Caswell_Monitoring_2022_FINAL

4700 Falls of Neuse Rd, Suite 300
WhARaleigh, NC 27609
[phone]
m o f f a t t & n l c h o l www.moffattnichol.com
MEMORANDUM
To: Heather Coats (DCM), Greg Currey (USACE)
From: Brandon Grant (MN)
Cc: David Kelly (OI), Johnny Martin (MN), Sam Morrison (MN), Mark Pirrello (MN)
Date: October 6, 2022
Subject: 202112022 Oak Island Nourishment Project: Post -Construction Shoreline Survey
Summary 2022
M&N Job No.: 10128-08
The special conditions of CAMA Permit No. 31-20 (Condition #8) and SAW-2018-02230 (Special Condition
#43) required the Town of Oak Island (Town) conduct a post -construction shoreline survey of Caswell
Beach as defined in the Shoreline Monitoring Plan dated January 30, 2020 and the associated amendment
letter dated February 24, 2020.
Survey Data Sources
The most recent shoreline survey was conducted by TI Coastal on May 16-25, 2022 between Stations (Sta.)
20+00 and Sta. 200+00 on Caswell Beach (see Figure 1). A summary of all survey efforts associated with
the monitoring plan to date are shown in Table 1.
Figure 1. Caswell Beach Monitoring Transects
Table 1. Monitoring Plan: Survey History
Location
Survey Date
Source
Extent
Caswell Beach
March 16-23, 2021
TI Coastal
Sta. 20+00 — Sta. 200+00 10+00 spacing)
Caswell Beach
October 6-8, 2021
TI Coastal
Sta. 20+00 — Sta. 200+00 10+00 spacing)
Caswell Beach
May 16-25, 2021
TI Coastal
Sta. 20+00 — Sta. 200+00 10+00 spacing)
1

M&N # 10128-08
October 6, 2022 Memorandum
The annual shoreline monitoring survey in March 2021 was performed prior the permitted beach
nourishment projects for Oak Island and is considered the baseline survey.
The October 2021 survey was performed at the request of Caswell Beach (CB) following a telephone
conversation with Moffatt & Nichol (MN) on October 4, 2021, with CB noting their concerns of escarpments
forming in the vicinity of the Oak Island Lighthouse - 300 block of Caswell Beach Rd at approximately
Station 80+00. The assessment of the October survey data performed by MN did not identify shoreline
trends that would indicate that dredging of Jay Bird Shoals has negatively affected the shoreline in
comparison to baseline conditions at the hotspot or the overall Caswell Beach Oceanfront shoreline. Since
Station 80+00 shoreline condition is a dynamic area as noted by CB prior to the OI projects, it will continue
to be evaluated in detail in subsequent annual monitoring assessments. Survey data was also collected
along Caswell Beach on May 26, 2022, which is the first survey after the completion (April 2022) of the two
Oak Island nourishment projects utilizing Jay Bird Shoals as the borrow source. The final volume removed
from Jay Bird Shoals from these two projects combined is approximately 2 million cubic yards (Mcy). Future
surveys will be performed along Caswell Beach in Spring 2023, Spring 2024, and Spring 2025 as required
by the special conditions of the permit. The analysis is being completed using the same methodology as
discussed with the Town of Caswell Beach's Engineer, Coastal Protection Engineering (CPE), to maintain
consistency in assessment methodology.
Discussion of Shoreline and Volume Trends
The shoreline and volume change calculations were performed in accordance with the monitoring protocol
defined in Appendix G of the major modification to CAMA Permit 31-20. Shoreline change at mean high
water (MHW) and volume change above -3.1 ft NAVD88 and depth of closure (DOC) were calculated
between the March 2021 and May 2022 surveys. MHW for Caswell Beach is +1.8 ft NAVD88 (+2.9 ft
NGVD29) and the DOC elevation selected is -15 ft NAVD88 (-13.9 ft NGVD29).
Three reaches have been developed to assess shoreline changes in the Caswell Beach shoreline: Fort
Caswell — Inlet (Sta. 20+00 — Sta. 50+00), Caswell — East (Sta. 60+00 — Sta. 150+00), and Caswell — West
(Sta. 160+00 — Sta. 200+00). The overall Caswell Oceanfront includes Caswell — East and Caswell — West.
The divide between East and West was based on shoal influence within the East reach and the distinct
separation in infrastructure development between East and West reaches. The Caswell — Oceanfront spans
from Sta. 60+00 to Sta. 200+00. The overall summary of shoreline and volume change is shown in Table
2. The Caswell — Oceanfront experienced overall recession of the MHW shoreline and volumetric accretion
above -3.1 ft NAVD88 and DOC. Within each reach, volume change varied between accretion and erosion
for Caswell — East and Caswell — West above -3.1 ft NAVD88 respectively. The overall erosion experienced
in Caswell — West above -3.1 ft NAVD88 was minor and recovered above the DOC. The erosion
experienced within the Fort Caswell — Inlet section is typical of a highly dynamic inlet system.
Table 2. Shoreline Change and Volume Change Summary
Avg.
Cumulative
Avg
Cumulative
March 2021 - May2022
Reach
Shoreline
Avg Volume
Volume
Volume
Volume
(Total Change)
Length
Change @
Change above
Change above
Change
Change above
MHW (+1.8 ft
-3.1 ft NAVD88
_3.1 ft NAVD88
above
DOC
NAVD88
DOC
Reach
ft
ft
c /ft
cy
c /ft
c
Fort Caswell — Inlet
3,502
-29.6
-9.2
-32,046
-16.8
-59,010
Sta. 20+00 — Sta. 50+00
Caswell — East
10,031
-2.2
2.9
28,999
13.9
139,658
Sta. 60+00 — Sta. 150+00
Caswell — West
4,589
-16.0
-0.4
-1,992
5.7
26,037
Sta. 160+00 — Sta. 200+00
Reach
weighted avg
weighted avg
total
weighted
total
Length
av
Caswell
18,122
-11.0
-0.3
-5,039
5.9
106,685
Sta. 20+00 — Sta. 200+00
Caswell — Oceanfront
14,620
-6.5
1.8
27,007
11.3
165,694
Sta. 60+00 — Sta. 200+00

