01 - Avon AppC)LargeSedimentSamplingReport

APPENDIX C
LARGE SEDIMENT SAMPLING
Prepared on Behalf of:
Dare County Board of Commissioners
North Carolina
In support of NEPA Documents Prepared for
Avon Village Beach Nourishment
Dare County, North Carolina
Prepared by:
PO Box 8056, Columbia, SC 29202–8056
[2525–TASK 4–MAY 2021]
LARGE SEDIMENT SAMPLING
DARE COUNTY, NORTH CAROLINA
MAY 2021
Prepared for:
North Carolina Department of Environmental Quality
Division of Coastal Management
Submitted by:
Dare County, North Carolina
[CSE2541]
MAY 2021
This report was prepared by the County of Dare under grant award
#NA18NOS4190071/#NA19NOS4190082 to the Department of Environmental Quality,
Division of Coastal Management from the Office for Coastal Managem ent, National
Oceanic and Atmospheric Administration. The statements, findings, conclusions, and
recommendations are those of the author(s) and do not necessarily reflect the views of
DEQ, OCM or NOAA.

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LARGE SEDIMENT SAMPLING
DARE COUNTY, NORTH CAROLINA
MAY 2021

Prepared by:

PO Box 8056, Columbia, SC 29202 –8056

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TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................................ i
1.0 INTRODUCTION ......................................................................................................................... 1
2.0 METHODOLOGY ......................................................................................................................... 5
3.0 RESULTS ................................................................................................................................. 11

APPENDIX A ) Clast Photographs

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1.0 INTRODUCTION
T he North Carolina Coastal Resources Commission (CRC) requires large sediment surveys prior to any
beach fill project, as part of several measures designed to ensure sand used for beach nourishment
closely matches the sand on the existing beach (CRC Rules 15A NCAC 07H.0312 Technical Standards for
Beach Fill Projects – referred to as CRC Rules herein). Large sediments are defined as sediment clasts
equal to or greater than one inch in diameter and shell material equal to or greater than three inches
in diameter.
This report presents the survey results completed along the beaches at Avon and Buxto n, Dare County,
North Carolina . The fieldwork was performed in March 2021 in preparation for upcoming
renourishment projects scheduled to take place at Avon and Buxton in 2022. Photo processing, data
analysis, and report writing were conducted from mid -April through early May 2021 under Grant
Contract No. CW20490 between the North Carolina Department of Environmental Quality and the
County of Dare.
The Buxton beach nourishment project encompass es 2.9 miles of oceanfront along the Village of
Buxton and the Cape Hatteras National Seashore (CHNS). The project is expected to place ~1.2 million
cubic yards (cy) of beach -compatible sediment dredged from a borrow area approximately two to three
miles offshore (Fig 1.1).
The Avon beach restoration study area encompass es 4.4 miles of oceanfront along the Village of Avon
and CHNS . The nourishment is expected to consist of ~1 million cy of beach -compatible sediment
dredged from a borrow area approximately tw o to three miles offshore placed along 2.5 miles of the
4.4 -mile oceanfront (Reaches 3 and 4 – Fig 1.2). Dare County may expand the nourishment area in the
future based on the beach condition and available funds . Therefore, large sedime nt samples were
collected along Reaches 1 through 5 to establish a baseline for the entire Avon study area.

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FIGURE 1.1. Map showing the 2022 nourishment project along the oceanfront in the vicinity of Buxton, Dare County, NC.

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FIGURE 1.2. Map showing the 2022 nourishment project along the oceanfront in the Village of Avon, Dare County, NC .

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2.0 METHODOLOGY
According to CRC Rules, t he survey was completed through visual observation of a 10,000 square foot
(ft2 ) area of the beach surface along at least five transects spaced no further than 5,000 feet (ft) apart
within the project areas at Avon and Buxton. For the large sediment survey, there were five transects
at Avon and seven located along Buxton. ‘Large sediments’ are defined as sediment equal or greater
than one inch in diameter, and shell material equal or greater than three inches in diameter.
The total length of the two projects is 7.3 miles. Samples were collected along twelve transects spaced
no greater than 5,000 ft apart (Fig 2.1 a-b ). Transect spacing varied from 1,000 and 3,000 ft and averaged
2,400 ft. Sampling locations were documented using real -time kinematic global positioning system
(RTK -GPS) hardware (Tr imble© Model R10 GNSS), and individual sediments were recorded using a
digital camera and ruler.
Photographs of the samples were examined , and the sediments were classified into three groups by a
licensed professional geologist. These groups are ‘shell,’ ‘sediment,’ and ‘anthropogenic .’ Basic
diagnostic characteristics of shell material include a smooth shiny surface, sharp angular edges (in the
case of shell fragments), scars from tube worms, radial ribs and/or growth rings (more useful for
bivalves), and an apex or siphonal notch (more useful for univalves – Figs 2.2 and 2.3 ).
Samples classified as ‘sediment’ were differentiated based on the common characteristics of marl and
beach rock common along many southeastern beaches. These types of sediments co mmonly exhibit
either more shell material or a more consistent grain size than anthropogenic materials like asphalt or
paving cement (Fig 2.4). Along the Outer Banks, anthropogenic material is often found on beaches
where chronic erosion has resulted in st ructural foundations or roads being undermined and eroded
by surf. These clasts are distinguished from natural beach rock because they often exhibit different
density/weight, surface roughness, and chemical makeup.

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FIGURE 2.1a . Sampling locations and survey stations along the Avon Beach restoration project area.

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FIGURE 2.1b. Sampling locations and survey stations along the Buxton Beach renourishment project area.

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FIGURE 2.2. Typical features of large sediment made of shell
material include a smooth shiny surfac e (upper left),
concentric growth rings or radial ribs (bottom right), or an
apex or siphonal notch common in univalves (top right). These
features are evident in weathe red as well as fresh samples,
making them useful diagnostic identifiers.
FIGURE 2.3. Even in heavily -weathered samples like the oyster shell shown above, tube worm
casts and scars remain a diagnostic feature of shell material over sediment or anthropogenic
clasts.

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FIGURE 2.4. Representative examples of natural (top) and anthropogenic (bottom) sediment samples . In
the natural sedimentary (top) sample, fine grains dominate with some larger shell fragments indicating
this is a likely a remnant of local beach rock. In the anthropogenic (bottom) sample, large gravel -sized
pieces of different metamorphic and igneous r ocks are interspersed within a fine -grained matrix – similar
to asphalt and certain types of paving cement.

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3.0 RESULTS
Large clast counts are listed by survey station in Table 3.1. Photographs of each individual clast are
provided in Appendix A. The baseline condition for the Avon project area before the 2022 nourishment
project shows an average of 5.2 large clasts per tra nsect with a total of 26 large clasts. The baseline
condition for the Buxton project area before the 2022 nourishment project shows an average of 22.0
large clasts per transect with a total of 154 large clasts .
Of the 2 6 clasts measured at Avon, 2 5 were s hell material (average of 5.2 shell clasts per transect), and
one was a sediment clast. Along Buxton, there was slightly more variability with ~2 0 shell clasts and
~2 sediment clasts per transect. Three anthropogenic clasts were observed at Buxton, on Stations
1820+00, 1900+00, and 1920+00.

TABLE 3.1. Survey results, with large clasts separated into ‘shell ,’ ‘sediment ,’ and ‘anthropogenic’ categories .