TRENDS OF DUNE CREST DISPLACEMENT 1976-2012, FIRE ISLAND, NEW YORK
Revisiting previous analyses of dune crest migration at Fire Island dating to 1976, beach/dune profiles, stereo pair orthophotos, and LiDAR elevation datasets were examined to derive dune crest locations. The several data sources provided feedback confirming results where they overlapped. A mean displacement of -25 m from 1976 to 2012 was calculated for the length of the island between Robert Moses State Park and Moriches Inlet, including maximum landward and seaward displacements of 175 m and 111 m, respectively. Periodic erosion and accretion were observed within that time, with particularly large fluctuations occurring as a result of the 1992 storms and subsequent replacements/replenishments. Between 2000 and 2011, the mean crestline displacement was approximately 1 m seaward for the entire length of the island and the largest landward vectors were located in the Old Inlet area; a location that subsequently breached under the stress of Hurricane Sandy. Sandy accounted for an average displacement of -15 m along the entire island. The foredune crest was almost systematically eliminated by the storm, either replaced in form and function by a secondary dune that was previously situated landward of the active foredune or eliminated entirely as a result of overwash. Approximately 17% of the foredune was eliminated without replacement.