Surfzone Setup and Alongshore Currents During Hurricane Matthew

The effect of winds on the setup (the increase of the mean water level owing to breaking waves in shallow water close to the beach) and on the alongshore surfzone flows during the passage of Hurricane Matthew (Oct 9, 2016) is investigated with observations and one dimensional numerical models (neglecting alongshore variability). Waves, mean flows, winds, and water levels were measured for 7 days between the beach and 11-m water depth at the USACE Field Research Facility near Duck, NC. Bathymetry was measured before and after the storm. During the peak of the storm, wave heights in 17-m water depth reached 5 m, setup was O(1 m), and alongshore flows (O(1 m/s)) reversed direction as the storm passed. Including wind in the models reduces modeled setup and alongshore flow errors up to 10% and 25%, respectively. The setup model is most accurate during the storm, and underpredicts the observations before and after the storm. The flow model underpredicts the velocities, but predicts the timing of flow reversal accurately. Using a wave transformation model and Snell’s law initialized with observations in 11 m depth to drive the models, rather than using the waves observed across the region, does not improve the results significantly.