Morphodynamic modelling of the Fire Island Wilderness Breach

The Wilderness Breach, located within the Otis Pike High Dunes Federal Wilderness Area on Fire Island, NY, was formed during Hurricane Sandy in October 2012 and has remained open, providing a rare opportunity to study the morphologic evolution of a natural breach. Numerical models were used to hindcast the morphodynamic changes since October 2012 in order to gain a better understanding of the processes that govern breach evolution. The model results were compared against repeat bathymetric surveys and aerial imagery. The best match with observations was obtained when using a combination of Delft3D (for calm conditions) and XBeach (for storms) models. The results show a rapid initial growth and westward migration of the breach, apparently caused by a series of storm events in the winter of 2012-2013. Approximately 18 months after formation, breach morphology is governed by seasonal conditions, and the rate of growth has declined substantially. Results provide insights on natural breach evolution that can be used to inform the management of breaches caused by future storm events.