Integrating high-resolution mapping of the seafloor with sediment-transport measurements to understand coastal erosion in northern South Carolina
Abstract
Shoreline behavior along the coast of Long Bay, South Carolina is dictated by waves, tidal currents, and sediment supply that act within the overall constraints of the regional geologic setting. This study examined the influence of the geologic framework on coastal evolution through the interpretation of high-resolution geophysical data (swath bathymetry, sidescan-sonar imagery, seismic-reflection profiles), bottom samples and cores. Interpreted geophysical data were used to form conceptual models of sediment flux in the nearshore area, which are being tested by conducting site-specific sediment transport and oceanographic measurements and modeling. The inner shelf of Long Bay extends from the shoreface to about 10 km offshore (5-15 m water depth). It is underlain by coastal-plain strata of Cretaceous/Tertiary age that are incised by large fluvial channels formed during the Pliocene and Pleistocene. The indurated coastal-plain and channel-fill deposits are exposed as hardgrounds over large expanses of the inner shelf, and locally overlain by a discontinuous veneer of sandy Holocene sediment generally less than 1-m thick. A regional unconformity, thought to represent erosion during the most recent marine transgression, coincides with the seafloor in these areas of sparse sediment. Minor bathymetric highs occur where relatively thicker accumulations of Holocene sediment lie above the low- relief, transgressive unconformity. One of the thickest accumulations of Holocene sediment is contained within an anomalous, shore-oblique sand body that lies 3 km offshore of Myrtle Beach and is not associated with a modern tidal inlet. The lobate deposit is approximately 11-km long, 3-km wide, and up to 3-m thick. Cores show that the shoal is a marine deposit less than 5000 years old with a gravelly lag at the base representing the transgressive surface. It contains an estimated volume of 26 million m3 of sediment, largely consisting of fine to medium, well sorted quartz sand and is a potential source of material for planned beach nourishment projects in the Myrtle Beach area. Experiments are presently underway to determine the influence of modern hydrodynamic processes in maintaining and/or modifying the sand body. This study represents an interaction of geologists, geophysicists, modelers, and physical oceanographers that is necessary to increase our basic understanding of inner-shelf processes and coastal evolution/behavior. Such an interdisciplinary approach advances the development of a predictive capability (prediction of coastal change) that can be used by the coastal planning/engineering community.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMNS24A..01B
- Keywords:
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- 1835 Hydrogeophysics;
- 1861 Sedimentation (4863);
- 3006 Marine electromagnetics;
- 3020 Littoral processes;
- 4217 Coastal processes