Oak Island 2020_2021_Temperature Monitoring Report_02092022 v3

moffatt & nichol
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I Mir) Oak Island
Oak Island
Nourishment Project
2020/2021
Temperature Monitoring
Report
Prepared for: Town of Oak Island

Table of Contents
1. Project Background.....................................................................................................................................1
2. Sand Monitoring..........................................................................................................................................1
2.1 Temperature Monitoring...................................................................................................................3
2.2 Sand Color Monitoring......................................................................................................................5
2.3 Temperature Results...........................................................................................................................5
2.4 Sand Color Results..............................................................................................................................8
3. Conclusions..................................................................................................................................................9
4. References.....................................................................................................................................................9
List of Figures
Figure 1. Oak Island Renourishment Project Extends..................................................................................2
Figure 2. Station Locations for Sand Temperature and Color Monitoring ............................................... 4
Figure 3. Temperature Logger Installation Process....................................................................................... 5
Figure 4. Restoration Monitoring Station Temperature Results..................................................................7
Figure 5. Control Monitoring Station Temperature Results.........................................................................8
List of Tables
Table 1. Temperature Monitoring Station Temperature Summary.............................................................6
Table 2. Control Monitoring Station Temperature Summary......................................................................6
Table 3. Immediate Post Construction Munsell Colors................................................................................8
Table 4. Temperature Monitoring Station Munsell Color Results..............................................................8
Appendices
Appendix A — Oak Island Sea Turtle Nesting Data
Appendix B — Temperature Logger Installation Summary
Appendix C — Temperature and Munsell Log
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page ii

1. PROJECT BACKGROUND
The Town of Oak Island (Town), located in Brunswick County North Carolina, constructed a beach
nourishment project to mitigate oceanfront erosion from Hurricane Matthew which made landfall on
October 8, 2016. Project construction began on April 8, 2021, and was completed on May 22, 2021
(44 days) by Great Lakes Dredge and Dock Company Inc. (GLDD).
Moffatt & Nichol (M&N) served as the engineer on behalf of the Town of Oak Island (Town). Jay
Bird Shoals was the offshore borrow area utilized. The project placed a total of approximately 729,000
cubic yards (cy) along 17,000 feet (ft) (approximately 3.2 miles) from SE 63rd Street to 3rd Place East.
Figure 1 shows the beach fill extent for the project.
2. SAND MONITORING
Immediately post -construction of the nourishment project, the US Fish & Wildlife Service (FWS)
expressed concerns that darker sediment could potentially retain more heat compared to lighter
sediment. This could possibly affect sea turtle nesting and hatchling success by influencing gender,
which is governed by the incubation temperature. Although no documented state or federal criteria
for sediment color exist, FWS recommended a minimum Munsell color value of 5 for the Oak Island
nourishment project after sand color issues with the borrow site arose. To help address these concerns,
the Town agreed to participate in post -construction monitoring, conducted by Moffatt & Nichol, of
sand temperature and color from June 30, 2021, through September 30, 2021, as recommended by
FWS.
In addition, throughout the nesting season all nests that were laid in dune restoration areas were to be
relocated by the Oak Island Sea Turtle Protection Program to areas that did not receive sand. For the
2021 nesting season, a total of 20 nests were laid within the nourishment area. Of those 20 nests, five
had to be relocated because they were laid in nourishment areas (Appendix A). Final nest emergence
day among the nests located within the nourishment area was September 22, 2021. The 2021 season
recorded 115 false crawls, 80 of which occurred in the nourishment areas.
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 1

Figure 1. Oak Island Renourishment Project Extends
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 2

WhIR
2.1 TEMPERATURE MONITORING
Sand temperatures were monitored by the Town from June 30, 2021, to September 30, 2021. HOBO
NM203 TidbiT waterproof temperature loggers, manufactured by the OnSet Corporation, equipped
with wireless data retrieval through Bluetooth technology were used to collect sand temperature data.
HOBO MX2203 provides temperature readings accurate within ±0.36°F. The data loggers were
placed in 5 locations within the nourishment areas and 2 locations outside of the nourishment area,
to be used as control locations (Figure 2). One control site was located east of the nourishment extent,
and the other control site was located on Caswell Beach which is to the east of Oak Island. The loggers
were attached to wooden stakes using duct tape and were installed at a depth of 18 inches from the
ground by burying the stakes perpendicular to the surface of the sand. The loggers were placed on the
dune depending on the width of the dune crest and steepness of the dune face to protect against
escarpment risk (Figure 3). All 7 locations coincided with color sampling locations and were approved
by FWS, NCWRC and the Oak Island sea turtle monitoring coordinator.
Data was set to record temperatures at 1-hour intervals. To facilitate equipment retrieval and prevent
disturbance during the monitoring, each logger was marked with stakes and construction flagging
similar to sea turtle nest markers. See Figure 3 below for a photo summary of the installation process,
for a complete installation summary see Appendix B.
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 3

