XBEACH: A TOOL FOR ASSESSING THE VULNERABILITY OF BARRIER ISLANDS TO THE EFFECTS OF CLIMATE CHANGE

Effective management of barrier islands requires that the future impacts of sea-level rise and increased storminess be anticipated: assessing future vulnerability is necessary for adaptation planning and sustainable resilience. Application of the process-based numerical model, XBEACH, can evaluate the geomorphological response of beaches and dunes to the coastal processes associated with hurricanes and further exacerbated by higher sea level. XBEACH was validated by comparing the impacts of Hurricane Irma with those postdated by the model’s application on Keewaydin Island, an unmanaged and pristine barrier island along southwest Florida’s Gulf coast. Keewaydin sits within the Rookery Bay National Estuarine Research Reserve, has never been renourished, and has responded to natural processes without human intervention. Consequently, the island’s response to climate change serves as a natural exemplar. Irma was a Category 3 hurricane which made landfall on September 10, 2017 approximately 4 miles south of the Keewaydin Island’s southern terminus. The island experienced extensive overwash and one dune breach occurred 3 km from southern end. As the hurricane-generated waves came at an oblique angle to the shoreline, the morphological impact decreased to the north, away from the landfall location. The model was implemented on a high-resolution grid (2m across-shore), with resolution decreasing progressively in the offshore direction. Waves and storm surge data from a coupled hydrodynamic model (CH3D-SWAN) were used to force the XBEACH simulation. The model was fine-tuned with the help of the shield’s parameter, wave asymmetry, and skewness. XBEACH successfully simulated foredune erosion and overwash from the combined action of storm surge and waves and the impact of the storm shows lesser influence in the northward direction. The model will now be employed by Collier County for the entire length of its coast.