08 - Avon - AppA-Attachment 4

Coastal Science & Engineering Geotechnical Data Analysis
[2525–Task 4–Appendix A] Avon, Dare County, North Carolina

APPENDIX A

ATTACHMENT 4

NC Technical Standards for Beach Fill
(15A NCAC 07H.0312)

Effective 1 April 2021

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NARRATIVE – ATTACHMENT 1
15A NCAC 07H .0312 TECHNICAL STANDARDS FOR BEACH FILL PROJECTS (effective April 2021)
Placement of sediment along the oceanfront shoreline is referred to in this Rule as "beach fill." Sediment
used solely to establish or strengthen dunes shall conform to the standards contained in 15A NCAC 07H
.0308(b). Sediment used to re-establish state-maintained transportation corridors across a barrier island
breach in a disaster area as declared by the Governor is not considered a beach fill project under this Rule.
Beach fill projects including beach nourishment, dredged material disposal, habitat restoration, storm
protection, and erosion control may be permitted under the following conditions:
(1) The applicant shall characterize the recipient beach according to the following methodology. Initial
characterizations of the recipient beach shall serve as the baseline for subsequent beach fill
projects:
(a) Characterization of the recipient beach is not required for the placement of sediment directly
from and completely confined to a maintained navigation channel or associated sediment
basins within the active nearshore, beach or inlet shoal system. For purposes of this Rule,
“cape shoal systems” include Frying Pan Shoals at Cape Fear, Lookout Shoals at Cape Lookout,
and Diamond Shoals at Cape Hatteras;
N/A
(b) Sediment sampling and analysis shall be used to capture the spatial variability of the sediment
characteristics including grain size, sorting and mineralogy within the natural system;
Sediment samples were collected at five (5) stations along the beach and fourteen (14) cross-shore
locations between the foredune and 24 ft depth contour within the proposed project area.
Samples were also collected at various locations and multiple depths within the proposed borrow
area to capture the three-dimensional spatial variability of the sediment characteristics.
(c) Shore-perpendicular transects shall be established for topographic and bathymetric surveying
of the recipient beach. Topographic and bathymetric surveying shall occur along a minimum
of five shore-perpendicular transects evenly spaced throughout the entire project area with
spacing not to exceed 5,000 feet (1,524 meters) in the shore-parallel direction. Each transect
shall extend from the frontal dune crest seaward to a depth of 20 feet (6.1 meters) or to the
shore-perpendicular distance 2,400 feet (732 meters) seaward of mean low water, whichever
is in a more landward position. Elevation data for all transects shall be compliant with
Standards of Practice for Land Surveying in North Carolina (21 NCAC 56.1600);
Shore-perpendicular, topographic and bathymetric surveying of the recipient beach was
conducted in July 2020 at Avon. The surveying extends from the foredune seaward to a depth of
over 40 feet. Forty-seven (47) transects were surveyed along the ~2.5-mile project area and the
adjacent areas, and the spacing between each transect was 500 ft. Elevation data for all transects
are referenced to the North American Vertical Datum of 1988 (NAVD 88) and the North American
Datum of 1983 (NAD 83). Details of the survey and its results are described in the Environmental
Assessment (EA) – Appendix D - Littoral Processes.
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(d) Along each transect, at least one sample shall be taken from each of the following
morphodynamic zones where present: frontal dune, frontal dune toe, mid berm, mean high
water (MHW), mid tide (MT), mean low water (MLW), trough, bar crest and at even depth
increments from 6 feet (1.8 meters) to 20 feet (6.1 meters) or to a shore-perpendicular
distance 2,400 feet (732 meters) seaward of mean low water, whichever is in a more landward
position. The total number of samples taken landward of MLW shall equal the total number
of samples taken seaward of MLW;
Sediment samples were collected along five beach transects in March 2021 (see the Geotechnical
Report). Fourteen (14) samples were taken along each beach transect at the following cross-shore
locations (see Figures 10 and 11 in the Narrative or Figure 2.1 in the Geotechnical Report):
• dune face
• toe of the dune
• berm
• berm crest
• MHW
• MTL
• MLW
• Trough
• inshore bar
• -8 ft NAVD
• -12 ft NAVD
• -16 ft NAVD
• -20 ft NAVD
• -24 ft NAVD
There are 7 samples taken landward of MLW (including MLW) and 7 samples taken seaward of
MLW (not including MLW).
