.1
Surf City, NC
Pender County

Prepared For:

NC Department of Transportation
Raleigh, North Carolina

Contact Person:
Tyler Stanton
Biological Surveys Unit
North Carolina Department of Transportation
[e-mail]
1598 Mail Service Center
Raleigh NC 27699-1598

June 2022

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

TABLE OF CONTENTS

1.0 INTRODUCTION
2.0 BACKGROUND AND MINIMIZATION MEASURES
3.0 PROJECT AREA
4.0 MONITORING METHODS
5.0 MONITORING RESULTS
5.1 PRE-CONSTRUCTION
5.2 POST CONSTRUCTION
6.0 RESULTS
6.1 PRE-CONSTRUCTION
6.2 POST CONSTRUCTION
7.0 SUMMARY
TABLES
TABLE 1. PRE-CONSTRUCTION DATA
TABLE 2. POST CONSTRUCTION DATA
FIGURES
FIGURE 1. PROJECT STUDY AREA INDICATING SAV HABITAT SURVEY AREA
FIGURE 2. SAV SURVEY QUADRAT AREA

1.0 INTRODUCTION
The N.C. Department of Transportation constructed a 65-foot-tall, $53 million bridge to replace
the old swing bridge over the Intracoastal Waterway on N.C. 50/210 in Surf City. The bridge
was opened to traffic on December 4, 2018.

In accordance with Coastal Area Management Act (CAMA) permit number 60-16, Submerged
Aquatic Vegetation (SAV) was monitored in the alignment of the new Surf City Bridge before
construction and for two years post construction. The findings of this monitoring effort are
summarized in this report.

2.0 BACKGROUND and MINIMIZATION MEASURES
Surveys conducted on August 23, and September 25, 2012, by the NC Division of Marine
Fisheries (NCDMF) and NCDOT Biological Surveys Unit staff found four to five very small
patches (diameter less than 1 foot) of sparse widgeon grass (Ruppia maritima) located within
the proposed bridge drip line.

Direct impacts to the SAV habitat were avoided during construction The typical bridge span
length was extended to 141.5ft over the SAV to minimize indirect impacts to SAV and direct
impacts to wetlands.

Based on the proposed profile grade and deck depth, the bridge has a minimum of 38’ of
clearance over the SAV location, therefore minimizing the shade impacts.

To avoid direct impacts to the SAV area on the north side of the bridge, the temporary work
bridge was constructed only on the south side with fingers extending across the width of the
bridge during construction. In addition, no other bottom-disturbing activities occurred in the
SAV habitat area indicated in Figure 1.

Minimization measures taken to minimize impacts to SAV in accordance with CAMA permit
#60-16 issued on 6/2/16 included:
• Conduct SAV surveys for 2 years pre construction and 2 years post construction
• All bottom disturbing activities occurred outside the in-water work moratorium of April
1 to September 30.
• The bridge design spanned the entire SAV habitat area
• The bridge has a vertical clearance of 65ft above mean high water and a horizontal
clearance of 120ft, minimizing shading impacts

FIGURE 1. PROJECT STUDY AREA MAP INDICATING SAV SURVEY AREA

FIGURE 2. SAV SURVEY QUADRAT AREA

4.0 MONITORING METHODS

The pre-construction 2013 monitoring was conducted in June, July, August, and September by
biologists from NCDOT and CZR Incorporated. Preconstruction surveys in 2016, and post
construction surveys in 2019 and 2020 were conducted by biologists from SEPI, once in the
Spring and once in Summer 2016. 2019 and 2021 post construction SAV surveys were
conducted in the spring, mid-summer, and late summer of both years.

All surveys were conducted on the existing 0.21-acre site; located west of the Atlantic
Intracoastal Waterway within the Alternate 17 alignment (Figure 1). The survey included
ground-truthing of vegetation composition of existing SAV within the established 50’ X 180’ and
an additional 45’ X 40’ survey area was added in 2019.

Survey data collected included the presence or absence of SAV, species type, patch size and
percent crown cover within the study area. Water quality parameters collected included
Salinity and secchi depth.

The survey area was subdivided into eight quadrats (25’ X 45’). An additional quadrant 9
(40’x45’) was added to encompass a 400 square foot area of SAV habit under the bridge (Figure
2). The crown density scale was used to estimate percent cover of SAV beds located in the site
survey area. To maintain site set up precision, a Trimble GPS Geo 7 series handheld with Zephyr
antenna was used to establish the four corners of the (50’ X 180’) site previously surveyed
within the Alternative 17 bridge alignment. Due to the lack of tide gauge data at the site
location, tide chart data from New Topsail inlet was evaluated and compared to visual spot
checks from the survey location. The tidal information confirmed the ability to conduct the
survey within an allowable tide cycle and keep track of the tide during data collection.

Observers reported species, number of patches and percent cover of SAV within each belt
transect. The spring survey was conducted during flood tide starting in quadrat 8, continued
north on the eastern quadrats to quadrat 2, then traversed from quadrat 7 and continued north
to quadrant 1. Following completion of the original survey area, quadrant 9 belt transects were
surveyed from the south to north direction. The pathway during the survey was determined by
the tidal current and water clarity. Observers walked through transects due to shallow water
depths and used aquascopes to help during observations.

