Investigating Controls on Barrier Island Overwash and Evolution during Extreme Storms

Over short periods of time, extreme storms can significantly alter barrier island morphology, increasing the vulnerability of coastal habitats and communities relative to future storms. These impacts are complex and the result of interactions between oceanographic conditions and the geomorphic, geological, and ecological characteristics of the island. A 2D XBeach model was developed and compared to observations in order to study these interactions along an undeveloped barrier island near the landfall of Hurricane Florence in 2018. Beachface water levels during the storm were obtained from two cross-shore arrays of pressure sensors for comparison to model hydrodynamics. Aerial drone imagery was used to derive pre-storm and post-storm elevation data in order to quantify spatially varying erosion and overwash. Sediment grain size was measured in multiple locations, and we estimated spatially varying friction by using Sentinel-2 satellite imagery. The high spatial and temporal resolution of satellite imagery provided an efficient method for incorporating pre-storm spatially varying land cover. While previous studies have focused on the use of spatially varying friction, we found that the utilization of local median grain sizes and full directional wave spectra was critical to reproducing observed overwash extent.