M&N # 10128-08
October 6, 2022 Memorandum
The calculated shoreline and volumes change for each profile is shown in Figure 2 and Figure 3,
respectively. The shoreline and volume change trends were also shown within the Oak Island — East End
reach for comparison for a region that is a significant distance from the Jay Bird Shoals borrow area and
was not nourished during the two recent OI Nourishment Projects. The shoreline change oscillates between
erosion and accretion across Caswell — East with an average reach trend of mild recession of the MHW
shoreline position. However, the volume change within this reach consistently indicates that material was
gained above -3.1 ft NAVD88 and DOC in comparison to the baseline survey. Sta.80+00 hotspot also
showed similar trends of minimal shoreline change and volume change above -3.1 ft NAVD88 and volume
gain above DOC. Shoreline change at MHW within Caswell — West shows an increase in erosion; however,
volume loss was minimal at -3.1 ft NAVD88 and material was gained above DOC. The Oak Island — East
End also showed these same trends of increased MHW line recession and overall volumetric gain above
the DOC elevation of -15 ft NAVD88. These trends indicate that material from higher elevations is being
pulled to lower elevations along the profile and is remaining within the system. This trend noted in both
Caswell — East and Caswell — West is highlighted by the profile plots shown in Attachment A, where material
from the upper beach has migrated down the profile, flattening the nearshore slope and building up the
nearshore bar. The bar has been built up and has migrated slightly offshore. Another trend observed from
the profile plots; but not captured in the volume change analysis, was an increase in frontal dune width
and/or elevation in areas where wider dry berms are present. This accretion is a nature process due to the
aeolian transport of material from the berm to the dune increasing the protection these dunes provide and
may be a contributing to observed shoreline recession in these reaches.
Caswell Beach: Shoreline Change March 2021 - May 2022
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Station
Shoreline Change MHW
Figure 2. Caswell Beach Shoreline Change
3