SAV species observed in the project area include eelgrass (Zostera marina) and widgeon grass
(Ruppia maritima). Eelgrass is a temperate species at the southern limit of its Atlantic range in
North Carolina and widgeon grass (Ruppia maritima) grows best in moderate salinity but has a
wide range of salinity tolerance.

5.0 MONITORING RESULTS

SAV Monitoring Results are presented in the following tables.

TABLE 1. PRE-CONSTRUCTION DATA
June 2013 July 2013 Aug 2013 Sept 2013 June 2016 Aug 2016
Number of
transects with
SAV (40 total
transects)
39 33 34 11 12 21
Species Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera
Percentage of SAV
cover
<5% <5% <5% <5% <5% <5% <5% <5% <5% <5% <5% <5%
Number and
diameter of
patches
35
Patches
or sprigs
31
Patches
or sprigs
31
Patches or
sprigs
25
Patches
or sprigs
32
Patches
or sprigs
16
Patches
or sprigs
Not
Available
Not
available
14/2-6” 5/3” 3/1-3” 31/0.5-
2”
Salinity 34.25 (PSU) 30.18 (PSU) 36.25 (PSU) 36.68 (PSU) 29.63(PSU) 28.2 (PSU)
Secchi >16.5” >13.5” >20.5” >10.0” >24” >18”

TABLE 2. POST CONSTRUCTION DATA

April 24-25,
2019
July 8-9, 2019 September 18-
19, 2019
March 30-31,
2020
July 14-15 2020 Aug 26-27,
2020
Number of
transects with SAV
(48 total
transects)
1 24 4 4 3 5
Species Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera Ruppia Zostera
Percentage of SAV
cover 0 <5% <5% <5% <5% 0 <5% <5% <5% <5% <5% 0
Number and
diameter of
patches
0 1/6” 26/1-4” 17/1-3” 5/1-2” 0 5/1-2” 3/3-4” 3/1” 1/1” 5/1” 0
Salinity 32.57ppy 31.87ppt 32ppt 28ppt 24ppt 32.71ppt
Secchi >22.5” >22.75” 24” >14.5” >22” >14.8”

6.0 RESULTS
6.1 PRE-CONSTRUCTION

During the June and July 2013 surveys, surveyors observed two to four patches each of both
eelgrass and widgeon grass approximately one to two feet in diameter. These larger patches
were absent in subsequent surveys, and smaller patches (less than one foot diameter) and
many single sprigs and rhizomes became the dominant forms of both SAV species. Coverage
and presence of algae and bryozoan species, like the SAV, decreased throughout the growing
season.

The salinities ranged from 28.2 to 36.68 practical salinity units (PSU) throughout the 2013 and
2016 surveys. The highest salinity was observed during the September 2013 survey and the
lowest in August 2016. The best visual water clarity was observed during the June 2016 survey
with a Secchi depth measuring greater than 24.0”. Water levels during the SAV surveys ranged
from 0.0” to 29.75”. Increased sedimentation was observed throughout the site during both
August surveys and the September 2013 survey.

Throughout the duration of the pre-construction surveys a decrease in the percentage of SAV
was observed. Seasonal annual comparisons of number of transects with SAV showed a decline
from 39 in June 2013 to 12 in June 2016. When comparing August 2013 to August 2016 a
decline from 34 transects having some amount of SAV to 21 (Table 1). Recorded SAV field
observations showed a seasonal transition displaying a reduction in seagrass beds, increased
sedimentation and increased number of aquatic worm casings infused with SAV. Many times,
surveyors had to distinguish between actual rooted SAV rhizomes and the occurrence of SAV
sprigs incorporated into worm casings buried in sediment. By the August and September 2013
surveys, SAV was only observed as single sprigs/rhizomes.

6.2 POST CONSTRUCTION

Estuarine species observed during the post construction surveys were widgeon grass (Ruppia
maritima) and eelgrass (Zostera marina). During the 2019 and 2020 surveys salinity ranged
between 22.71 and 34 parts per thousand (ppt). Secchi depths ranged from 14.5” to 22.75”
and water levels ranged from 0.0”- 38.0” during the surveys. Estimated percent cover of SAV
did not exceed 5 percent in any transects or quadrats during the post construction surveys. The
single largest patch of SAV was a 6” diameter patch of Zostera found in April 2019.

The largest amount of SAV was observed in July 2019 with 26 patches of Ruppia and 17 patches
of Zostera. None of these patches were greater than 4” in diameter. Only 5 patches of grass
were observed in September 2019 and no more than 5 patches of grass were observed in 2020
with diameters ranging from 1-4”.

7.0 SUMMARY

The majority of SAV observed during all surveys both before and after construction of the Surf
City Bridge were single sprigs or small (<6”) patches and coverage decreased throughout the
growing season in all years surveyed.

Based on minimization measures taken during design and construction, plus the limited value
of any real ecological function from the SAV found here, it is considered that this project did not
have any deleterious impact to Seagrass or Seagrass habitat that would require mitigation from
the NCDOT.

Zostera marina observed underwater, SEPI, August 16, 2016

Sediment covered SAV observed underwater, SEPI, August 16, 2016

Ruppia, March 20, 2020

Zostera, March 2020

Ruppia, July 2020