DISPLACEMENT AND RECOVERY: THE POST-HURRICANE SANDY GEOMORPHOLOGICAL EVOLUTION OF THE FORT TILDEN SITE, GATEWAY NATIONAL RECREATION AREA

The Fort Tilden site is located within the National Park situated on the Rockaway barrier island, New York City, and it was impacted by the storm surge and waves associated with Hurricane Sandy in late October 2012. In the decades prior to Hurricane Sandy, considerable efforts had been made to stabilize the shoreline, including 41 groins, a wooden bulkhead, and a rock revetment in front of a coastal road (Shore Road) that ran the length of Fort Tilden. The road provided convenient access to the beach for the park users. With the engineered structures, the site had a history of variable erosion and accretion.

Hurricane Sandy caused major erosion of the beach and adjacent foredune, as well as the creation of washover deposits in low-lying areas at the western margin. Foredune displacement was as great as 50 m, with volume losses reaching 75 m³/m. Shore Road was destroyed for nearly 60% of its length.

The purpose of this research was to assess the rate and distribution of the recovery within eleven beach-dune compartments defined by specifically-selected groins. Considering the east to west direction of alongshore transport, the spatial distribution of the recovery responded to the Sandy-emplaced offshore sediments as well as the post-storm replenishment of over 2 million m³ pumped to the updrift beaches. Compared to a November 2012 LiDAR-derived DEM, the greatest post-Storm (spring 2015) volumetric gains were in the eastern compartment, decreasing westward. Moreover, the bulkhead presented an additional variable affecting transport and storage. Segregating the compartments into segments defined by position landward or seaward of the bulkhead revealed detailed patterns of recovery. Considering the span of over two years post-Sandy, the beach accreted beyond its pre-Sandy location in the east, gaining as much as 31 m³/m seaward of the bulkhead and decreasing to a loss of 20 m³/m at the west. Inland of the bulkhead, the comparisons to pre-Sandy showed that volume losses varied from -74 m³/m in the east, to -12 m³/m in the middle portion, to -30 m³/m to the west. The position of the foredune crestline had not changed since Sandy and the present upper portion of the profile may have established a new equilibrium position.