BACK-BARRIER EROSION THREATENS ARCHEOLOGICAL SITES ON CUMBERLAND ISLAND NATIONAL SEASHORE, GEORGIA

In contrast to the common problem of erosion threatening expensive new beachfront structures, Cumberland Island National Seashore is experiencing significant back-barrier erosion that is threatening invaluable archeological remains. Due to the prime location and captivating landscape, Cumberland Island has been inhabited or occupied throughout 4,000 years of history by Native Americans, Spanish, British, early Americans and African Americans. The fact that a great deal of our country’s cultural record has been preserved by the relatively pristine nature of this island, lends unparalleled archeological significance to Cumberland. However, many of the historic features established throughout time were strategically located along the multifaceted back-barrier shoreline, which is now undergoing erosion.

Cumberland Island is the largest and southernmost barrier along Georgia’s mesotidal coast (mean tidal range ~2m). This 30 km-long barrier is backed by a well-developed marsh and tidal creek system, with three rivers flowing into the Intracoastal Waterway. Where the cutbanks of these rivers and tidal creeks are migrating into the barrier sands, prominent erosional scarps are present.

The majority of the barrier islands along the Georgia coast are experiencing back-barrier erosion and yet few investigations have been preformed to study this phenomenon. A joint project by the Geological Society of America and the National Park Service is looking into the contributing factors and erosion rates along the western shore of Cumberland Island. Preliminary shoreline change studies using air photo analysis, and limited geomorphic profile comparison, have generated approximate rates of erosion between 15-50 cm/y. To augment this remote sensing data and ground-truth these erosion rates, geomorphic profile stations have been established and a monitoring program implemented. However, in order to fully quantify the impact of various factors such as: sea-level rise, storms, tides, vessel wake, and devegetation by grazing, it is necessary to perform continued research over the next several years. The purpose of such a long-term study is twofold: 1) to better understand the dynamics of back-barrier erosion, and 2) determine the optimal management approach with respect to the high risk archeological sites.