20040561 Ver 4_Comment Response Letter to DCM 2021-04-16 AD_20210416

www.lmgroup.net • Phone: [phone] • Fax: [phone]
3805 Wrightsville Ave., Suite 15, Wilmington, NC 28403

April 16, 2021

Heather Coats
Division of Coastal Management
127 Cardinal Drive Extension
Wilmington, N.C. 28405-3845

Re: Major Modification to CAMA Permit # 91-14
Village of Bald Head Island, South Beach Renourishment Project
Bald Head Island, Brunswick County

Heather,

In response to your email dated December 29, 2020 relaying the NC Division of Marine Fisheries (DMF)
most recent comments, the Village of Bald Head Island (Village) has performed modeling of sediment
transport rates and has compiled additional information to address the concerns identified by NC DMF.
Specifically, the attached documents provide the following:

(1) Updated Borrow Site Discussion (engineering analysis) of borrow site existing and predicted physical
conditions (see Attachment A). This updated discussion includes a summary of results for requested
modeling of sediment transport potential. The modeled rates of sediment transport have been used
to calculate a predicted rate of infill at the selected borrow site based upon the proposed dredge
depths.
(2) Technical Memorandum describing the UNIBEST sediment transport modeling methods and results
(see Attachment B).
(3) Biological Monitoring Plan (Attachment C) that incorporates pre-project monitoring and
reference/control site monitoring for benthic infaunal communities. In an effort to document existing
conditions, the Village will initiate monitoring a minimum of one year in advance of project dredging.
Depending on the timing of a permit decision, the Village may be able to commit to more than one
year of pre-construction monitoring. The monitoring will include pre-project seasonal sampling to
better assess the time of year that benthic invertebrates may be most abundant.

Note that implementation of both the physical and benthic monitoring plans will yield several years of
data that can be used to evaluate bathymetrical and benthic community response to the proposed
dredging. In combination with the BOEM research effort, the data can be used to help inform future
permit decisions. The Village is committed to provide these data in collaboration with BOEM’s research.

As has been previously noted, there have been a number of avoidance and minimization measures
incorporated into the design and implementation of the proposed dredging project. Principally among
these measures have been the reduction of the extent of the dredge footprint and confining this
modification request to a one-time dredge event to be monitored for the assessment of physical and
biological recovery. In addition, the Applicant agrees to prioritize the use of Jay Bird Shoals should
adequate recovery of that sand source be demonstrated prior to the need for the next Village-sponsored
nourishment. Lastly, the project is to employ the protection measures identified by the South Atlantic
Fisheries Management Council (SAFMC) specific for dredge and fill projects in areas designated as Habitat
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Areas of Particular Concern (HAPC) as well as several other measures identified in the Applicant’s response
dated July 28, 2020. As a result, it is the position of the Applicant that the proposed project will not result
in a significant impact to fish species nor to EFH (as has been demonstrated for other dredging projects
routinely occurring within EFH and HAPC of North Carolina state waters).

We believe that the enclosed documents, in conjunction with our initial comment response letter (dated
July 28, 2020), and the commitment to the identified avoidance and minimization measures adequately
address DMF’s concerns. Should you have any questions regarding the information provided, please feel
free to contact me vial phone at 910-452-0001 or by email at [e-mail]. Thank you for your
time and assistance.

Sincerely,

Land Management Group (Agent)

Greg Finch
Section Manager

Encl: Attachment A: Updated Borrow Site Discussion
Attachment B: Technical Memorandum (UNIBEST Sediment Transport Modeling)
Attachment C: Biological Monitoring

Cc: Village of Bald Head Island
Olsen Associates, Inc.
Ronnie Smith, USACE

March, 2021 . 1
FRYING PAN SHOALS – BORROW SITE DISCUSSION
BACKGROUND
The Frying Pan Shoals (FPS) formation was first evaluated as a potential sand source for
purposes of beach restoration beginning in the 1970’s (Meisburger, 1977). That Reconnaissance
level work was carried out by the Coastal Engineering Research Center (CERC) for the
Wilmington District, USACOE. Both cores and sub-bottom survey comprised the majority of
the data acquisition performed for purposes of defining the spatial distribution of potential sand
sources located within FPS. At the time, isopachs of potential sand thickness indicated at least
1.4 billion cubic yards of potential beach quality sand located within the Frying Pan Shoals
formation. That global estimate of sand volume can be assumed to be conservative.
McNinch (2009) performed a Literature Review of Cuspate Forelands which included a
discussion of the implications of dredging Frying Pan Shoals by the Wilmington District,
USACOE. With respect to the latter, Dr. McNinch made the following initial observations
which are relevant to the siting of the proposed Village of Bald Head Island (VBHI) borrow site;
•“The most active region of sediment recharge to FPS is likely near the Cape Fear Point,
particularly along the crest of the shoal where it extends seaward from the subaerial Cape
Fear Point and the shore parallel sand bar that merges into FPS from the updrift beach”.
Note – the predominant updrift beach or shoreline northward of the Cape Point is known
as East Beach on BHI.
•Sediment along the flanks of FPS likely migrate crestward during swell conditions and
seaward when it reaches the crest”.
•“The crest of the shoal is likely planed-off during storm conditions, when waves are steep
and breaking occurs across the shoal, and sediment is transported to the flanks”.
ATTACHMENT A.

