AN EVALUATION OF SHORELINE DYNAMICS AT ST. CATHERINES ISLAND, GEORGIA (1859-2009) UTILIZING THE DIGITAL SHORELINE ANALYSIS SYSTEM (USGS)

St. Catherines Island is one of twelve barrier islands fringing the Georgia Coast (Foyle et al., 2004), located approximately 32 kilometers (20 miles) south of Savannah, Georgia. St. Catherines Island is bordered by the Atlantic Ocean to the east, tidal marshes to the west, Sapelo Sound to the south and St. Catherines Sound to the north. These sounds are the lower reaches of salt water estuaries or marine embayments that are devoid of actual river input or discharge. As a result, St. Catherines Island is dependent upon the net longshore transport of sediment from north to south along the Georgia Coast. An extrapolated sea level rise rate of 2.7 mm/yr for the area near St. Catherines Island is yielded from published values along the southeastern coast. The combination of factors, including the interruption of the flow of sediment by impounding rivers to the north and dredging of navigable channels, and rising sea level have accumulated to make St. Catherines one of Georgia's most erosional barrier islands (Griffin and Henry, 1984). Traditional methods of evaluating shoreline dynamics were based on manual cartographic and calculation methods and indicated a net shoreline retreat or erosion rate of 4.3 meters/year (m/yr) along the north-central portion of the island, 2.5 m/yr along the south central portion of the island, and a significant erosion rate of 8.2 m/yr along the Sapelo Sound margin. More modern methods have employed the use of Geographic Information System (GIS) software to aid in determining shoreline dynamics (Langley, et al., 2003). The United States Geological Survey (USGS) Digital Shoreline Analysis System (DSAS) Version 4.1, that operates within the Environmental Systems Research Institute (ESRI) ArcGIS software as an extension is a freely available software application that computes rate-of-change statistics for a time series of shoreline vector data. The current study has utilized modern remote sensing data, digital imagery and DSAS Version 4.1 to generate statistics of shoreline change and compared these results against the previous studies of Griffin and Henry (1984) and others. In addition, the rates of erosion and accretion have been evaluated in a qualitative manner with respect to the island’s landforms and geomorphology.