LINKING THE WAVE CLIMATE WITH MULTI-DECADAL ASSESSMENT OF MORPHOLOGIC CHANGE

Storm-driven morphologic changes to dunes and beaches are largely determined by the wave climate and existing morphologic state of the coastal system. Event-driven storm impacts are well-studied and modeled, however, the cumulative impacts and resulting vulnerabilities of multiple storms over decadal periods and longer are not as well documented. Using an existing and vetted run-up model, this study explores connections between wave processes and morphologic changes measured from historical topography and lidar surveys at 10, 30, and 40-year intervals on Fire Island, New York. Fire Island, a barrier island that lies along the south shore of central Long Island, has established morphologic differences in eastern and western reaches that have largely been attributed to variations in development and anthropogenic modifications, sediment supply along coast, and variations in incident forcing due to differences in offshore bathymetry and inner shelf geology. Our results show that spatial patterns of change are persistent over all intervals studied and appear linked with differences in geology, geomorphology, and land use. There is also a demonstrated correlation between zonal patterns of change and variations in the wave climate, which may in part be due to variability in nearshore wave conditions as a result of transformation from the site of measurement. In the eastern reach of the island, a substantial landward translation of the dune-beach profile is evident over the 40-year period. Strong correlations exist between model-identified locations likely to overwash and observed elevation changes of the dune crestline. This relationship verifies that total water levels during storms have exceeded dune crest elevations, implying that overwash is a strong contributor to landward migration in the eastern reach. The western reach also shows persistent likelihood of overwash, but in contrast to the eastern reach, shows limited landward translation of the profile, particularly in developed and modified areas. These results suggest that although the offshore wave climate is likely to exert some control on the dune-beach response over several decades, other factors such as human influences, sediment transport, and geologic variations in the system may override the wave response signal in the western reach.