South Carolina Coastal Erosion Study

Physical Oceanography and Modeling

Long Bay, South Carolina, is a heavily populated coastal region that supports a large tourism industry. Sand resources are important for both recreation and coastal habitat. Earlier geological framework studies have identified a large sand deposit oblique to the shoreline, oriented clockwise in the offshore direction. This sand feature is ~ 10 km long, 2 km wide, and in excess of 3 meters thick, possibly providing a source for beach nourishment material (Figure 7).

Objectives of this study are to describe the physical processes that control the transport of sediment in Long Bay, specifically off the coast of Myrtle Beach, South Carolina. Specifically we seek to

1. measure and model the oceanographic circulation in the region,
2. identify the processes that maintain the presence of the offshore sand feature,
3. quantify the control that the shoal exerts on the nearshore through changes in wave energy propagation, and
4. identify consequences of removal of the offshore sand feature.

Field measurements and numerical modeling techniques are utilized in this project (Figure 8).

Figure 8. Deployment of instrumented tripod off the R/V Dan Moore.Click on image to view larger version.

Oceanographic and sediment transport observational systems were deployed for a period of 6 months (October 2003 to April 2004) at eight sites to measure wind forcing, currents, stratification, and wave spectral characteristics. Bed-flow interactions were measured at two locations, with instrumented tripods equipped with pairs of ADVs for measuring turbulence, PC-ADPs for measuring vertical current profiles in the near bed, and OBS and ABS for measuring suspended sediment concentrations. Numerical modeling of the hydrodynamic and sediment transport utilize ROMS for 3-D coastal circulation, SWAN for wave propagation on the inner shelf, and SHORECIRC for circulation in the nearshore. A focused short-term surf zone experiment was also carried out to investigate nearshore circulation and sediment transport.

Results indicate that currents in the study area are strongly influenced by both tidal motion and wind driven setup / setdown. The presence of the offshore sand feature alters the residual flows in the region. Sediment transport is more significant during periods of sustained strong winds that generate local waves. Wind direction plays a key role in determining the direction and magnitude of sediment transport.

Figure 9. Field deployment personnel onboard the R/V Dan Moore, owned and operated by Cape Fear Community College in Wilmington, NC. From left: Steve Ruane (USGS), John Warner (USGS), Jonathan Borden (USGS), George Voulgaris (University of South Carolina [USC]), Ben Gutierrez (USC), Duncan Smith (USC), Marinna Martini (USGS), and Stephanie Obley (USC). Not shown are Dan Hanes (USGS), Paul Work (Georgia Tech [GT]), and Kevin Haas (GT). Click on image to view larger version.