Hindcasting Potential Hurricane Impacts on Rapidly Changing Barrier Islands

Hindcasts of the coastal impact of Hurricane Ivan on Santa Rosa Island, Florida, using a storm-impact scaling model that compares hurricane-induced water levels to local dune morphology, were found to have an accuracy of 68% in predicting the occurrence of one of four impact regimes: swash, collision, overwash, and inundation. Errors were overwhelming under-predictions of the regime where the observed response was more extreme than had been expected. This is related to the evolution of the profile during the storm. Mean pre-storm dune elevations decreased by 1.9 m over the 75-km long island as most of the dunes were completely eroded during the storm. Dramatic morphologic change during a hurricane makes barrier islands more vulnerable to overwash and inundation than will be predicted based on pre-storm dune parameters. Incorporation of the timing of rising water levels relative to storm-induced profile evolution is required to improve model accuracy.