Modelling of hurricane impacts on US barrier islands

Barrier Islands protect mainland coastlines against storm impact and are themselves important as natural habitats, residential, and recreational areas. The need to quantitatively assess the vulnerability of these barrier islands to storm and hurricane impacts increases with rising sea levels and increasing probability of occurrence of higher storm surge levels.

An accurate prediction of barrier island response is challenging because of the complex interaction of hydro- and morphodynamic processes, such as erosion of dune faces by wave attack, formation of breaches by wave overwash and inundation, and erosion of channels by return flow from the bay to the ocean. These processes are controlled, in part, by the offshore water levels (surge and tide) and wave conditions, and by the initial topography of the barrier islands and characteristics such as sediment type and vegetation.

We provide an overview of the performance and sensitivities of the XBeach model for three cases of hurricane impact: the breaching of Fire Island (NY) due to hurricane Sandy, the breaching of Matanzas (FL) due to Hurricane Matthew, and the overwash near New River Inlet (NC) due to Hurricane Florence. For all three cases, high-quality pre-storm LIDAR and post-storm Structure for Motion topo-bathymetry was obtained by USGS, and high-resolution COAMPS meteorological forcing was provided. These inputs were used to drive the XBeach morphodynamical model.

We show by comparison with observations that the model is capable of predicting the overall dune erosion and sedimentation volumes correctly. The model also predicts the breaches and overwash in approximately the observed locations, but is sensitive to the vegetation roughness, the onshore sediment transport formulation, and the offshore hydrodynamic forcing.