(e) For the purpose of this Rule, "sediment grain size categories" are defined as "fine" (less than
0.0625 millimeters), "sand" (greater than or equal to 0.0625 millimeters and less than 2
millimeters), "granular" (greater than or equal to 2 millimeters and less than 4.76 millimeters)
and "gravel" (greater than or equal to 4.76 millimeters and less than 76 millimeters). Each
sediment sample shall report percentage by weight of each of these four grain size categories;
Sediment samples were inspected for mud then washed, dried, weighed in splits for analysis of
grain size, gravel, and shell content (see Sections 3 and 4 of the Geotechnical Report). Grain size
distribution of each sample is shown in Attachment 1 of the Geotechnical Report. Descriptive
statistics (mean, standard deviation, skewness, and kurtosis), along with USCS and Wentworth
descriptions, and shell and gravel contents, are compiled in Tables 3.1a and 3.1b. Tables 3.2 and
3.3 contain mean grain sizes, standard deviations, and shell and gravel contents averaged by
station as well as cross shore position. Overall, materials on the native beach and the borrow
areas are both defined as “sand” based on the Rule with fine-grained sediment contents for the
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recipient beach are less than 1%, and the average granular and gravel content (grain size greater
than or equal to 2 millimeters) is 1.8% (see Tables 3.3 and Figure 3.1 of the Geotechnical Report).
Detailed results for the proposed borrow areas are in included in Section 4 of the Geotechnical
Report.
(f) A composite of the simple arithmetic mean for each of the four grain size categories defined
in Sub-Item (1)(e) of this Rule shall be calculated for each transect. A grand mean shall be
established for each of the four grain size categories by summing the mean for each transect
and dividing by the total number of transects. The value that characterizes grain size values
for the recipient beach is the grand mean of percentage by weight for each grain size category
defined in Sub-Item (1)(e) of this Rule;
Mean (and a grand mean for composite samples) grain size for individual samples and composite
samples are summarized in Tables 3.1 to 3.3 and plotted in Figures 3.1 to 3.4 of the Geotechnical
Report. The grand mean grain diameter of all beach samples collected in March 2021 is 0.289
mm. The mean content by weight of fine-grained and granule-size sediment for the recipient beach
is less than 1%, and gravel contents (grain size between 4 and 76 millimeters) is 1.8% (see Tables
3.1 to 3.3).
(g) Percentage by weight calcium carbonate shall be calculated from a composite of all sediment
samples. The value that characterizes the carbonate content of the recipient beach is a grand
mean calculated by summing the average percentage by weight calcium carbonate for each
transect and dividing by the total number of transects;
Calcium carbonate (CaCO3) content (ie – “shell” content) was determined by acid-burning using
dilute hydrochloric acid. Percentage by weight calcium carbonate was calculated for each sample
as well as for a composite of all samples along each transect. The results are listed in Tables 3.1
to 3. of the Geotechnical Report, and plotted in Figure 3.4 of the same report. The arithmetic
average shell content for all samples (n=70) was 4.0% in March 2021 (see Table 3.3).
(h) The number of sediments greater than or equal to one inch (25.4 millimeters) in diameter,
and shell material greater than or equal to three inches (76 millimeters) in diameter shall be
calculated for an area of 10,000 square feet centered on each transect, and between mean
tide level (MTL) and the frontal dune toe within the beach fill project boundaries. A simple
arithmetic mean shall be calculated for both sediments and shell by summing the totals for
each across all transects and dividing by the total number of transects, and these values shall
be considered representative of the entire project area, and referred to as the “background”
values for large sediment and large shell material;
Some material greater than or equal to three inches (76 millimeters) in diameter was observed
along the beach in March 2021. A large-clast survey was conducted in five ~10,000 square-foot
areas within the Avon project area in March 2021. Survey results show that there was an average
of five sediments larger than 3” in diameter per transect.
