20141307 Ver 1_Appendix F Eastern Channel Project Update Memo_20141218

APPENDIX F
EASTERN CHANNEL PROJECT UPDATE MEMO
(SENT VIA EMAIL 24 OCTOBER 2014)

1616 East Millbrook Road, Suite 160
„11 Raleigh, NC 27609
(919) 781- 4626Fax [phone]
m o f f a f t & n i c h o l www.moffattnichol.com
MEMORANDUM
To: Attendees of August 27th, 2014 Agency Meeting
From: Moffatt & Nichol
Date: October 24, 2014
Subject: Phase I of the Lockwood Folly Habitat Restoration Project — Eastern Channel
Proposed Alignment
M &N Job No.:
The purpose of this memorandum is to (a) present a summary of findings of the ongoing additional
investigations in support of the Phase I of the Lockwood Folly Habitat Restoration Project, the proposed
dredging of Eastern Channel at Lockwoods Folly Inlet; and (b) identify a proposed alignment for the
Eastern Channel for environmental agency consideration and comment. This memo is a follow up to the
interagency pre - scoping meeting held August 27, 2014 (Attached for review are draft notes from the
Interagency Meeting— Appendix A).
As expressed at the Interagency Meeting, the Town has an urgent need to conduct the proposed
project this winter. In order to expedite the project it is requested that a review be provided of the
proposed channel alignment and any comments /concerns be provided to Moffatt & Nichol within one
week of receipt of this document (by October 31, 2014). The Town will take those comments into
consideration as it must proceed with design, permitting and preparation of construction documents
starting the week of November 3.
Background
As discussed at the interagency pre - scoping meeting held August 27, 2014, the purpose and need for the
project is driven by navigation, water quality, infrastructure projection and habitat loss. The navigation
of Eastern Channel, a natural channel, is limited to high tides and many areas within the channel have
severely shoaled to -4' to -6' NAVD. Currently, the connection of Eastern Channel at Lockwoods Folly
Inlet is closed due to the migration of large sand shoal /spit. Water quality has been a concern of the
Town of Oak Island for some time now as nutrient and fecal levels have spiked in Davis Creek, a tributary
of Eastern Channel. There are also a number of vulnerable homes along the west end of Oak Island as
2013 -2014 winter storms have exacerbated the erosion conditions of the western shoreline;
subsequent to the scoping meeting this area has realized additional erosion and there are a series of
escarpments fronting the reach of shoreline which limit sea turtle nesting habitat.

Review of Proposed Action & Alternatives
As discussed at the pre - scoping meeting the proposed action consists of dredging a new channel with
placement of compatible material on the beach at the West end of the Town and placement of non -
beach compatible material in the upland disposal area at Sheeps Island. Three potential channel
alignments were identified as illustrated in Figure 1. Considerations and potential tradeoffs with
respect to alignment that were discussed at the meeting included: channel stability /maintenance
dredging requirements, sediment quality /compatibility with native beach material and quantity.
LOCkuvoadFl
EC-
Legend
O Eastern Chann el WiN—re Locations
2014
Channel Alignment Option 7
Channel Alignment Option 2
f
- -
EC-
Figure 1: Eastern Channel Proposed Alignment Options and Vibracore Locations
All channel options are proposed to be dredged approximately 50 -100 feet wide with an average depth
of dredging ranging from 3 - 11 feet deep on a 3:1 slope. At typical proposed section is illustrated in
Figure 2.
1d,14 2
Legend
O Eastern Chann el WiN—re Locations
2014
Channel Alignment Option 7
Channel Alignment Option 2
N
- -
ChannelAlignmentOpl -3
u- e
Aerial Imagery Date 2012
S
0 450 990
1,800
Feel
Figure 1: Eastern Channel Proposed Alignment Options and Vibracore Locations
All channel options are proposed to be dredged approximately 50 -100 feet wide with an average depth
of dredging ranging from 3 - 11 feet deep on a 3:1 slope. At typical proposed section is illustrated in
Figure 2.
1d,14 2