March, 2021 . 2
• “Sediment dredged from the northwest flank of FPS will likely recharge episodically
from sediment transported from the crest during storms, particularly during extratropical
nor’easters”.

Numerous individuals or organizations have performed estimates of littoral transport
along the every-varying shoreline components of the State of N.C. More recently, (Van Gaalen,
Tebbens and Barton, 2016) have summarized estimated sediment transport directions from
Northern Maine to Tampa Bay, FL. For the Cape Fear formation, the published estimated rates
for the two BHI shorelines which join to form the Cape Fear Point were are as follows:

• South Beach – 339,300 cubic meters annually toward the East.
• East Beach – 341,000 cubic meters annually toward the South.

This represents a potential net annual hypothetical rate of deposition to the Cape Fear
Shoal formation of 680,300 cubic meters (i.e. 813,215 cy). Note – annual monitoring of the two
Bald Head Island shorelines indicates that average annual transport rates should be less than that
estimated above, although sediment transport is documented to increase immediately after beach
restoration. As a result, the SWANN wave transformation model and the UNIBEST-CL+
modeling suite were implemented to compute the magnitude of alongshore sediment transport
potential which is directed towards Frying Pan Shoals on an average annual basis (Olsen, 2021).

The UNIBEST model predicts that the total gross sediment transport potential directed
toward Frying Pan Shoals is about 595,000 cy/yr, on average. Of this potential rate,
approximately 420,000 cy/yr are derived from East Beach, with the remaining 175,000 cy/yr
coming from South Beach (Figure 1). Based upon the available long-term oceanographic data,
595,000 cy/yr represents the average annual potential alongshore sediment source for Frying Pan
Shoals. Predicted gradients in sediment transport potential predict that South Beach is
accretional whereby East Beach is erosional, on average. These gradients along with the
differences in gross transport potential, suggest that deposition onto Frying Pan Shoals may
predominantly be sourced from East Beach. In reality, the documented stability of the two (2)
shorelines abutting Cape Fear is highly influenced by the configuration of the Point any one year.

March, 2021 . 3
That is to say, as a depositional feature, the “foot print” of the Point fluctuates as a result of the
occurrence of major tropical storms or hurricanes which affect this section of the N.C. coast. For
example, Hurricanes Matthew, Florence, Dorian and Isaias have impacted the two Bald Head
Island segments of shoreline between 2016 and 2020. The observed effect of each major storm
event is to cause strong alongshore currents which breach the physical attachment of FPS to the
shoreline – thereby resulting in the episodic release of depositional material comprising the
Point. Simplistically, as the Point accretes seaward, both shorelines benefit – whereas when the
Point erodes due to storm effects – both adjacent shorelines suffer temporal recession. A
photographic chronology of the Cape Fear Point varying shoreline conditions between 2008 and
2020 is included as Figure 2.

In 2009, the Wilmington District, USACE acquired some 31 Vibracores in proximity to
the western side of Frying Pan Shoals as part of a sand search for the Brunswick County Shore
Protection Project. The District then contracted with Catlin Engineers and Scientists of
Wilmington, N.C. to analyze the cores. A summary of findings was provided to the Wilmington
District on 27 May 2010 (Catlin, 2010). The report included core logs, grain size classifications
and various summaries of the sediment characteristics encountered suitable for beach restoration.

In 2016, Olsen Associates, Inc. initiated a comprehensive multi-phase Sand Search
Investigation of Frying Pan Shoals (Olsen, 2016) intended to allow for the eventual permitting of
a single-use borrow site within State waters.

The chronological Task Logic for the phased Sand Search sponsored by the VBHI can be
summarized as follows:

1. A coarse grid survey was performed to update general bathymetric shoal features within
the 3-mile limit. Mapping utilizing federal NOS data was not reliable for purposes of
coring.

2. A Phase I (coarse grid) Cultural Resource Investigations was carried out to eliminate any
dense clusters of magnetic anomalies which would indicate a high probability of a ship

March, 2021 . 4
wreck site. It was determined that no level of geotechnical investigation would be
performed in any such areas identified.

3. Based upon 1.) and 2.) above, a Vibracoring Plan was formulated so as to maximize
potential depths of beach compatible sediment, with the intent of minimizing future
conflicts with probable cultural resource locations.

4. Subsequent to coring, a sub-bottom survey was performed to extend the data base
between cores and to areas of interest where cores would not be feasibly (or safely)
acquired due to shallow depths, breaking waves, or tidal surging.

5. In consideration of the results of the seismic survey, Vibracore logging and laboratory
analyses of sediment samples over depth, a generalized borrow area was defined by
Olsen Associates, Inc. – all of which is documented in a comprehensive report (Olsen,
2016).

