ERDC/CHL CHETN-II-47
March 2004
South of the Dare County beach-fill area there are six other identified natural hot spots along the
Outer Banks that require coastal engineering to protect the single access road for the southern Outer
Banks. These hot spots extend south of Oregon Inlet to Ocracoke Island (Figure 11b). All six of
these hot spots may have a link to underlying geology, which focuses wave activity. These hot spots
areas have frequent overwash of the highway and road inundation during storms. At (1) Northern
Pea Island (National Wildlife Refuge) and (2) Old Sand Bag Area (also in the Refuge) sand is
placed on the beach just south of the inlet from channel maintenance dredging at Oregon Inlet and
the net southward drift carries sand to the hot spot areas. Dunes have been constructed to help
prevent overwash. At (3) Rodanthe S Curve, the highway has been relocated landward of the main
overwash area. This area of the barrier island extends seaward so shoreline orientation plays a part in
this hot spot. The updrift coast is oriented northwest-southeast and the downdrift coast is oriented
northeast-southwest. At (4) Buxton/Canadian Hole, the road has also been relocated landward. This
site has had several breaches during large storms with inlet formation. These breaches have been
closed mechanically with emergency dredging of sand from the bay to prevent new inlet formation.
At (5) Hatteras Village on the east/west oriented coast south of Cape Hatteras, the road has been
overwashed along a narrow portion of the island. Hurricane Isabel on 18 September 2003 cut a
breach in the island in this vicinity. Across Ocracoke Inlet, at (6) Ocracoke Island, overwash covers
the road during storms. A dune has been built to try to prevent this overwash. All of these hot spots
on the Outer Banks are suspected to be from wave focusing over nearshore shoals and were sites of
overwash and road inundation during Hurricane Isabel.
Myrtle Beach, SC. Myrtle Beach is located along the northern South Carolina coast and was filled
in 1987, 2 years before Hurricane Hugo made landfall in 1989. The project was constructed in three
phases that covered Phase I in North Myrtle Beach, Phase II in Myrtle Beach, and Phase III in
Surfside/Garden City (Figure 12). The nearshore area has a complex geology as evidenced by
sidescan surveys conducted by the U.S. Geological Survey (USGS). The nearshore contains rock
outcrops and seaward movement of the fill material was inferred by successive sidescan surveys.
Data and interpretation was provided by Paul T. Gayes, Center for Marine and Wetland Studies,
Coastal Carolina University. The local and regional geologic framework plays an important role in
fill movement and hot spot formation in this project. The fill was placed in a sediment starved
system and the fill moved offshore. The loss of sand from the project could not be explained by end
losses alone. Localized sand loss to the offshore occurs at low rates so hot spot designation is not
entirely accurate. Loss from all areas of fill resulted in poor performance of the fill. Survey evidence
shows that the fill sand occupied the nearshore for some 9 months then was eroded and rock was
exposed again in the nearshore within 15 months after placement (Figure 13).
Folly Beach, SC. Folly Beach is located south of Charleston, SC. A beach fill was placed in 1992
along the entire length of the barrier island. Three hot spots have developed along the project
(Figure 14). The first hot spot is located at the northern end of the project where there is a change in
shoreline orientation just south (downdrift) of the ebb shoal attachment point of Lighthouse Inlet.
This hot spot area is known locally as the "washout." Nearshore wave transformation and shoreline
change modeling indicated a high rate of erosion during the design formulation phase of the project
(Ebersole and Neilans 1997). Change in shoreline orientation and possible focusing of wave energy
by irregular offshore bathymetry are potential contributors to this hot spot. No design modifications
were taken because of an existing rock revetment that supplied storm damage protection to the
houses in the area.
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