Modeling Saltwater Intrusion in a Migrating Barrier Island

One of the major natural responses to global warming is sea-level rise. Rise in sea-level can affect coastal barrier islands in two ways; i) geomorphologically, by changing the shape of the islands and ii) hydrogeologically, by initiating saltwater intrusion into the island aquifer, thereby reducing freshwater resources. As the shape of the freshwater lens in an island aquifer is characterized by the geometry of the island itself, any morphological change would also alter the lens' shape. Sea-level rise will create transgressive sequences of deposits. This will result in heterogeneous zones of hydraulic conductivity. It is thus of interest to investigate the roles these coupled responses play in controlling saltwater intrusion in a barrier island setting. For this purpose, we use numerical modeling with SEAWAT to simulate saltwater intrusion in Caladesi Island, a migrating barrier island on the Gulf coast of Mexico. Caladesi Island has shown considerable migration from 1883 to its present position. The southern end of the island undergoes erosion while accretion occurs at the northern end. We use theoretical geomorphic models of the island that may result as a consequence of predicted sea-level rise (according to IPCC Climate Change 2007, Synthesis Report). As previous saltwater intrusion studies in other islands have indicated, we expect to see landward movement of the freshwater-saltwater interface as a result of climate change induced sea-level rise.