Barrier Island Breaching in Response to Extreme Storms: Morphodynamic Evolution of the Fire Island Wilderness Breach

Barrier islands evolve and move landward in response to rising sea levels by transport of sediment from the ocean to the estuarine coast. One mechanism for this redistribution of sediment is the formation of island breaches. Breaches are generally ephemeral features and close through natural processes; those that do not close naturally are often filled to protect coastal infrastructure. As a result, there is limited understanding of the morphodynamics and natural evolution of breach systems.

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. Bathymetric data from repeat surveys, shoreline positions, aerial imagery, wave buoy observations, and meteorological measurements were used to characterize the temporal and spatial evolution of breach morphology (width, shape, shoreline migration rate, volume, channel depth, orientation, etc.). Our analysis indicates that the initially 50-m-wide breach, grew rapidly as the western shoreline migrated. Sediment redistribution resulted in the development of a well-defined ebb delta and an extensive flood-shoal complex. Approximately 18 months after formation, breach morphology is governed by seasonal conditions, and the rate of growth has declined substantially. The use of various morphometrics has allowed for the development of a conceptual model of breach dynamics, which can be compared to a numerical morphologic model of the breach to assess model performance. Results provide insights on natural breach evolution that can be used to inform the management of breaches caused by future storm events.