GEOLOGIC FRAMEWORK CONTROLS ON ISLAND RESPONSE TO AND RECOVERY FROM EXTREME STORMS

This paper examines the multi-scale feedback relationship of event-scale sediment exchange between beach and dune with long-term barrier island response to extreme storms and recovery from those storms. Using field and remotely sensed data from Santa Rosa Island in northwest Florida and South Padre Island in Texas, it is shown how the alongshore variation in storm washover and breaching is coherent (but in different ways) with transverse ridges that developed on the inner-shelf as the island transgressed. Model results suggest that the ridges are reinforced during tropical storms and hurricanes through the offshore transport of beach and dune sediment eroded by the storm surge. These ridges force an alongshore variation in beach and nearshore state that determines the aeolian transport potential and available sediment supplied from beach to dune. On Santa Rosa Island, dune aeolian transport and dune heights are limited by the steep beachface, such that the largest dunes are found at the crest of the transverse ridges where the beachface is more intermediate. In contrast, Aeolian transport and dune heights are shown to be supply limited on Padre Island, which has a relatively dissipative nearshore and beach. The largest dunes on Padre Island are found between transverse ridges where the profile is more intermediate and sediment is more readily supplied by inter- and supra-tidal swash bars. As a consequence, the largest storm surge and washover occurs at the transverse ridges where the dunes are small, while on Santa Rosa Island, the storm surge is greater where the dunes are larger leading to greater loss of sediment offshore. While Padre Island and Santa Rosa Island represent different beach states and exhibit different mechanisms of beach-dune interaction and storm impact, it is shown that small-scale beach-dune interaction is as much dependent on the geologic framework of the island, which developed as it transgressed, as the transgression and storm response are dependent on the exchange of sediment between beach and dune.