6. Subsequently, a Phase II Cultural Resource Investigation was performed of the selected
borrow area in order to eliminate areas of avoidance recommended by the project marine
archaeologist. The final Permit Application was based upon the refined borrow site
limits which included buffers between, or around unverified anomalies and future
dredging activities.

BORROW SITE SELECTION

The selection of the proposed 188.7 A. area borrow site was determined on the basis of
both environmental and physical characteristics. Although the engineering design characteristics
of the proposed borrow site are a matter of record (Olsen, 2016), in order to minimize
environmental impacts, the following relevant selection parameters were prioritized:

• Borrow Site Recovery – As recommended by McNinch (2009), the proposed area of
excavation is principally located on the crest of the existing shoal formations which is the

March, 2021 . 5
most-high energy (i.e. dynamic) portion of the shoal. This will assure rapid post-
construction deposition of new material into the excavated area. Although it is not
possible to reliably “numerically model” the infilling processes due to the complexity and
dynamic characteristics of the shoal’s everchanging bathymetry, it can be reliably
estimated based upon the anticipated volume of material which episodically enters the
shoal formation from the two (2) shorelines on BHI which form the Cape Point. If one
assumes only a net average annual transport of say 595,000 cy per year to FPS from the
two abutting shorelines (as predicted by the UNIBEST model), then the theoretical
“recharge” to the shoal formation (relative to a 2 Mcy dredging project) would be
approximately 4 years or less. To that end, it has been documented through monitoring
of a comprehensive 2000 beach fill by the Corps of Engineers – that eastward directed
average annual littoral transport after beach restoration can be greater. Hence, after fill
placement of sediments excavated from a FPS borrow site placed along the easternmost
half of South Beach, it is fully expected that much of the material placed will eventually
return to the FPS formation. A conservative engineering estimate of the ability of the FPS
borrow area to recover 80-90% of the neat volume removed for beach fill is 5 to 10 years.

• Borrow Site Substrate – More importantly, for purposes of ensuring rapid benthic
recovery, the post-excavation substrate should be self-similar to existing prior to
dredging. This is addressed two ways: a) by ensuring that the depth of excavation is
strategically limited such that the sediment exposed (post-dredging) has similar granular
characteristics to the native seabed, and b.) by ensuring that material transport into the
excavated area will be rapid and continuous. Under such constraints, benthic recovery of
the “disturbed” seabed typically occurs within 1-year.

• Minimization of the Area Impacted – For purposes of reducing temporal dredging
impacts to pre-existing benthic resources, it is desirable to design a borrow area having
the smallest effective “foot print”. For this site, this is accomplished principally through
the utilization of a cutter suction dredge, as well as the specification of a dredged area
with the thickest layer of sediment available – which for the FPS formation is
synonymous with the centralized portion of the shoal. Although the depth of excavation

March, 2021 . 6
at these shallow locations may exceed 15 ft. below the seabed, it is reliably predicted that
shoal dynamics at this location will quickly reduce the effective borrow depth due to
rapid infilling and slope adjustments. Note – A secondary benefit of a cutter suction
dredge is that it does not “entrain” fishery resources – in contrast to a hopper dredge
which represents a highly quantifiable threat to fishery resources during the dredging
process including endangered species such as the Atlantic Sturgeon.

• Selected Borrow Site Location – The northernmost limit of the proposed borrow site is
located approximately one (1) mile southward of the Cape Fear shoreline. As depicted
by Figures 3, 3 & 4, sand transported from the East Beach and South Beach shorelines
migrates southward in the form of small discrete bars or shoals along the shallow crest of
the FPS formation. Some 20 years of islandwide shoreline monitoring by the Village of
Bald Head Island documents that the genesis of the small “shoals” is often associated
with the episodic release of sand which accretes for short periods of time at or adjacent to
Cape Fear. Any such accretional feature is generally not long lived and is quickly eroded
and released southward during the more energetic winter wave conditions, as well as both
extra-tropical and tropical storm events. As shown on the attached aerial photography
documenting shoal conditions in 1993, 2015 and 2019, the most emergent shoals extend
about 1.5 to 2 miles southward of Cape Fear. Accordingly, the subject borrow site is
located sufficiently southward of Cape Fear so as to take advantage of potential borrow
sand recovery associated with this phenomena, but not so close to the island shoreline
that it would impact those processes which move sand southward along the crest of the
formation after “release” from the two Cape Fear shorefronts and episodically to some
degree from the Point itself.

• Frequency of Occurrence – The Applicant’s coastal engineering consultant has opined
that based upon the existing precepts of the Wilmington Harbor Sand Management Plan,
which episodically place high quality maintenance sand on BHI, it could be necessary to
construct an interim locally sponsored beach fill project every 8-12 years, mol. It is
acknowledged however, that subsequent to the first use of the FPS borrow site, it could

March, 2021 . 7
be possible that the Agency preferred borrow area located at Jay Bird Shoals (JBS) may
have sufficiently “recovered” by that time. As such, it could potentially provide a viable
alternate sand source in lieu of the FPS borrow area. Surveys of the JBS borrow area are
performed annually for purposes of determining physical recovery. Those results are
published annually as part of the Applicant’s island-wide monitoring program.

