The First Guess: Testing predictions of coastal change from shoreline orientation and wave climate along Cape Cod and the U.S. Eastern Coast

Abstract:

Myriad factors, including sea-level rise, cross-shore sediment transport, tidal inlet mechanics, geological inheritance, and, more recently, anthropogenic activities affect the shape and rates of change of the shoreline. However, the generally smooth shape of many sandy shorelines provides a rather clear demonstration that alongshore sediment transport, through gradients in this flux, exerts a first-order control on coastal shape. Fisher (1968) has also previously observed that the mid-to-northern USA coast, spanning the Cape Cod, Long Island, New Jersey, and Delmarva shores, share many basic traits, as they are comprised of a series of erosional headlands flanked by accretionary spits and, towards their southern/western extension, increasingly disjointed barrier island chains. Here, using ~30-year hindcast wave data and modern shoreline orientations, we test the first-order prediction that alongshore sediment transport drives the long-term evolution of the shorelines of these systems. We find that, in many cases, predictions of erosion and accretion from shoreline orientation and wave climate alone match historical trends in shoreline change. These first-order predictions, however, do not explain all of the historical shoreline changes, and our analysis can highlight the regions where other processes must be invoked to understand long-term shoreline change. However, we find that changes to the shoreline orientation are sufficient to explain many well-documented locations of rapid shoreline change, further suggesting that in these locations geologic and cross-shore controls may be playing secondary roles in shoreline change.