DREDGE ALIGNMENT
590' 54. a'
EXISTING EXIST, EL -2.0±
RATHYMETRY - // I Al. DEPTH
I_— ------------- I!___-- _______� _ ____. ----- —_
DREDGE. ELI -15.0
TYPICAL SECTION CN
STA 83 +00 TO 100 +00
Figure 2. Typical Cross - Section of Proposed Channel at Station 90 +00 for Option 2
A summary of the considerations identified at the pre - scoping meeting is provided in Table 1.
Table 1. Summary of Considerations with Respect to Channel Alignment
1„14
Estimated Dredge
Potential
Channel
Quantities (cy)
intertidal
Channel Alignment
Stability /Maintenance
Water
Requirements
Beach
Estimated
subt idal
Quality
Compatible
Incompatible
Impact
Benefits
(acres)
Uncertain — likely most
Increased
Option 1- adjacent to
stable — least
204,000
34,000
21.98
flushing
Sheeps Island
maintenance
Option 2 - northwest
Uncertain — likely
Increased
through inlet flood
stable — mid-
194,000
34,000
22.76
flushing
shoal
maintenance
Expect more rapid
Option 3 - parallel
shoaling than 1 or 2 —
Increased
and adjacent to north
Least stable — most
184,000
34,000
22.07
flushing
shore of Oak Island
maintenance
1„14

Sediment Compatibility
DCM Sediment Criteria Classification
The native sediment distribution for Oak Island is defined based on the percent gravel, granular
sediment, sand, fine - grained sediment, and calcium carbonate present in samples taken from thirteen
locations along a specific transect (see Figure 2). These thirteen samples were then averaged to obtain a
composite average for that transect. Five transects were sampled along the Oak Island shoreline where
sand is proposed to be placed. The composite average for each of the five transect were then averaged
to obtain a grand mean for the native beach. North Carolina Division of Coastal Management (NCDCM)
has set requirements for gravel, granular sediment, fine - grained sediment, and calcium carbonate,
which the borrow material cannot exceed (Table 2). The average percentage by weight of gravel in the
borrow site may not exceed the native grand mean of the gravel plus 5 percent. The average
percentage by weight of granular sediment in the borrow site may not exceed the native grand mean of
the granular sediment plus 10 percent. The average percentage by weight of fine - grained sediment in
the borrow site may not exceed the native grand mean of the fine - grained sediment plus 5 percent. The
average percentage by weight of calcium carbonate in the borrow site may not exceed the native grand
mean of the calcium carbonate plus 15 percent.
Figure 2: Locations of Native Beach Samples
1111 4

Table 2: Native Sediment Characterization and NCDCM Rule
The summary of the native sediment statistics including the mean, median, and standard deviation was
found (Table 3). The native material is characterized as a fine sand under the American Society for
Testing and Materials (ASTM) Unified Soil Classification System with a mean grain size of 0.28 mm.
These statistics were found in both metric units and phi units.
Table 3: Native Sediment Statistics
Native Global
Mean
NCDCM
Maximum
G rave 1
0.36%
5.36%
Granular
0.67%
10.67%
Sand
98.18%
NA
Fines
0.79%
5.79%
Carbonate
8.17%
23.17%
The summary of the native sediment statistics including the mean, median, and standard deviation was
found (Table 3). The native material is characterized as a fine sand under the American Society for
Testing and Materials (ASTM) Unified Soil Classification System with a mean grain size of 0.28 mm.
These statistics were found in both metric units and phi units.
Table 3: Native Sediment Statistics
MIA
Native Global
Mean
Median (mm)
0.27
Median ((p)
1.86
Mean (mm)
0.28
Mean (4))
1.82
Standard
Deviation (a (o)
0.78
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+ f�
`t S
.Z— 11 OEM "71 "Man Warr.
!'ti!* �
Legend
y�..r ��,.- •ors. r/�ar r�/R`
M y�
1
i•
— Chan no] Alignmeirit Option
+
A�rial 1—gory Date- 1
Q 200 400 No
Figure 3: Eastern Channel Alignment Options Detail
Sediment Characteristics of Borrow Site
The vibracores were split in to segments which include the main channel and the three proposed
options. The main channel includes vibracores 1 through 11 (see Figure 1). Option 1 includes vibracores
12 through 15 (see Figure 3). Option 2 includes vibracores 12, 17, and 18. Option 3 includes vibracores
12, 16, 19, and 20. The summary of the vibracore data shown on the next few pages is based on the
proposed dredge elevations. Vibracores 1 through 8, 21, and 22 extend to -9 ft NAVD88. Vibracore 9 is
located in the transition zone from -13 ft NAVD88 to -15 ft NAVD88; therefore, the dredge elevation was
set to the average value of -14 ft NAVD88. Vibracores 10 through 20 extend to -15 ft NAVD88.
Sediment characteristics of each vibracore were weighted averaged from the tip of the vibracore down
to the dredge elevation at the specific location (Table 4 -Table 7). Sediment statistics of each vibracore
were averaged using the same method (Table 8 -Table 11). Any results in the following tables not
meeting the individual criteria are shown in red.
1ld„ 6