• Confirmation of Impact and Recovery Predictions – The VBHI as Applicant for the
development of the one-time-use FPS borrow site discussed herein acknowledges the
need for the monitoring of physiographic, sedimentary and benthic recovery within the
proposed area of excavation. Comprehensive Monitoring Plans will be submitted under
separate cover for consideration by resource agencies.

March, 2021 . 8
REFERENCES

Catlin, Engineers and Scientists, 2010, Brunswick County Beaches Renourishment Study
– Frying Pan Shoals Soil Testing and Compatibility Analysis and Geotechnical Report”,
report prepared for Wilmington District, USACOE, Catlin Wilmington, N.C. 28404.

McNinch, J.E., 2009, Literature Review of Cuspate Forelands – Implications of dredging
Frying Pan Shoals”, Report prepared for Wilmington District, USACOE.

Meisburger, E.P., 1977. “Sand Resources on the Inner Continental Shelf of the Cape
Fear Region, N.C.,” U.S. Army Corps of Engineers, CERC, Ft. Belvoir, VA, Misc.
Report No. 77-1.

Olsen Associates, Inc., 2016. “Frying Pan Shoals – Sand Search Investigation”, report
prepared for Village of Bald Head Island. Olsen Associates, Inc., 2618 Herschel St.,
Jacksonville, FL 32204.

Olsen Associates, Inc., 2021. “Alongshore Sediment Transport Potential at Frying Pan
Shoals, North Carolina”, Technical Memorandum prepared for Village of Bald Head
Island. Olsen Associates, Inc., 2618 Herschel St., Jacksonville, FL 32204.

Van Gaalen, J.F.,: Tebbens, S.F., and Barton, C.C., 2016. Longshore sediment transport
directions and rates from northern Maine to Tampa Bay, Florida: Literature compilation
and interpretation. Journal of Coastal Research, 32(6), 1277-1301. Coconut Creek
(Florida), ISSN 0749-0208.

Figure 1
UNIBEST Predicted Gross Sediment Transport Potential at Cape Fear
Source: UNIBEST/SWAN model results
olsen associates, inc.4 March 2021
CapeFearApril 2011 PhotoMay 2008 PhotoShoalsClubMay 2014 PhotoApril 2010 PhotoMay 2020 PhotoApril 2017 PhotoFigure 2:Cape Fear shoreline conditions(2008-2020)
GRAPHIC SCALE0.501.0 MILESOUTH BEACHEASTBEACHBALD HEAD ISLANDATLANTIC OCEANPROPOSED BORROW SITEFEB.1993PHOTOCAPEFEARFIGURE 3
GRAPHIC SCALE0.501.0 MILESOUTH BEACHEASTBEACHBALD HEAD ISLANDATLANTIC OCEANPROPOSED BORROW SITEMARCH2015PHOTOCAPEFEARFIGURE 4
GRAPHIC SCALE0.501.0 MILESOUTH BEACHEASTBEACHBALD HEAD ISLANDATLANTIC OCEANPROPOSED BORROW SITEJUNE2019PHOTOCAPEFEARFIGURE 5
TECHNIAL MEMORANDUM
TO: Village of Bald Head Island
FROM: Steven C. Howard, P.E., Zak Bedell, E.I.T.
DATE: 4 March 2021
RE: Alongshore Sediment Transport Potential at Frying Pan Shoals, North Carolina
______________________________________________________________________________
The Frying Pan Shoals represent a large area of historically dynamic, shallow sand
deposits which extend toward the south-southeast off Cape Fear in North Carolina. In support of
an ongoing permitting effort to develop an offshore sand borrow area located on Frying Pan
Shoals, the applicant was required to quantify the shoaling potential along Frying Pan Shoals. In
order to accomplish this, the numerical models SWAN (Simulating WAves Nearshore) and
UNIBEST (UNIform BEach Sediment Transport) were employed in order to compute
alongshore sediment transport potential along the beaches both north and west of Frying Pan
Shoals.
The SWAN wave transformation model and the UNIBEST-CL+ modeling suite were
implemented to compute the magnitude of alongshore sediment transport potential which is
directed towards Frying Pan Shoals on an average annual basis. Wave data used as model input
was derived from a 15-year record (2005-2020) of hourly wave measurements collected at
NOAA Buoy 41303. The buoy is located about 31 miles south-southeast from the southern tip
of Cape Fear. A wave rose detailing the 15-year wave record at Buoy 43013 is shown in Figure
1.
The 15-year wave record was schematized into representative wave cases by traditional
bin sorting. The record was sorted into 16, 22.5-degree direction bins, 3 peak period, Tp, bins
(Tp ≤ 6.0 sec, 6.0 sec < Tp ≤ 9.0 sec, and Tp > 9.0 sec), and 4 significant wave height bins, Hs,
(Hs ≤ 1.0 m, 1.0 < Hs ≤ 2.0 m, 2.0 < Hs ≤ 3.0 m, and Hs > 3.0 m). Wave cases resulting from
the bin sorting were reduced according to incident direction and occurrence whereby only waves
arriving from between 11.25 and 281.25 degrees and occurring more than one hour per year, on
average, were considered. This resulted in a total of 114 representative wave cases, which are
descriptive of about 96.6% of the total 15-year wave record. The wave cases used for model
input along with relevant frequency information are listed in Table 1.
ATTACHMENT B.
Alongshore sediment transport potential at
Frying Pan Shoals, North Carolina
4 March 2021
Page - 2 - of 6

Figure 1: Summary of wave data collected between 2005 and 2020 at NOAA Buoy 41303.

