Shoreline dynamics and environmental change under the modern marine transgression: St. Catherines Island, Georgia, USA

The current study evaluated shoreline dynamics and environmental change at St. Catherines Island, Georgia, with attention to the two major controls of barrier island formation and modification processes. The major controls are the rate of sea level rise for the Georgia Bight which has remained constant in twentieth and twenty-first century tide gauge data and dynamically changing rates of sediment supply based on anthropogenic modifications to land cover and fluvial systems that are reflected in sediment mass flux to the southeastern US coast. The island is dependent on the net longshore transport of sediment from the north and the closest fluvial system with appreciable discharge is the Savannah River. The evaluation of anthropogenic modifications to the rate of sediment supply within the Savannah River watershed indicates that in spite of significant changes in sediment flux rates of +300 % in 1859–1951 (the pre-dam era) and −20 % in 1951–2014 (the post-dam era), shoreline retreat on St. Catherines Island was continuous during the study period with a significant acceleration of shoreline retreat observed with spit and berm landforms during the modern or post-dam era. The apparent acceleration in the shoreline retreat rates for the spit and berm landforms is indicated as an inflection point in time-series plots of data. The change in shoreline retreat rates for the spits and berms correlates with the timing of major disruptions in the rate of sediment supply to the coast of Georgia, specifically the placement of the initial impoundments on the major rivers of the southeastern US.