ASSESSING TRENDS IN COASTAL VARIABILITY USING MODERN MAPPING TECHNIQUES

Accurate documentation of coastal change is an essential component of coastal research and management issues. Assessing trends in coastal behavior such as shoreline change, topographic and bathymetric relief, and beach volume has strong implications related to coastal planning, management and tourism. These trends can vary both spatially and temporally, making documentation difficult and often impractical. A 2.4 km section of Myrtle Beach, South Carolina serves as the study site since an extensive database of beach profiles, side scan imagery, bathymetry, and previous research exists. This integrated approach to coastal mapping incorporates nearshore video imaging and high-resolution real-time kinematic GPS (RTK-GPS) surveys in order to identify local trends in coastal variability. Nearshore video imaging of this site provides continuous observations of the beach and nearshore region, illustrating rapid changes and unique patterns in beach morphology and sandbar formation. Digital elevation models (DEM’s) created from RTK-GPS data provide a quantitative measure of longshore variability in shoreline position and beach geometry. From December 2002 to September 2003, seven RTK-GPS surveys were completed. Preliminary results show a distinct pattern in the longshore variability of shoreline and geometric change. A 640 m section in the southern portion of the study area has a shoreline change envelope of 12 m on average. This high change area transitions distinctly to a 500 m long area characterized by low change (average change of 3.5 m). A time series of DEM’s indicates a region of high geometric variability corresponding to the region of high shoreline change. Geo-rectified video imagery illustrates rapid formation of small beach cusps and a longer-term welding sandbar, which appears to correspond with the distinct trends in shoreline and morphologic change. Results show that the response to Hurricane Isabel, as represented by changes in slope, elevation, and volume, were spatially distinct between the ‘high-change’ and ‘low-change’ portions of the study area. Changes in beach geometry throughout the large coastal storm similarly fit observed trends in longshore variability. We suggest that this integrated approach to assessing coastal change is suitable for analyzing local trends in coastal behavior.