QUANTIFYING ANTHROPOGENICALLY-DRIVEN MORPHOLOGIC CHANGES ON A BARRIER ISLAND: FIRE ISLAND NATIONAL SEASHORE, NEW YORK

Beach scraping, beach replenishment, and the presence of moderate development have altered the morphology of the dune/beach system at Fire Island National Seashore, located on a barrier island on the south coast of Long Island, New York. Seventeen communities are interspersed between sections of undeveloped land within the park boundary. To assess the extent of anthropogenic influence, volume change, shoreline change, and changes to beach profile morphology were analyzed at an eastern and a western study site, each ~4 km long. Each site contains both modified (developed and scraped) and natural areas. Lidar, RTK GPS, and beach profile datasets were utilized to assess morphological change at two scales; the individual community (<1 km) and over each study site (4 km). Shoreline change was calculated from 1979 to 2007, as well as for individual decades within the 28-year period. Beach and dune volume change was assessed between 1998 and 2007. The beach profile datasets range in duration from 1996 to 2006.

The results indicate that along relatively sediment-poor areas of the island, locations backed by development experienced more shoreline erosion and volumetric loss, on a decadal time scale, as compared with adjacent undeveloped areas. In more sediment-rich areas, volume increases are spatially and temporally consistent with sand replenishment activities. The more detailed community-scale beach profile analysis shows distinct morphological differences in scraped areas relative to non-scraped areas of the beach. In general, scraped areas where shoreline erosion rates are highest also have lower dune elevations, resulting in a higher likelihood of overwash during storm events. In more volumetrically stable areas, the rapid mobilization of material from the anthropogenic (scraped) dune results in increased beach accretion downcoast.

National park lands are immediately adjacent to developed areas on Fire Island, and even relatively small human-induced modifications can impact park resources and beach/dune response to storms. This study is the first to conduct a systematic analysis on how anthropogenic modifications impact resources at Fire Island National Seashore, and provides essential information for effective management and preservation of coastal resources within the park.