Temperature Gage Location #5
11th PL E Beach Acces
Dodge Placement #1
,95
-Elev 12' NAVD88f-
000c =
(-20' up dune face)
_—
Temperature Gage Location #6
,Tempereture
N
6th PL E Beach Access
=
Gage Location �k4
Temperature Gage Location #3
Temperature Gage Location #2
Dodge Placement#2
00o
29th PI E Vehicle Access
SE 58th St. Beach Access
SE filth St Beach Access
Elev 17 NAVD88
Ohio Placement 02
Ohio Placement #1
_+
East of Placement Area
{-20' up dune face)
- Elev 12' NAVD88
- Elev ITNAVD88
- Elev ITNAVD88
up dune face)
{-20' up dune face)
_
Based on March 2021 Survey
L
'
O' N�G aE A C
T
P
Dodge Island
- -Ohio Placement
PlacementILI - "
T_
H q
Temperature Gage Location #7 a w — - _ _ "
5th PL West Beach Access A N
_ _- "4*. ' ..
T
C
..
West of Placement Area
Nearest High Ground ,
a w `-c ".
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r•.,,'..,.,.l.,.,.
Legend
■ OKI Temperature Logger Locations
Caswell Beach Survey Transects
aec„ iWN�rvy Q,flrv1U�M
OKI Survey Transects
A❑ Survey Boundary
❑ 1.5003,00o 6,W❑
Feet
Figure 2. Station Locations for Sand Temperature and Color Monitoring
Temperature Gage Lacatian 91
Caswell Beach Control Location m
425 Caswell Beach Rd.
- Elev 12' NAVD88
Based on March 2021 Survey
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 4

Figure 3. Temperature Logger Installation Process
During the monitoring period, loggers were downloaded at approximately two -week intervals using
the logger Bluetooth capability. This two -week interval allowed for timely identification of any issues
with the dataloggers such as: equipment problems or needing to relocate due to overwash or erosion.
Data spreadsheets were emailed to state and federal agency representatives every two weeks. During
the monitoring period a second temperature logger was installed at 5t1i PL West Beach Access on
August 2nd due to abnormality observed in the data recorded by the original data temperature logger
#7. Therefore, the data gathered before August 2nd at this location were omitted from analysis.
2.2 SAND COLOR MONITORING
Sand color was monitored on the same frequency as temperature monitoring (every two weeks).
During testing, the sediment color 6" from the surface at the seven temperature logger locations was
identified using the Munsell color chart as directed by the agencies.
2.3 TEMPERATURE RESULTS
Results for sand temperature at the 7 monitoring locations across Oak Island are presented in the
graphs and tables below with raw data provided in Appendix C. Graphs/tables displaying in red
indicate that the data was from a control station, while black graphs/tables indicate monitoring
locations within the nourishment project area. The pivotal temperature, the temperature that produces
50% of each sex, is 84.6 °F (Mrosovsky 1988), this is marked on the graphs by the dashed black line.
The thermal influence on sexual differentiation in sea turtle development occurs in the middle third
of egg incubation (Mrosovsky & Pieau 1991).
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 5

As shown in Table 1 below, the minimum temperature recorded within the nourishment project area
during the monitoring period occurred at 5th PI E and was measured as 76.0 'F. The maximum
temperature logged within the nourishment project area measured 92.5 °F, occurred at the 11th PI E
station location. As shown in Table 2, the minimum control station temperature observed was also
76.0 °F, which was measured at SE 67th Street. The maximum control station temperature detected
was 90.7 °F, observed at the Caswell Beach location. The difference between the control station
averaged means and the averaged means of the loggers within the nourishment area is 1.1 'F.
Table 1. Temperature Monitoring Station Temperature Summary
Temperature
58th PL E
29th PL E
11th PL E
6th PL E
5th PL W*
Avg
Mean
84.9
85.3
87.1
86.4
84.0
85.5
Min
77.3
77.5
79.8
79.1
76.0
77.9
Max
91.3
91.6
92.5
91.8
90.2
91.5
* Recording at this station begin on August 2
Table 2. Control Monitoring Station Temperature Summary
Temperature
SE 67th St
Caswell Beach
Avg
Mean
84.0
84.7
84.4
Min
76.0
76.7
76.4
Max
90.5
90.7
90.6
Each temperature monitoring station (including control stations) experienced periods above and
below the pivotal 84.6-degree Fahrenheit temperature referenced above (Figures 4-5). The average
temperature over the recording period for each station was above this pivotal temperature, except for
the 5' PI W location which had a shorter observation period due to issues with equipment (Table 2).
The control monitoring stations measured above 84.6 degrees Fahrenheit 43-55% of the monitoring
period, on average 49%. Sand temperatures in July - August were mainly above the pivotal mark. A
drop is observed in September as rainfall increases and temperatures recorded at local weather stations
decrease.
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 6