Each representative wave case was numerically transformed from the location of the
NOAA buoy, across the highly complex Frying Pan Shoal bathymetry, to land using the SWAN
model. The SWAN model utilized two nested numerical model domains which reduced in
resolution from about 1,000 meters in the offshore to about 70 meters in the nearshore. Both
model domains combined include about 40,000 computational cells. The location of both model
domains used in SWAN is shown in Figure 2.

Bathymetric data used to describe offshore conditions was taken directly from the SWAN
model sued in a 2012 Delft3D morphological modeling study of the Cape Fear Entrance and its
surrounding beaches completed by Olsen Associates1. The nearshore bathymetry along Bald
Head Island’s south and east-facing shoreline was updated using beach profile survey data
collected in November 2020 by McKim & Creed. The beach profile surveys are spaced about
every 1,000 feet alongshore and extend about 3,000 feet offshore. The bathymetry input into the
SWAN model’s nested, nearshore domain is shown in Figure 3. The SWAN model was
previously calibrated and verified for the 2012 study using wave data measured at NOAA Buoy
41013 and several nearshore wave gauges. For this exercise, model settings were maintained at
the values arrived for the 2012 study.

1 Olsen (2012). “Calibration of a Delft3D model for Bald Head Island and the Cape Fear River Entrance, Phase I.”
Prepared for Village of bald Head Island. Olsen Associates, Inc. 2618 Herschel Street Jacksonville, FL
32204. April 2012.
Alongshore sediment transport potential at
Frying Pan Shoals, North Carolina
4 March 2021
Page - 3 - of 6

Table 1: 114 representative wave cases, NOAA Buoy 43013, 2005-2020.