Table 4: Sediment Characteristics of Vibracores 1 - 11
Note 1: Existing Channel Elevation Deeper than Dredge Elevation
Table 5: Sediment Characteristics for Eastern Channel Alignment Option 1
Option 1
Native Global
Mean
NCDCM
Maximum
EC -14-01
EC -14-02
EC -14-03
EC -14-04
EC -14-05
EC -14-06
EC -14 -21
EC -14-07
EC -14-22
EC -14 -08
EC -14 -09
EC -14 -10
EC -14 -11
Gravel
0.36%
5.45/.
0.70%
0.00%
0.001/.
See Note 1
1.45%
3.88%
0.00%
0.00%
0.03%
0.46%
132%
1.84%
13.28%
Granular
0.67%
10.7%
0.17%
0.03%
0.02%
1.38%
0.95%
0.04%
0.10%
0.11%
0.18%
1.06%
3.53%
5.26%
Sand
98.18%
NA
94.16%
50.06%
5.62%
94.29%
85.21%
47.97%
97.13%
93.77%
98.34%
96.64%
93.48%
69.12%
Fines
0.79%
5.8%
4.97%
49.91%
94.36%
288%
9.95%
51.99%
2.77%
6.09%
1.01%
0.98%
1.15%
12.35%
Carbonate
8.17%
23.2%
5.70%
7.30%
14.50°/
9.05%
14.01%
6.50%
6.50%
6.45%
4.64%
9.55%
17.73%
34.75%
Median (mm)
0.27
NA
0.16
1 0.06
1 NA
0.27
0.20
NA
0.17
0.23
0.18
1 0.25
0.38
0.34
Mean (mm)
0.28
NA
0.16
NA
NA
0.29
0.24
NA
0.17
0.23
0.19
0.27
0.42
NA
Note 1: Existing Channel Elevation Deeper than Dredge Elevation
Table 5: Sediment Characteristics for Eastern Channel Alignment Option 1
Option 1
Native Global
Mean
NCDCM
Maximum
EC -14-12
EC -14-13
EC -14-14
EC -14-15
Average
(12,13,14,15)
Gravel
0.36%
5.36%
1.46%
2.80%
7.55%
9.90%
5.43%
Granular
0.67%
10.67%
1.41%
1.35%
3.39%
2.98%
2.28%
Sand
98.18%
NA
96.45%
84.68%
85.81%
62.39%
82.33%
Fines
1 0.79%
1 5.79%
1 0.67%
1 11.18%
1 3.25%
1 24.72%
1 9.96%
Carbonate
8.17%
23.17%
12.24%
8.49%
19.47%
22.93%
1 15.78%
Median (mm)
0.27
NA
0.26
1
0.22
0.33
0.19
0.25
Mean (mm)
0.28
NA
0.28
NA
0.47
NA
NA
Table 6: Sediment Characteristics for Eastern Channel Alignment Option 2
Option 2
Native Global
Mean
NCDCM
Maximum
EC -14 -12
EC -14-17
EC -14-18
Average
(12,17,18)
Gravel
0.36%
5.36%
1.46%
5.77%
6.31%
4.51%
Granular
0.67%
10.67%
1.41%
2.33%
4.27%
2.67%
Sand
98.18%
NA
96.45%
90.04%
88.76%
91.75%
Fines
0.79%
5.79%
0.67%
1.85%
0.66%
1.06%
Carbonate
8.17%
23.17%
12.24%
15.66%
22.27%
16.72%
Median (mm)
0.27
NA
0.26
0.34
0.45
0.35
Mean (mm)
0.28
NA
0.28
0.42
0.56
0.42
Table 7: Sediment Characteristics for Eastern Channel Alignment Option 3
Option 3
Native Global
Mean
NCDCM
Maximum
EC -14 -12
EC -14-16
EC -14-19
EC -14-20
Average
(12,16,19,20)
Gravel
0.36%
5.36%
1.46%
4.23%
1.50%
3.15%
2.58%
Granular
0.67%
10.67%
1.41%
2.22%
1.75%
3.74%
2.28%
Sand
98.18%
NA
96.45%
92.80%
96.12%
92.56%
94.48%
Fines
1 0.79%
1 5.79%
1 0.67%
1 0.75%
1 0.64%
1 0.55%
0.65%
Carbonate
8.17%
23.17%
12.24%
15.66%
14.34%
19.31%
15.39%
Median (mm)
0.27
NA
0.26
1
0.34
0.29
0.43
0.33
Mean (mm)
0.28
NA
0.28
0.39
0.31
0.47
0.36
MIA

