Breach Evolution - Coastal System Change at Fire Island, New York Completed

Breach Evolution at Fire Island

Breaches in barrier islands play an important role in long-term island resilience by transferring sediment to the bay side of islands, which is one of the ways that barriers keep up with sea level rise. Breaches are also important for bay and barrier island ecosystem function, wherein tide and storm-driven flows flush bay water, increase salinity, dilute contaminants, and provide otherwise unavailable migration pathways for fish and other biota. In 2012, during Hurricane Sandy, a breach formed in the Otis Pike Fire Island High Dune Wilderness Area on Fire Island, NY. The breach changes are being monitored with collaborators at USACE, NPS, and SUNY-Stonybrook using a variety of observational techniques including single-beam bathymetry, aerial lidar, GPS elevations, and aerial imagery.

Sources/Usage: Public Domain.

From the time of its formation through the winter of 2015, the dominant change to the breach geomorphology was the recurring formation of a spit on the western side of the breach. The material forming the spit was eroded from the western ocean side of the barrier beach and transported northward along the western shoreline into the bay. Once formed, the spit restricted tidal flow exchange through the western flood shoal and correlated to a northeast-southwest orientation of the main breach channel.

USGS breach morphology observations have been used to develop a hydrodynamic and geomorphic numerical model, with collaborators at Deltares, which produces accurate hindcasts of the water levels in Great South Bay and breach evolution.  The model results are being used to evaluate the relative importance of various hydrodynamic forcings responsible for breach growth and stability.

Sources/Usage: Public Domain.