SWASH ON A GENTLY SLOPING BEACH

Waves observed in the inner surf and swash zones of a fine grained, ge ntly sloping beach are modeled accurately with the nonlinear shallow w ater equations. The model is initialized with observations from pressu re and current sensors collocated about 50 m from the mean shoreline i n about 1 m depth, and model predictions are compared to pressure fluc tuations measured at five shoreward locations and to run-up. Run-up wa s measured with a vertical stack of five wires supported parallel to a nd above the beach face at elevations of 5, 10, 15, 20, and 25 cm. Eac h 60-m-long run-up wire yields time series of the most shoreward locat ion where the water depth exceeds the wire elevation. As noted previou sly, run-up measurements are sensitive to the wire elevation owing to thin run-up tongues not measured by the more elevated wires. As the wi re elevation increases, the measured mean run-up location moves seawar d, low-frequency (infragravity) energy decreases, and higher-frequency sea swell energy increases. These trends, as well as the variation of wave spectra and shapes (e.g., wave skewness) across the inner surf z one, are well predicted by the numerical model.