Table 8: Sediment Statistics for Vibracores 1 -11
Note 1: Existing Channel Elevation Deeperthan Dredge Elevation
Table 9: Sediment Statistics for Eastern Channel Alignment Option 1
Native Global
Average
Average
Option 1
EC -1412
EC -1412
EC 1413
EC -1414
EC -1415
Mean
Mean
EC -14-01
EC -14-02
EC -1403
EC -14-04
EC -14-05
EC -14-06
EC -14-21
EC -14-07
EC -1422
EC -1408
EC -1409
EC -14-10
EC -14-11
1.92
Mean
1.62
2.43
2.01
Mean (mm)
0.28
0.28
0.27
0.47
0.31
0.33
Mean (fl
1 1.82
1 1.83
Median (mm)
0.27
0.16
0.06
NA
See
Note 1
0.27
0.20
NA
0.17
0.23
0.18
0.25
0.38
0.34
Median (¢)
1.86
2.69
3.98
NA
1.86
2.32
NA
2.55
2.53
2.44
1.99
1.40
1.54
Mean (mm)
0.28
0.16
NA
NA
0.29
0.24
NA
0.17
0.23
0.19
0.27
0.42
NA
Mean ( (0)
1.82
2.66
NA
NA
1.77
2.07
NA
2.52
2.11
2.40
1.91
1.27
NA
Standard
Deviation (act)
1 0.78
0.76
NA
NA
1.03
1.61
NA
0.50
0.61
0.53
0.86
1.09
NA
Note 1: Existing Channel Elevation Deeperthan Dredge Elevation
Table 9: Sediment Statistics for Eastern Channel Alignment Option 1
Table 10: Sediment Statistics for Eastern Channel Alignment Option 2
Native Global
Average
Average
Option 1
EC -1412
EC -1412
EC 1413
EC -1414
EC -1415
Mean
Mean
( 12 17 18 )
Median (mm)
0.27
(12,13,14,15)
Median (mm)
0.27
0.26
0.22
0.33
0.19
0.25
Median ((P)
1.86
1.92
2.19
1.62
2.43
2.01
Mean (mm)
0.28
0.28
0.27
0.47
0.31
0.33
Mean (fl
1 1.82
1 1.83
1 1.90
1 1.09
1 1.69
1 1.59
Standard
0.92
1.50
1.55
1.32
Deviation (a4))
0.78
0.92
NA
1.89
NA
NA
Deviation (o (o)
Table 10: Sediment Statistics for Eastern Channel Alignment Option 2
Table 11: Sediment Statistics for Eastern Channel Alignment Option 3
Native Global
Average
Option 2
Option 3
EC -1412
EC -1417
EC -1418
EC -1420
Mean
Mean
( 12 17 18 )
Median (mm)
0.27
0.26
0.34
0.45
0.35
Median
1.86
1.92
1.54
1.14
1.50
Mean (mm)
0.28
0.28
0.42
0.56
0.42
Mean (4))
1.82
1.83
1.26
0.85
1.26
Standard
1.82
1.83
1.35
1.69
1.09
1.46
0.78
0.92
1.50
1.55
1.32
Deviation (a4))
0.78
0.92
1.24
Table 11: Sediment Statistics for Eastern Channel Alignment Option 3
Summary of Sediment Analysis and Compatibility
Overall based upon the above results, it would appear that along the main channel that the reaches
from vibracores 1, 2, 3, 4, 5, 6, 21 and 11 are not beach compatible and should be placed in Sheeps
Island. The reaches from vibracores 7, 22 (fines are <1% out of compliance - rounding), 8, 9, 10 are
beach compatible and should be placed on the beach.
1/,1
Native Global
Average
Option 3
EC -1412
EC -1416
EC -1419
EC -1420
Mean
(12,16,19,20)
Median (mm)
0.27
0.26
0.34
0.29
0.43
0.33
Median (c�)
1.86
1.92
1.54
1.80
1.22
1.59
Mean (mm)
0.28
0.28
0.39
0.31
0.47
0.36
Mean (4))
1.82
1.83
1.35
1.69
1.09
1.46
Standard
0.78
0.92
1.24
0.95
1.18
NA
Deviation (off)
Summary of Sediment Analysis and Compatibility
Overall based upon the above results, it would appear that along the main channel that the reaches
from vibracores 1, 2, 3, 4, 5, 6, 21 and 11 are not beach compatible and should be placed in Sheeps
Island. The reaches from vibracores 7, 22 (fines are <1% out of compliance - rounding), 8, 9, 10 are
beach compatible and should be placed on the beach.
1/,1

