What a difference a beach makes. Hydrodynamic modeling and validation of wave overtopping flooding at two southern California beaches.

Beaches mitigate urban coastal vulnerability. A field validated hydrodynamic modeling methodology is applied at two southern California sites to evaluate the effect of different beach profiles on overtopping and backshore flooding. SWAN, a numerical wave model, transformed deep water buoy spectra to the nearshore. XBeach is parameterized with a decade of aerial LiDAR (1998-2009) and quarterly beach surveys to estimate temporally variable overflow rates. A two dimensional nonlinear shallow water model resolves overland flow, urban features and storm system drainage. Results show beach state is critical to accurate backshore flood prediction. Additionally, management practice such as nourishment and berming significantly affect flooding outcomes.