(i) Beaches that received sediment prior to the effective date of this Rule shall be characterized
in a way that is consistent with Sub-Items (1)(a) through (1)(h) of this Rule and may use data
collected from the recipient beach prior to the addition of beach fill where data are available,
and in coordination with the Division of Coastal Management; and
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N/A
(j) All data used to characterize the recipient beach shall be provided in digital and hardcopy
format to the Division of Coastal Management upon request.
All data were described, analyzed, compiled, and plotted in Appendix A – Geotechnical Data.
Digital and hardcopy of the report has been submitted to the Division of Coastal Management.
(2) Characterization of borrow areas is not required if completely confined to a cape shoal system. For
the purposes of this Rule, “cape shoal systems” include the Frying Pan Shoals at Cape Fear,
Lookout Shoals at Cape Lookout, and Diamond Shoals at Cape Hatteras. The applicant shall
characterize the sediment to be placed on the recipient beach according to the following
methodology:
(a) The characterization of borrow areas including submarine sites, upland sites, and dredged
material disposal areas shall be designed to capture the spatial variability of the sediment
characteristics including grain size, sorting and mineralogy within the natural system or
dredged material disposal area;
A variety of potential borrow areas have been evaluated. Details are described in Section 4 of the
Geotechnical Report.
(b) The characterization of borrow sites may include historical sediment characterization data
where available and collected using methods consistent with Sub-Items (2)(c) through (2)(g)
of this Rule, and in coordination with the Division of Coastal Management;
N/A
(c) Seafloor surveys shall measure elevation and capture acoustic imagery of the seafloor.
Measurement of seafloor elevation shall cover 100 percent, or the maximum extent
practicable, of each submarine borrow site and use survey-grade swath sonar (e.g. multibeam
or similar technologies). Seafloor imaging without an elevation component (e.g. sidescan
sonar or similar technologies) shall also cover 100 percent, or the maximum extent
practicable, of each site. Because shallow submarine areas can provide technical challenges
and physical limitations for acoustic measurements, seafloor imaging without an elevation
component may not be required for water depths less than 10 feet (3 meters). Alternative
elevation surveying methods for water depths less than 10 feet (3 meters) may be evaluated
on a case-by-case basis by the Division of Coastal Management. Elevation data shall be tide-
and motion-corrected and compliant with Standards of Practice for Land Surveying in North
Carolina (21 NCAC 56.1600). Seafloor imaging data without an elevation component shall also
be compliant with Standards of Practice for Land Surveying in North Carolina (21 NCAC
56.1600) of the N.C. General Statutes. For offshore dredged material disposal sites, only one
set of imagery without elevation is required. Sonar imaging of the seafloor without elevation
is not required for borrow sites completely confined to maintained navigation channels,
sediment deposition basins within the active nearshore, beach or inlet shoal system;
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A detailed bathymetric survey with 1000-ft spacing for track lines of proposed borrow area was
completed by CSE in July 2020. A submerged cultural resource remote-sensing survey of the
proposed borrow area is described in Appendix G – Cultural Resources Survey.
The proposed borrow areas are situated 2 to 3 miles off Avon Pier. The depths of the areas are
from 35 ft to 60 ft with an average of ~45 ft below NAVD. A marine cesium magnetometer and
digital sidescan sonar along with other supporting equipment will be employed to collect
bathymetric, magnetic and acoustic data. Details of the study will be included in EA Appendix G –
Cultural Resources Study.
(d) Geophysical imaging of the seafloor subsurface shall be used to characterize each borrow site.
Because shallow submarine areas can pose technical challenges and physical limitations for
geophysical techniques, subsurface data may not be required in water depths less than 10
feet (3 meters), and the Division of Coastal Management shall evaluate these areas on a case-
by-case basis. Subsurface geophysical imaging shall not be required for borrow sites
completely confined to maintained navigation channels, and for sediment deposition basins
within the active nearshore, beach or inlet shoal system, or upland sites. All final subsurface
geophysical data shall use accurate sediment velocity models for time-depth conversions and
be compliant with Standards of Practice for Land Surveying in North Carolina (21 NCAC
56.1600;
To ensure sufficient data would be available to locate any potentially significant magnetic
anomalies and sonar targets in the proposed borrow area, remotely sensed data are co llected
along parallel lanes spaced on 50-foot intervals. A submerged cultural resource remote sensing
survey of the proposed borrow area is described in Appendix G – Cultural Resources Survey.