As for the options for the mouth of the Eastern Channel (see Figure 3), it would appear that Option 1
would be the least desirable as it is well out of compliance for % fines and just barely out of compliance
for %gravel (within 1 %). The material (median d= 0.25mm) is slightly finer than that of the native
material (median d= 0.27mm). Option 2 is next best with only two individual vibracores just barely out
of compliance with gravel (within 1%), but the average of all vibracores is within compliance. The
material (composite median d = 0.35 mm) is generally coarser than the native sand (median d= 0.27mm).
Option 3 is the best option from a beach compatibility perspective with all individual vibracores being in
compliance. The material (composite median d = 0.33 mm) is slightly coarser than the native sand
(median d= 0.27mm). However, this option (Option 3) is also the most likely to shoal in given its location
to the inlet and past behavior.
Channel Stability
As noted in the pre - application meeting, historically there has been significant migration and periodic
closing of the Eastern Channel. Qualitatively, the most stable alignment based on the location appears
to have been from 1978 (when a pilot channel was dredged) to the mid 1990s (CSE, 2009) when the
channel followed a more northwest alignment identified to be closer to Option 1 (adjacent to Sheeps
Island) or Option 2.
For a proposed channel to be relatively "stable ", theoretically it would be neither be dominantly
erosional nor depositional. The channel cross - sectional area and tidal discharge would allow for both (a)
adequate sediment transport capacity (to transport incoming sediments through the channel) and (b)
shear stress that does not exceed that which is allowable.
Coastal Science & Engineering (CSE, 2009) conducted field measurements of tidal water levels,
discharges, and current speeds at selected locations in the Lockwood's Folly inlet system, including the
main inlet channel, the Eastern Channel, and in the Atlantic Intracoastal Waterway (AIWW). From these
measurements, they reported the Eastern Channel maximum flood current velocity to be 2.3 ft /sec and
the maximum ebb current velocity to be 3.3 ft /sec. CSE (2009) reported the Lockwood's Follow inlet
flood tidal prism at 475 million cubic feet, with approximately 77.6 million cubic feet tidal prism assigned
to the Eastern Channel.
If the Eastern Channel is considered as a tidal inlet, the equilibrium cross - sectional channel area (Ac) can
be calculated for the reported tidal prism (P) using empirical relationships. The empirical relationship
determined by Jarrett (1976) for Atlantic Coast inlets is:
A, _ (7.75 x 10 -6) P""
For the Eastern Channel's reported tidal prism of 77.6 million cubic feet, the corresponding Ac = 1,492
square feet. Using Obrien's (1966) empirical calculations for the all inlets (including those with jetties),
the corresponding Ac = 2,000 square feet.
Currently near the west end of the Eastern Channel adjacent to Lockwoods Folly Inlet, the channel has
shoaled in with existing cross - sectional areas of 250 — 400 square feet. The proposed cross - sectional
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area to be provided is 2150 square feet. Along the reach of the main channel south of Sheeps Island,
the average cross - sectional area is currently 850 square feet with a proposed cross - sectional area of
approximately 1750 square feet.
Summary and Recommendations
Based on the sediment compatibility and analysis and consideration of channel stability, it is
recommended that the Town proceed with design and permitting following the proposed alignment
identified for Option 2. This option should provide improved channel stability as compared to Option 3
while providing more consistent beach compatible material than Option 1. Option 2 would be located in
the middle channel shown below in the existing bathymetry (Figure 4) as well as in Figure 3 (please note
the background aerial is not recent).
Legend
Elevation (NAVD88) .
-10.99 - -10.00
• -19.35 - -19.00 e
-9 99 - -9.00
• -18 99 - - 18.00 -
-8.99 - -8.00
• -17.99 - -17.00
-7.99 - -7.00
• -16.99 - -16.00
-6.99 - -6.00
• -15 99 - -15.00
-5.99 - -5.00
-14.99 - -14.00
-4.99 - -4.00
-13.99 - -1100
-3.99 - -100
-12.99 - -12.00
-2.99 - -2.00
• - 11.99- -11.00
0 250 500 1,000
1,500 2,000
Feet
� iwp
r;
-1.99 - -1.00
-0.99 - 0.00
0.01 -1.00
1.01 - 2.00
2.01 -3,00
3.01 -4.00
4.01 - 5.00
• 5.01 -6.00
• 6.01 -7.00
NN/y��yp
W FY4 b
S
Figure 4: Existing Bothymetry
`f
1
s,
References
Coastal Science & Engineering, 2009. Preliminary Design Report - Phase 1. Lower Lockwoods Folly River
Aquatic Habitat Restoration Project.
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