GEOMORPHOLOGICAL MAPS AS A TOOL TO TRACK CHANGE: METRICS OF IMPACTS OF HURRICANE SANDY AT FIRE ISLAND NATIONAL SEASHORE

As entities, the coastal geomorphological maps of Fire Island National Seashore are spatial representations of the boundaries of surficial forms assigned to particular geomorphological categories. However, because the maps are based on the geophysical processes operating on the surface and sequence of landform development, they also represent temporally-defined stages in the evolution of the barrier island and are inherently powerful tools to track geomorphological change.

In the case of Fire Island National Seashore, a very detailed geomorphological map was constructed utilizing orthophotos and LiDAR data sets collected in 2011, and a second map was created based on orthophotos and LiDAR collected in November 2012, immediately following Hurricane Sandy. Because the two temporally-assigned maps used the same methodology to delineate the spatial dimensions of the geomorphological features and possessed a topographical quantity inherited from the LiDAR, they offer the opportunity to develop and track multi-dimensional metrics of the changes.

For comparisons of linear features such as a shoreline, the base of a dune, or a crestline, etc., a 1D measure of displacement for the time interval can be derived and calculated for some segment of Fire Island, or for the entire island. For 2D areal measures of beach, or foredune ridge, or depression, or wetland, etc., polygons of the specific feature can be determined for some spatial segment and comparisons made. The 3D comparisons are made for specific features, such as foredune volume, and depicted for segments of Fire Island. Placed in the context of the physical processes associated with Hurricane Sandy, the vectors of change are related to an understanding of the continued geomorphological evolution of Fire Island and are also of value in comparing outcomes of land management strategies among the variety of residential communities and the local, state, and federal agencies.