USING GEOSPATIAL TOOLS TO QUANTIFY THE THREAT TO ARCHAEOLOGICAL, HISTORIC AND CULTURAL RESOURCES FROM SHORELINE CHANGE: THE GEORGIA COAST EXAMPLE

Shoreline erosion along open coastlines and bluffs of tidal streams impacts important archaeological sites by exposing, removing and destroying burials, structures, and artifacts. In this study we identified sites on barrier islands and back-barrier islands (“marsh hammocks”) in coastal Georgia that are threatened and/or are being damaged by coastal erosion, evaluated their site condition and prioritized them for documentation based on the order of site loss.

All archaeological sites within a 30 m radius of a waterway or marsh environment were selected from the Georgia Archaeological Site file (GASF) database, as these were the sites that might be destroyed within the next 50 years, based on average back-barrier erosion rates. This list was evaluated by the Georgia Department of Natural Resources – Historic Resources Division (DNR-HPD) to identify sites that were potentially listable on the Federal Register of Historic Places. For each of the sites, projects were generated in ARCGIS that included a current, GPS-surveyed shoreline and shorelines derived from historic maps and aerial imagery. AMBUR (Analysis of Moving Boundaries Using “R”; Jackson et al., 2012) was then used to calculate shoreline change rates. Using these site-specific rates, we created a prioritized list of archaeological sites based on the time until each site was destroyed by erosion and the information contained within it was lost.

For the 21 sites on barrier islands, 11 shorelines (52%) were eroding, 8 were stable, and 2 were accreting. For the 36 sites on back-barrier islands, 29 shorelines (81%) were eroding, and 7 were stable. Higher shoreline change rates were observed at barrier island sites (up to -1.7 m/y erosion) when compared to back-barrier island sites (rates up to -0.7 m/y erosion), although the dynamic back-barrier environment exhibited a higher percentage of erosional sites. Consequently, archaeological sites on barrier islands typically experience a higher annual percentage loss of site information than do sites on back-barrier islands. The projected lifetime of sites varies greatly, ranging from less than a year (and some sites had completely eroded away at the time of our survey) to several hundred years depending on shoreline change rate, site location and site size.