EVOLUTION OF A NON-UNIFORM SHOREFACE GEOMETRY: CASE STUDIES FROM SOUTH CAROLINA, USA

Traditionally, shoreline change has been defined in subaerial features or datums such as the wet-dry line or the MHW contour. The Beach Erosion Research and Monitoring (BERM) program funded by the state of South Carolina has provided 13 years of shore-perpendicular beach profiles from South Carolina's beaches, extending from landward of the primary dune to below the predicted depth of closure. Most efforts for predicting the long term trend of shoreline change are based on some variation of the Bruun Rule, which assumes that profile geometry remains uniform through rising sea level. BERM's extensive data set offers evidence that not all portions of the profiles are migrating uniformly. At one study area, BERM data illustrate accretion occurring in the dunes and upper shoreface while lower portions of the profile continue to erode. A second study area, influenced by a seawall, is classified by the State as having zero net erosion due to the artificial stabilization of the upper shoreface. At this same location, data from BERM's extended time series offers evidence that the lower shoreface is continuing its landward retreat. The resulting change in shoreface geometry may in turn affect nearshore hydrodynamics thus leading to modified rates of shoreline change. In practice, most coastal zone policy and engineering projects focus extensively on the behavior of the upper shoreface based upon short term coastal behavior. As the population of many coastal zone areas continues to expand, the demand for informed decision making regarding the coast will only grow in importance.