1 0.359 439 1.31 0.8 4.35 23.5 62 1.048 1,282 3.83 0.8 5.19 158.5
2 1.245 1,523 4.54 1.4 5.2 23.6 63 1.139 1,394 4.16 1.3 5.44 158.4
3 0.110 134 0.40 2.2 5.74 22.3 64 0.039 48 0.14 2.2 5.79 156.8
4 0.117 143 0.43 1.7 6.44 26.8 65 1.503 1,839 5.49 0.8 7.1 155.8
5 0.136 166 0.50 2.4 6.41 25.8 66 2.570 3,144 9.38 1.4 7.11 157.8
6 0.011 14 0.04 3.8 6.88 27.1 67 0.785 960 2.87 2.4 7.46 158.4
7 0.018 22 0.07 0.7 11.13 25.6 68 0.147 180 0.54 3.4 7.92 156.8
8 0.018 22 0.07 1.3 9.27 24.6 69 0.322 394 1.18 0.8 10.65 153.6
11.25 to 33.75 TOTAL 2.014 2,463 7.35 70 0.585 716 2.14 1.4 10.57 154
9 0.572 700 2.09 0.8 4.66 46.1 71 0.291 356 1.06 2.4 10.64 156.9
10 2.451 2,999 8.95 1.4 5.35 47 72 0.208 255 0.76 3.8 10.37 157.6
11 0.190 232 0.69 2.2 5.74 48.2 146.25 to 168.75 TOTAL 8.637 10,568 31.53
12 0.053 65 0.19 0.7 7.49 47.9 73 1.895 2,319 6.92 0.8 5.06 180.6
13 0.677 828 2.47 1.7 6.44 49.1 74 1.998 2,445 7.29 1.3 5.44 180.8
14 0.772 945 2.82 2.4 6.73 49.4 75 0.030 37 0.11 2.2 5.79 180.4
15 0.086 105 0.31 3.5 7.29 49.7 76 0.521 638 1.90 0.9 6.66 178.1
16 0.070 86 0.26 0.7 11.49 49.3 77 2.974 3,639 10.86 1.5 6.99 179.9
17 0.044 54 0.16 1.3 11.52 48.9 78 1.228 1,502 4.48 2.4 7.58 180.3
33.75 to 56.25 TOTAL 4.915 6,014 17.94 79 0.155 190 0.57 3.4 8.01 179.7
18 0.485 594 1.77 0.9 4.96 65.8 80 0.065 80 0.24 0.7 12.36 178.1
19 2.135 2,612 7.79 1.4 5.49 65 81 0.155 190 0.57 1.7 9.89 178.6
20 0.159 194 0.58 2.2 5.78 64.4 82 0.389 476 1.42 2.5 9.57 180.9
21 0.749 917 2.73 0.7 7.67 71.4 83 0.334 409 1.22 3.9 10.08 180.7
22 1.950 2,386 7.12 1.6 6.65 67 168.75 to 191.25 TOTAL 9.744 11,925 35.57
23 1.873 2,291 6.84 2.4 7 65.9 84 2.273 2,781 8.30 0.8 4.88 202.8
24 0.278 340 1.01 3.3 7.69 65.8 85 2.660 3,255 9.71 1.3 5.38 203
25 0.962 1,177 3.51 0.8 10.24 71.5 86 0.032 39 0.12 2.1 5.78 203.4
26 0.481 588 1.76 1.2 10.77 72 87 0.190 232 0.69 0.9 6.51 201.2
27 0.024 29 0.09 2.3 13.33 73.9 88 1.993 2,438 7.27 1.5 6.78 202
28 0.052 64 0.19 4.2 10.93 69.1 89 0.911 1,115 3.33 2.4 7.41 202.4
29 0.338 414 1.23 0.8 5.15 90.3 90 0.132 162 0.48 3.4 8 202.9
56.25 to 78.75 TOTAL 9.486 11,606 34.62 91 0.021 26 0.08 1.8 10.4 197.4
30 0.477 584 1.74 1.4 5.43 88.5 92 0.163 200 0.59 2.5 9.31 197.7
31 0.024 29 0.09 2.2 5.78 87.8 93 0.194 237 0.71 3.7 9.74 199.5
32 2.684 3,284 9.80 0.7 7.7 91.1 191.25 to 213.75 TOTAL 8.569 10,485 31.28
33 1.678 2,053 6.12 1.4 7.44 90.8 94 1.846 2,258 6.74 0.8 4.59 223.3
34 0.437 535 1.60 2.4 7.31 87.9 95 2.812 3,440 10.26 1.3 5.27 223.6
35 0.051 62 0.19 3.3 7.93 86.7 96 0.053 65 0.19 2.2 5.83 224.6
36 3.695 4,521 13.49 0.8 10.24 91.2 97 0.045 55 0.16 0.9 6.42 219.3
37 2.691 3,292 9.82 1.3 10.91 92.3 98 0.843 1,032 3.08 1.6 6.56 220.8
38 0.254 311 0.93 2.3 11.64 93.9 99 0.631 772 2.30 2.4 6.98 222.9
39 0.107 131 0.39 4.1 11.31 91.8 100 0.099 121 0.36 3.5 7.86 223.6
78.75 to 101.25 TOTAL 12.098 14,802 44.16 101 0.011 13 0.04 0.7 12.1 225.2
40 0.387 473 1.41 0.8 5.26 113 102 0.016 19 0.06 4.0 9.33 222.4
41 0.477 584 1.74 1.4 5.36 113 213.75 to 236.25 TOTAL 6.356 7,775 23.20
42 0.017 21 0.06 2.2 5.73 112.4 103 0.485 593 1.77 0.8 4.11 245.6
43 4.353 5,326 15.89 0.7 7.76 113.1 104 0.673 824 2.46 1.3 5.04 245.1
44 2.499 3,057 9.12 1.4 7.59 113 105 0.056 68 0.20 2.3 5.7 249.2
45 0.475 581 1.73 2.3 7.53 114 106 0.042 51 0.15 1.8 6.4 243.3
46 0.044 54 0.16 3.3 7.89 113.2 107 0.159 194 0.58 2.6 6.65 246.7
47 4.752 5,814 17.34 0.8 10.23 112.3 108 0.052 64 0.19 3.4 7.13 248.7
48 4.409 5,394 16.09 1.4 10.97 112.2 236.25 to 258.75 TOTAL 1.467 1,794 5.35
49 0.712 871 2.60 2.4 11.31 112.7 109 0.208 255 0.76 0.8 3.99 268.7
50 0.193 236 0.70 3.8 11.33 113 110 0.457 559 1.67 1.4 5.08 270.3
101.25 to 123.75 TOTAL 18.318 22,411 66.86 111 0.092 113 0.34 2.2 5.73 270.2
51 0.530 649 1.93 0.8 5.28 135.7 112 0.016 19 0.06 1.8 6.27 267.5
52 0.732 896 2.67 1.4 5.39 135.3 113 0.125 153 0.46 2.5 6.44 270
53 0.025 31 0.09 2.2 5.77 135.5 114 0.048 59 0.18 3.5 7 268
54 3.796 4,644 13.86 0.8 7.59 133.7 258.75 to 281.25 TOTAL 0.946 1,158 3.45
55 2.606 3,188 9.51 1.4 7.48 134.7 11.3 to  281 TOTAL 96.575 118,163 352.50
56 0.585 716 2.14 2.4 7.54 135
57 0.097 119 0.35 3.4 7.91 136.8
58 2.303 2,818 8.41 0.8 10.14 132.3
59 2.640 3,230 9.64 1.3 10.49 133.5
60 0.485 594 1.77 2.4 10.97 134
61 0.226 277 0.82 3.8 11.05 135.5
123.75 to 146.25 TOTAL 14.025 17,162 51.19
avgPd (s)avgDir 
(deg)
Direction Bin 
(degrees)Case % Occ (%) # occ days/year
avgHs 
(m)
avgPd 
(s)days/year avgHs 
(m)
avgDir 
(deg)
Direction Bin 
(degrees)Case % Occ (%) # occ