95
SE 58th St 29th PL E
95
90 90 yY
LL
i LD
7 a
i 85 E 85
0
£ E
So So
75 75
L 30-Jun 13-Jul 26Jul B-Aug 21-Aug 4-Sep 17-Sep 30-Sep 30-Jun 13-Jul 26-Jul 8-Aug 21-Aug 4-Sep 17-Sep 30-Sep
11th PL E 6th PL E
95 I 95
Sth PL W
95
90
E
a
E 85
m ---
a
m
r
so
75
0-Jun 13-Jul 26-Jul 8-Aug 21-Aug 4-Sep 17-Sep 30-Sep
Figure 4. Restoration Monitoring Station Temperature Results
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 7

95 Caswell Beach 95 SE 67th St
90
>w
A 85
'a
n
f
8o
75
Sep I I 30-Jun 13-Jul 26-Jul 8-Aug 21-Aug 4-Sep 17-Sep 30-Sep
Figure 5. Control Monitoring Station Temperature Results
2.4 SAND COLOR RESULTS
Table 3 presents the temperature colors at the temperature monitoring stations immediately after the
construction took place. Table 4 below shows a summary of Munsell color values from the
monitoring stations over the period of observation. Recall that a minimum Munsell color value of five
was recommended by the FWS. Most observations at the monitoring stations that received
nourishment were recorded at or below a Munsell color value of five. It is difficult to draw conclusions
from the variations in the Munsell values that were reported at a station from one reading to the next,
as the result is subjective to the person administering the assessment. For each station the fraction of
readings where a Munsell value of five or greater was reported is shown.
Table 3. Immediate Post Construction Munsell Colors
Condition
58th PL
29th PL
11th PL
6th PL
5th PL
E
E
E
E
W
Wet
4/1
4/1
4/1
3/1
NA
Dry
6/1
7/1
6/1
5/1
NA
Table 4. Temperature Monitoring Station Munsell Color Results
Date
58th
PL E
29th
PL E
11th
PL E
6th PL
E
5th PL
W
Caswell
Beach
SE
67th St
Conditions
6/29/2021
5/2
6/1
4/1
6/1
6/3
7/1
7/1
Sunny
7/13/2021
6/1
5/1
5/1
6/1
5/3
7/2
7/1
Sunny
8/2/2021
5/2
5/2
5/1
5/1
5/3
7/2
7/1
Sunny
8/20/2021
6/2
6/2
5/2
5/1
6/2
7/2
7/1
Sunny
9/2/2021
6/2
5/2
5/1
5/2
6/3
7/2
7/1
Sunny
9/16/2021
6/2
5/2
4/1
5/1
6/2
7/1
7/1
Sunny
9/30/2021
6/2
5/2
4/1
5/1
6/2
7/1
7/1
Sunny
Fraction
Munsell >=5
7/7
7/7
4/7
7/7
7/7
7/7
7/7
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 8

3. CONCLUSIONS
Based on the data measurements, the temperature loggers in restored dune areas were slightly warmer
than temperatures in non -nourished areas. Shamblott et al., 2021 investigated the influence of beach
nourishment influences on thermal properties of eight North Carolina nourished beaches and
observed a temperature increase, on average, 0.62 OF (range 0.54 — 1.44 OF). With an average mean
temperature change of 1.1 OF, the temperature change observed in this project is higher than average
but is within the observed range.
The Munsell color data shows that the nourished sand values were lower than non -nourished areas.
Overall, the study and the results support the FWS concern that darker sediment could potentially
retain more heat compared to lighter sediment. However, it should be remembered that all nests that
were laid in the dune restoration project area were relocated to non -project areas so that any potential
project effects could be minimized.
4. REFERENCES
Mrosovsky, N. (1988) Pivotal temperatures for loggerhead turtles (Caretta caretta) from northern and
southern nesting beaches. Canadian Journal of Zoology 66: 661-669.
Mrosovsky, N., Pieau, C. (1991) Transitional range of temperature, pivotal temperatures and
thermosensitive stages for sex determination in reptiles. Amphibia-Reptilia 12: 169-179.
Shamblott, K., Reneker, J.L., Kamel, S J. (2021) The thermal impacts of beach nourishment across a
regionally important loggerhead sea turtle (Caretta caretta) rookery. Ecosphere 12(3):e03396
Oak Island Nourishment Project 2020/2021 1 Temperature Monitoring Report) Page 9