LANDFORM DYNAMICS ASSOCIATED WITH MISSION SANTA CATALINA DE GUALE: ST. CATHERINES ISLAND, GEORGIA

St. Catherines Island is a Georgia barrier island that hosts significant archaeological sites in close proximity to an extremely active shoreline. St. Catherines Island is bordered by the Atlantic Ocean to the east, tidal marshes to the west, Sapelo Sound to the south and St. Catherine's Sound to the north. The exact location of Mission Santa Catalina de Guale (circa A.D. 1580-1680) was unknown until 1979 when American Museum of Natural History crews found the site and began three decades of intensive excavations. The remains of the church, the convent and the mission kitchen have been partially excavated, but significant parts of each structure remain buried on site. Mission Santa Catalina de Guale is one of the most significant Spanish Colonial sites in North America, but 95% of the site remains unexcavated. The mission is situated in a dynamic landscape bounded by multiple meanders of a tidal creek and subjected in the past decade to substantial erosion. A model for landform dynamics has been built with the USGS Digital Shoreline Analysis System (DSAS) and data includes historical imagery and ground-collected GPS data. Shorelines were digitized based on the position of the cut bank or bluff that bounds the island core, adjacent marsh and active meander cut banks of Wamassee Creek. Uncertainties were incorporated directly into the model whereby more reliable data are given a greater weight or emphasis in determining a best-fit line under a weighted linear regression (WLR) method. The marsh and island core margin appeared relatively stable over the study period (1951-2013) with WLR rates ranging from 0.01 to 0.20 m/yr. In contrast, dynamics associated with the cut bank margin of the island core have resulted in relatively higher WLR rates of 0.20 to 1.4 m/yr and associated erosion and potential loss of archaeological materials. The more recent and accurate data (1999-2013) has been used to facilitate a predictive model that is incorporated into strategic planning to mitigate the loss of materials. The DSAS model has demonstrated proficiency at capturing landform changes associated with the mission site. The results have been incorporated into strategic planning efforts and the model offers the potential as a decision making tool at archaeological sites in similar physical settings.