Alongshore sediment transport potential at
Frying Pan Shoals, North Carolina
4 March 2021
Page - 4 - of 6

Figure 2: Numerical model domains for the SWAN wave transformation model. The red finely resolved
domain is nested within the more coarsely resolved blue model domain. The location of NOAA wave
buoy 43013 is shown, for reference.

Figure 3: Bathymetry input to the SWAN model.
Alongshore sediment transport potential at
Frying Pan Shoals, North Carolina
4 March 2021
Page - 5 - of 6

The results from the SWAN wave transformation along with the average annual
frequency of occurrence for each wave case (days/year) were used as input into the UNIBEST
model. In addition to incident nearshore wave conditions, the UNIBEST model requires beach
profile bathymetric data along transects of interest. For this study, the bathymetry along 41
beach profiles was extracted from the SWAN model domain, representing nearshore conditions
measured in November 2020. Of the 41 profiles, 11 are along the southern Bald Head Island
shoreline (AKA “South Beach”) and the remaining 30 profiles are on the eastern-facing island
shoreline (AKA “East Beach”). The resulting UNIBEST domain covers about 6 miles north and
about 2.5 miles west of Cape Fear. The locations of each beach profile correspond with
established physical monitoring locations spaced about every 1,000 feet along the island.

Transformed wave conditions from the SWAN model output were extracted at the
offshore limit of each UNIBEST beach profile, typically at a depth of about -5 m, MSL. The
UNIBEST model then transforms each wave to the shoreline while computing the cross-shore
distribution of alongshore sediment transport. Sediment transport computed by the UNIBEST
applied the Kamphius (2000) transport formula with the model parameters shown in Table 2.
Because the model is uncalibrated, the resulting sediment transport rates are considered to be
representative of average annual transport potential resulting from the input wave climate. The
model results are shown in Figure 4. The figure plots the computed alongshore gross sediment
transport potential towards Frying pan Shoals; i.e., either southward or westward.

Table 2: Wave and longshore sediment transport parameters for the UNIBEST CL+ model.

The UNIBEST model predicts that the total gross sediment transport potential directed
towards Frying Pan Shoals is about 595,000 cy/yr, on average. Of this rate, approximately
420,000 cy/yr are derived from East Beach, with the remaining 175,000 cy/yr coming from
South Beach. Based upon the available long-term oceanographic data, 595,000 cy/yr represents
the average annual potential alongshore sediment source for Frying Pan Shoals. Predicted
gradients in sediment transport potential predicts that South Beach is highly accretional whereby
East Beach is highly erosional, on average. These gradients along with the differences in gross
Alongshore sediment transport potential at
Frying Pan Shoals, North Carolina
4 March 2021
Page - 6 - of 6

transport potential, suggest that deposition onto Frying Pan Shoals may predominantly be
sourced from East Beach.

Figure 4: Gross annual sediment transport potential computed by the UNIBEST model.

VBHI Frying Pan Shoals Nourishment Project
Biological Monitoring Plan (March 2021) 1 | Page
Village of Bald Head Island Frying Pan Shoals Beach Nourishment Project
Biological Monitoring Plan
(March 30, 2021)
Background
Benthic fauna are often utilized as a potential indicator of biological health in marine/estuarine
communities – particularly in response to natural or human-induced perturbations. Characteristics
of benthic infauna or epi-fauna that make them particularly well-suited for such studies include: (1)
low motility; (2) close association with sediment substrates; and (3) importance in transfer of
energy to higher trophic levels (Alphin 2009). As the frequency of federal and non-federal beach
nourishment projects have increased, there has been a greater level of focus on evaluating the
degree of impact of these projects on the biological communities at both the borrow site and the
nourishment site. Prior studies have focused principally on the macroinvertebrate population
recovery of the nourished beachfront. The results of these studies have varied widely due to a
number of influencing factors. In general, it has been demonstrated that there is an abrupt decline
in benthic populations immediately following nourishment due to physical burial and/or
displacement. Recovery may then occur over a period of months to one year depending on the
degree of sediment matching of the fill material relative to the native beach (Van Dolah et al. 1994;
Jutte et al. 1999; Berquist 2008).
Less information is available regarding the biological recovery of the borrow site. Benthic
regeneration in these areas will be influenced by the following: (1) the composition of the surficial
sediments left in place post-excavation; (2) the physical recovery or rate of infilling of the site; (3)
the water quality overlying the sediment interface; and (4) the proximity of intact populations
available for recolonization of the excavated area.
The following monitoring plan provides methodology for determining the response and recovery of
benthic populations at the subtidal borrow site. It employs a Before-After Control-Impact (BACI)
design in order to document changes of the project areas to relatively undisturbed reference areas
(Berquist 2008). Both the impact and the reference areas are sampled multiple times both pre- and
post-construction in order to evaluate the immediate response of the benthos and the longer-term
recovery of these populations.
Benthic Monitoring of Borrow Site
In an effort to document the impacts on, and recovery of, benthic infaunal communities and
sediment characteristics in the sand borrow area, pre- and post-construction sampling of benthos
will be conducted. The pre-construction sampling events will occur on a seasonal basis (with a
minimum of 4 pre-project sampling events corresponding to each season).
ATTACHMENT C.
VBHI Frying Pan Shoals Nourishment Project
Biological Monitoring Plan (March 2021) 2 | Page
Benthic invertebrates populations will be sampled using a “petite” ponar grab at representative
locations along four (4) transect lines across the portion of the shoal to be dredged (refer to Figure
1). Four (4) sampling locations (with two replicates at each location) will be collected and
transported to a qualified laboratory for fixation. The total number of samples to be collected at
the dredge site will be thirty-six (32). At each sampling location, one additional ponar grab will be
collected and transported to a qualified laboratory for particle size analysis to characterize
sediment content.

