BEACH EROSION AND GEOMORPHOLOGY: ASSESSING CORRELATIONS BETWEEN BEACH AND NEARSHORE MORPHODYNAMICS

Accurate prediction of beach response to storms requires synthesizing complex relationships between nearshore hydrodynamics, underlying geology, nearshore bathymetry, beach topography, and sediment characteristics. Previous research on the Outer Banks of North Carolina has correlated the presence of underlying paleo-channels, nearshore heterogeneous sediment, and shore-oblique bars with shoreline erosional hotspots. Current research also suggests that undulations in the shape of the shoreline (megacusps and embayments on the scale of 1000m) may be related to the nearshore shore-oblique bars and have been shown to persist throughout storm events. Despite the documented relationships between these features, the morphodynamic link between the persistent nearshore bathymetry, shoreline morphology, and long-term erosion is unknown. This study presents detailed measurements of beach topography and grain size on two embayments and a megacusp during an extra-tropical storm along the Kitty Hawk, NC erosional hotspot, and aims to quantify spatial variations in beach response to storm events.

Analyses of topographic changes between a summer beach profile and a winter nor'Easter profile show erosion of the foreshore and accretion on the upper beach. Erosion of the foreshore is consistent with offshore movement of the summer berm, whereas the accretion at the dune toe may be due to dune slumping during the storm or beach scraping. A prominent scarp was observed in the post-storm data where the flat summer backshore was previously located. Initial results indicate little difference between the topographic response of the megacusp compared to the embayments during the storm event. Preliminary analyses of post-storm beach sediment suggest that spatial variations in grain size exist along the beach with sediment more poorly sorted in the embayments versus the megacusps. Temporal variations (pre- and post-storm) in grain size from the embayments and megacusp will be investigated for statistically significant differences. Alongshore variations in energy dissipation will also be quantified from Bar and Swash Imaging Radar (BASIR), and used in conjunction with beach topography and grain size data to create a conceptual model of beach response to storms along this erosional hotspot.