Morphodynamic evolution of a natural Inlet

Barrier island breaches often form when low-lying areas become inundated during large storms. Breaching plays a vital role in barrier island response to sea-level rise by depositing sediment into the back bay. However, because breaches often close naturally or mechanically, there is limited information about the processes that lead to stability (e.g., transition to inlet) or closure. In October 2012, the wave and storm surge associated with Hurricane Sandy resulted a barrier breach within the Otis Pike Fire Island High Dune Wilderness on Fire Island, NY. The breach formed within a federally protected wilderness area preventing mechanical closure, thereby providing an opportunity to study its morphologic evolution and the processes that drive it. The wilderness inlet has been extensively monitored through a combination of GPS topography, single-beam bathymetry, lidar topobathy, aerial imagery, and satellite imagery. Our analysis indicates that the initial 50-m wide breach rapidly grew in the first 6 months and continued to grow at a slower rate for the next year before reaching a quasi-equilibrium state. Seasonal hydrodynamic changes result in a cyclic change to inlet geomorphology, typically widening of the breach in the calmer late spring and summer months followed by a decrease in width in the more energetic fall and winter months. Until 2018, the eastern inlet shoreline remained relatively stable but has since propagated westward. The inlet has further resulted in a disruption of the down-drift sediment transport resulting in sustained shoreline erosion up to 4km from the inlet. The results of this study focus on the processes responsible for the temporal and spatial evolution of a natural inlet system and the spatial impact on the adjacent shoreline which is important in predicting the best management response to future breaches.