(e) With the exception of upland borrow sites, sediment sampling of all borrow sites shall use a
vertical sampling device no less than 3 inches (76 millimeters) in diameter. Characterization
of each borrow site shall use no fewer than five evenly spaced cores or one core per 23 acres
(grid spacing of 1,000 feet or 305 meters), whichever is greater. Characterization of borrow
sites completely confined to maintained navigation channels or sediment deposition basins
within the active nearshore, beach or inlet shoal system shall use no fewer than five evenly
spaced vertical samples per channel or sediment basin, or sample spacing of no more than
5,000 linear feet (1,524 meters), whichever is greater. Two sets of sampling data (with at
least one dredging event in between) from maintained navigation channels or sediment
deposition basins within the active nearshore, beach or inlet shoal system, or offshore
dredged material disposal site (ODMDS) may be used to characterize material for subsequent
nourishment events from those areas if the sampling results are found to be compatible with
Sub-Item (3)(a) of this Rule. Vertical sampling shall penetrate to a depth equal to or greater
than permitted dredge or excavation depth or expected dredge or excavation depths for
pending permit applications. Because shallow submarine areas completely confined to a
maintained navigation channel or associated sediment basins within the active nearshore,
beach or inlet shoal systems can pose technical challenges and physical limitations for vertical
sampling techniques, geophysical data of and below the seafloor may not be required in water
depths less than 10 feet (3 meters), and shall be evaluated by the Division of Coastal
Management on a case-by-case basis;
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Cores at the proposed offshore borrow areas were obtained via vibracore (Section 2.2 of Appendix
A – Geotechnical Data). Lengths of all cores across the borrow area s were 10.0 ft (see Section 4
and Table 4.1 of the Geotechnical Report). There are 7 cores in the ~150-acre proposal Borrow
Area 1 (10 ft cut), yielding a core density of 1 core per ~20 acres, and 5 cores in the ~100-acre
proposed Borrow Area 2 (6 ft cut), yielding a core density of 1 core per ~20 acres (see Sheets 11
and 12 of Drawings). The proposed excavation depths are 10 feet below the existing grade within
Borro w Area 1 and 6 feet below the existing grade within Borrow Area 2. Existing core logs are
included in Attachment 2 of the Geotechnical Report.
(f) Grain size distributions shall be reported for all sub-samples taken within each vertical sample
for each of the four grain size categories defined in Sub-Item (1)(e) of this Rule. Weighted
averages for each core shall be calculated based on the total number of samples and the
thickness of each sampled interval. A simple arithmetic mean of the weighted averages for
each grain size category shall be calculated to represent the average grain size values for each
borrow site. Vertical samples shall be geo-referenced and digitally imaged using scaled, color-
calibrated photography;
All sediment samples within each vertical sample were inspected for mud then washed, dried,
weighed in splits for analysis of grain size, gravel, and shell content (see the methodology in
Section 2 of the Geotechnical Report). Grain size distribution of each sample is shown in
Attachment 3A of the Geotechnical Report. Descriptive statistics for samples in the borrow areas
(mean, standard deviation, skewness, and kurtosis), along with USCS and Wentworth descriptions,
and shell and gravel contents, are compiled in Tables 4.1a and 4.1b. Tables 4.2, 4.3, and 4.4
contain the same information for individual cores composited to a specified depth (eg 6 ft, 8 ft, 10
ft).
When composited to the 10-ft dredge depth, the mean grain size within Borrow Area 1 is 0.308
mm. The fine-grained and gravel -size sediment contents for Borrow Area 1 are less than 1%,
granule-size contents average 2.8%, and shell content is generally less than 15% with an average
of 16.4%. In Borrow Area 2, the 6-foot composite grain size is 0.331 mm. Fine-grained sediment
contents are less than 3%, granular content is 5.1%, gravel content is 0.7%, and shell content is
generally less than 15% with an average of 16.8% (see Tables 4.1 and 4.4 of the Geotechnical
Report).
