Barrier breaching versus overwash deposition: predicting the morphologic impact of storms on coastal barriers

Abstract:

Waves and water level setup during storms can move water and sediment across barrier islands. Overwashing flows can be depositional and form washover fans, but can also cause erosion and barrier island breaching. These widely different outcomes remain difficult to predict. Here we use the hydrologic and morphologic model Delft3D to understand the controlling factors of barrier breaching and washover deposition. We simulated different storm characteristics, barrier island morphologies, and types of dune vegetation. From these model simulations we developed a predictor for overwash volume and breaching potential. Model comparison against observations of 24 washovers and 4 breaches from hurricane Sandy show reasonable correspondence for natural but not for developed barrier islands. We suggest parameterizations for tidal inlet formation of overwash deposition that can be used for long-term barrier island models.