ABSTRACT

An airborne videotape mapping system was used to examine the impacts of Hurricanes Danny and Juan on the Isles Dernieres shoreline geomorphology in 1985. Videotape imagery was acquired in July 1984 and in July (pre-storm), August (post-Danny), and November (post-Juan) 1985. We developed a coastal geomorphic classification to map the spatial and temporal changes between surveys.

The Isles Dernieres barrier island arc is a low-profile, transgressive coastal feature. The central islands of the Isles Dernieres, Whiskey Island and Trinity Island, are the lowest in relief and elevation and have the least diverse habitats. Nonstorm morphology is predominately a combination of washover flats and higher dunes and washover terraces. Raccoon and East Islands, the ends of the Isles Dernieres, are higher in relief and elevation and have greater habitat diversity. Hurricane Danny's impact was representative of a rapid shore-normal impact by a minor force-1 hurricane. In general, landform relief on the Isles Dernieres was reduced slightly as a result of Hurricane Danny, which breached 7 major and 32 minor washover channels. After Hurricane Juan a total of 57 minor and 8 major washover channels were left and the higher-relief dunes, dune terraces, and washover terraces were destroyed. The primary morphology of the Isles Dernieres was reduced to and dominated by washover flats, intertidal flats, and other lower-relief landforms.

The spatial morphological variability of the Isles Dernieres indicates that the rate of shoreline change and the sediment supply control landform development. The temporal morphologic variability is a function of the frequency and magnitude of storm impacts and of sediment supply. The lower-relief landforms are more sensitive to storm impacts. Vegetation is important in reducing the effects of hurricanes. The barrier island restoration technique used at East Island effectively reduced erosion and preventing breaching.