(g) Percentage by weight of calcium carbonate shall be calculated from a composite sample of
each core. A weighted average of calcium carbonate percentage by weight shall be calculated
for each borrow site based on the composite sample thickness of each core. Carbonate
analysis is not required for sediment confined to maintained navigation channels or
associated sediment deposition basins within the active nearshore, beach or inlet shoal
system; and
Calcium carbonate (CaCO3) content (ie – “shell” content) was determined by acid-burning using
dilute hydrochloric acid (see Table 4.1 of the Geotechnical Report). Percentage by weight calcium
carbonate was also calculated for a composite of each core at different thickness intervals. The
results are listed in Tables 4.2, 4.3, 4.4, and 5.1 of the Geotechnical Report. Table 4.4 shows the
arithmetic average for all cores composited to 10 ft across Borrow Area 1 is 16.4% and composited
to 6 ft across Borrow Area 2 is 16.8%. Both values are ~ 12% greater than the recipient beach.
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(h) All data used to characterize the borrow site shall be provided in digital and hardcopy format
to the Division of Coastal Management upon request.
All data were described, analyzed, compiled, and plotted in the Geotechnical Report. Digital and
hardcopy of the report has been submitted to the Division of Coastal Management.
(3) Compliance with these sediment standards shall be certified by an individual licensed pursuant to
Chapter 89C or 89E of the N.C. General Statutes. Sediment compatibility is determined using the
following criteria:
(a) Sediment completely confined to the permitted dredge depth of a maintained
navigation channel or associated sediment deposition basins within the active
nearshore, beach or inlet shoal system is considered compatible if the average
percentage by weight of fine-grained (less than 0.0625 millimeters) sediment is less
than 10 percent;
(b) The average percentage by weight of fine-grained sediment (less than 0.0625
millimeters) in each borrow site shall not exceed the average percentage by weight
of fine-grained sediment of the recipient beach characterization plus five percent
(c) The average percentage by weight of granular sediment (greater than or equal to 2
millimeters and less than 4.76 millimeters) in a borrow site shall not exceed the
average percentage by weight or coarse-sand sediment of the recipient beach
characterization plus 10 percent
(d) The average percentage by weight of gravel (greater than or equal to 4.76 millimeters
and less than 76 millimeters) in a borrow site shall not exceed the average percentage
by weight of gravel-sized sediment for the recipient beach characterization plus five
percent;
(e) The average percentage by weight of calcium carbonate in a borrow site shall not
exceed the average percentage by weight of calcium carbonate of the recipient beach
characterization plus 15 percent; and
(f) Techniques that take incompatible sediment within a borrow site or combination of
sites and make it compatible with that of the recipient beach characterization shall
be evaluated on a case-by-case basis by the Division of Coastal Management.
(4) Excavation and placement of sediment shall conform to the following criteria:
(a) In order to protect threatened and endangered species, and to minimize impacts to
fish, shellfish and wildlife resources, no excavation or placement of sediment shall
occur within the project area during any seasonal environmental moratoria
designated by the Division of Coastal Management in consultation with other State
and Federal Agencies, unless specifically approved by the Division of Coastal
Management in consultation with other State and Federal agencies. The time
limitations shall be established during the permitting process and shall be made
known prior to permit issuance; and;
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(b) The total sediments with a diameter greater than or equal to one inch (25.4
millimeters), and shell material with a diameter greater than or equal to three inches
(76 millimeters) is considered incompatible if it has been placed on the beach during
the beach fill project, is observed between MTL and the frontal dune toe, and is in
excess of twice the background value of material of the same size along any 10,000
square feet section of beach within the beach fill project boundaries. In the event that
more than twice the background value of incompatible material is placed on the
beach, it shall be the permittee’s responsibility to remove the incompatible material
in coordination with the Division of Coastal Management and other State and Federal
resource agencies.