REGIONALLY LINKING THE ACTIVE BEACH ACROSS THE SHOREFACE AND INNER SHELF: THE SC COASTAL EROSION PROJECT

A comprehensive geophysical survey (side scan sonar, bathymetry, sub bottom profiling) of the inner continental shelf has been completed by the USGS along 80 km of the northern South Carolina coast. These records, groundtruthed by vibracores, surficial sediment samples and bottom video, are providing a comprehensive regional framework for the investigation of many basic and applied questions in the coastal zone. This integrating regional framework approach has generated great interest from and interaction with numerous federal, state and local organizations addressing a wide range of concerns (i.e. sand resources, critical benthic habitats, coastal management etc.).

In addition to the broad alongshore scope of geophysical mapping, the SC program is being extended across the shoreface to the active beach system. This allows direct imaging of the critical area where linkage of short-term active beach changes ("engineering-event" time scales) and longer-term coastwise transgression/migration ("geologic" time scales) is needed to improve prediction of future coastal behavior. The approach has greatly aided the interpretation of substantial alongshore variations in beach fill stability observed at a recent large (>$50M) beach nourishment project in the area. Areas of low stability of the recently constructed beaches coincide with zones of localized offshore movement of sand and extensive rocky outcrops interrupting nearshore bathymetry, sediment dispersal pathways and presumably processes.

Long-term regional need for sand will require either identification of more numerous but small inshore sources or larger but more distant offshore reserves than presently considered. The recent regional framework mapping identified a significant sand deposit removed from the depositional settings typically targeted by past, more limited project-specific studies. In such a sand-starved region, where the state is committed to beach nourishment options and is already drawing sand from beyond the 3-mile limit, the regionally comprehensive framework approach is necessary to efficient manage the available coastal sand and biological resources, reliably project the long term cost of use of these resources and provide important constraints for planning and design of future projects.