October 6, 2022
M&N # 10128-08
Memorandum
Caswell Beach: Volume Change March 2021 - May 2022
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Station
Volume Change Above -3.1 ft NAVD88 —Volume Change Above DOC
Figure 3. Caswell Beach Volume Change
Historical Analysis
The Town was also required to evaluate the available historical datasets along Caswell Beach. Survey data
along Caswell Beach was available from August 2000 onward, collected by the United States Army Corps
of Engineers (USACE) or the Town though engagement with TI Coastal. Discrete timeframes were selected
to bracket the effects of beach nourishment from the Wilmington Harbor Maintenance Dredging projects
and relevant storms. Data prior to, and directly after the 2001 Wilmington Harbor Deepening Project, were
removed from the historical analysis, and the starting date of the historical evaluation was February 2003.
Two sets of graphs are presented below. The first set (Figure 4 — Figure 6) includes all available data
between 2003 and 2021 and includes storm events and Wilmington Harbor Maintenance Dredge Projects.
The second set (Figure 7 — Figure 9) encompasses the same timeseries; however, removes data
associated with the 2009 and 2018 Wilmington Harbor Maintenance Projects. Hurricanes Matthew and
Florence in 2016 and 2018, respectively, were also removed from the historical analysis due to surveys not
being available to separate the hurricane effects from the beach placement effects. The mean change and
standard deviations were calculated for MHW shoreline and volume changes above -3.1 ft NAVD88 (-2 ft
NGVD) and DOC and plotted with respect to the annualized results from the most recent survey from March
2021 to May 2022 as shown in each set of figures. If the average calculated values over any three adjacent
beach profile survey transects (covering a 3,000 ft section of shoreline) exceeds the mean values by +/-
one standard deviation, the Town will convene a Technical Advisory Committee (TAC) consisting of three
coastal engineers registered in the State of North Carolina, (1 — Oak Island, 1 — Caswell Beach, 1 —
Independent) to review the measured MHW shoreline and volume changes and investigate potential
causes. The TAC will determine if a cause determination for the exceedance can be made or if additional
monitoring is required. Based on surveys collected to date and the subsequent assessments, the criteria
for the formation of a TAC has not been met in either case.

October 6, 2022
M&N # 10128-08
Memorandum
Historic Shoreline Change: All Data
80
60
40
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1
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1
Figure 4. Caswell Beach: Historical MHW Shoreline Change (All Data)
Historic Volume Change Above -3.1
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50
40
30
20
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wellaiIn
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Station
—Mean Volume Change (2003-2021) --*—Spring 2021 -Spring 2022 Annualized Volume Change
Figure 5. Caswell Beach: Historical Volume Change Above -3.1 ft NAVD88 (All Data)
5
Figure 5. Caswell Beach: Historical Volume Change Above -3.1 ft NAVD88 (All Data)
5

October 6, 2022
M&N # 10128-08
Memorandum
Historic Volume Change Above DOC: All Data
60
50
40
30
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I
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Figure 6. Caswell Beach: Historical Volume Change Above Depth of Closure (All Data)
Historic Shoreline Change: Excluding Nourishment Events
100
80
60
40
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1
1
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Figure 7. Caswell Beach: Historical MHW Shoreline Change (No Nourishment)

October 6, 2022
Historic Volume Change Above -3.1 ft NAVD88: Excluding Nourishment Events
60 I I
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Station
—Mean Volume Change (2003-2021) --*—Spring 2021 - Spring 2022 Annualized Volume Change
M&N # 10128-08
Memorandum
Figure 8. Caswell Beach: Historical Volume Change Above -3.1 ft NAVD88 (No Nourishment)
Historic Volume Change Above DOC: Excluding Nourishment Events
60
50
40
30
20
0
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10
0
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-20
-30
-40
-50Caswell-West Caswell -East Fort
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Station
—Mean Volume Change (2003-2021) --*--Spring 2021 - Spring 2022 Annualized Volume Change
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Figure 9. Caswell Beach: Historical Volume Change Above Depth of Closure (No Nourishment)
7

October 6, 2022
M&N # 10128-08
Memorandum
Summary
With the completion of the 2021/2022 OI nourishment projects and dredging of Jay Bird Shoals in April
2022, the Caswell Beach — Oceanfront has experienced minor recession of the MHW shoreline and a
volume increase above the -3.1 ft NAVD88 and DOC reference elevations along the surveyed area in
comparison to the baseline conditions. These results indicate that the OI projects have not negatively
affected the available sediment volume on Caswell Beach between March 2021 and May 2022. While
shoreline recession and volumetric loss was measured along the inlet, these dynamic areas are more
susceptible to shoreline change and erosion on a continual basis. Shoreline surveys and monitoring will
continue to be performed per permit conditions to document changes in the Caswell Beach shoreline.
Enclosures:
Appendix A: Caswell Beach Profile Plots
A