COASTAL DUNE RECOVERY AND SHORELINE EVOLUTION IN RESPONSE TO STORMS ALONG EASTERN PERDIDO KEY, NW FLORIDA

This investigation quantified volumetric and morphologic change over a 36-year period in coastal dunes along both developed and undeveloped portions of eastern Perdido Key (PK), northwest Florida. Geographic information system (GIS) tools were used to quantify and analyze airborne LIDAR and ground-survey profile data for the subaerial foreshore and backshore of the island. The data, collected from 1974 to 2010, represents one of the more comprehensive databases that have been developed for analyzing sand transport and shoreline change along a barrier island. Results show that during periods of storm quiescence, dunes accrete and profile adjustment, whether landward or seaward, is strongly correlated to long-term trends in shoreline change. During the period under investigation, shoreline evolution was dominated by retreat related to natural erosional processes and human activity. The analysis revealed that overwash, resulting from elevated storm surge associated with five storm seasons during the study period, caused severe erosion of the foredune complex. This was especially true in regions where the island was narrow and the coastal dune field was discontinuous. While individual storm intensity is a good indicator of possible beach and dune profile alteration, the occurrence of a closely spaced cluster of storms is perhaps the most important metric in quantifying coastal change. The investigation also revealed that the maintenance of viable dune fields is dependent on several ancillary factors. Such factors include: sediment supply via longshore drift or artificial nourishment, island width, dune field width, continuity of the dune complex, and inner-shelf bathymetry.

Net volume loss of the foredunes was calculated at seven of the eight locations where profiles were measured. The greatest volume loss coincided with the presence of upland infrastructure along an unnourished beach. In areas where nourishment had taken place, foredune volumetric loss was significantly less pronounced. Dune sediment volume loss was lowest for the undeveloped, unnourished portion of the beach and averaged -4.9 ft³/yr per lateral meter.