Additional samples will be collected along representative subtidal areas of Frying Pan Shoals
(outside of the proposed dredge footprint) for control/reference sites. The reference areas consist
of 3 transects. Each transect will consist of 4 sampling locations (refer to Figure 1). Two (2)
replicates will be collected at each location. The total number of reference samples to be collected
will be twenty-four (24). At each sampling location, one additional ponar grab will be collected and
transported to a qualified laboratory for particle size analysis to characterize sediment content.

All benthic samples will be fixed in 10% buffered formalin (formaldehyde derivative) solution with
rose Bengal dye added and later transferred to a 70% isoproponol preservative for storage. All
three replicates will be sorted and identified to the lowest taxonomic level possible (generally
species) and counted. Species list and mean abundances will be compiled. Additional statistical
analyses may be performed for species richness and diversity. Diversity will be calculated using the
Shannon Weiner Diversity Index.

Post-construction monitoring will occur on an annual basis with Year 0 sampling to occur
immediately post-dredge. Year 1 monitoring will be performed one year subsequent to the dredge
event. Monitoring will continue to occur through Year 3 (post-dredge). Annual monitoring reports
will document the results and findings of the benthic monitoring. Reports will be submitted to the
U.S. Army Corps of Engineers and to the North Carolina Division of Coastal Management each year.

VBHI Frying Pan Shoals Nourishment Project
Biological Monitoring Plan (March 2021) 3 | Page
Literature Cited:

Alphin, T.D. 2009. Benthic Faunal Communities associated with the Mason Inlet Relocation Project
Year 6 Post-Construction (December 2007) - Summary of Findings. Unpublished Report. 26 pp.

Berquist, et al. 2008. Change and Recovery of Physical and Biological Characteristics at Beach and
Borrow Areas Impacted by the 2005 Folly Beach Renourishment Project. SC. Technical Report No.
102. Prepared by the Marine Resources Division, South Carolina Department of Natural Resources,
Charleston, SC for the US Army Corps of Engineers, Charleston District. 112 pp.

Jutte, P.C. and R.F. Van Dolah. 1999. An assessment of benthic infaunal assemblages and sediments
in the Joiner Bank and Gaskin Banks borrow areas for the Hilton Head Beach Renourishment
Project. Final Report – Year 1. Prepared by the Marine Resources Division, South Carolina
Department of Natural Resources for Olsen Associates, Inc. and the Town of Hilton Head Island.

Van Dolah, R.F et al. 1994. Environmental evaluation of the Folly Beach Nourishment Project. Final
Report. Prepared by the Marine Resources Division, South Carolina Department of Natural
Resources, Charleston, SC for the US Army Corps of Engineers, Charleston District. 155 pp.

0 0.5 1.0 2.0
L:\CAMA\2019 CAMA FILES\LMG19.239 --- Frying Pan Shoals Dredging, Jeff Griffin\CAMA\Sand Source Permit Figure.dwg
Frying Pan Shoals
Sand Source Area
Base map is NOAA navigation chart 11537 obtained from
www.charts.noaa.gov (ENC chart US5NC12M).
Note: This is not an engineered or surveyed drawing. This drawing is intended
to show the approximate locations of proposed benthic sampling locations and is
not intended to depict specific borrow area limits. Refer to permit drawings for more
detailed information.
Applicant/Project:
Title:
Benthic
Monitoring GSF
Drawn By:
Date:
Scale:
1"=1 Nautical Mile
Job Number:
Figure:
Revision Date:
LMG19.239
NA
3805 Wrightsville Ave, Suite 15
Wilmington, North Carolina 28402
Telephone: [phone]
Village of Bald Head Island/
South Beach
Resourishment Project
2/15/2020
1
Legend
Reference Transect
and Sample Location
Sand Source Area Transect
and Sample Location