Evaluating XBeach performance for extreme offshore-directed sediment transport events on a dissipative beach

The performance of the process-based nearshore model XBeach for predicting extreme offshore-directed sediment transport was investigated using field observations at a dissipative beach in Japan. Three extreme erosion events were identified from a record of 6,209 observations of the cross-shore profile change at Hasaki, Japan, from 1987 to 2003. The analysis considered the sensitivity of the wave nonlinearity of short waves that could be tuned using the parameter, f(ua), to the observed bed profile change. The comparisons revealed that for extreme offshore-directed sediment transport events, f(ua) = 0.0 is the best fit for predicting these extreme beach profile changes. In the nearshore zone, erosion was underestimated, and the BSS exhibited low values. Peak sediment deposition occurred in the bar-offshore zone with sediments transported from the nearshore zone and was estimated by the model reasonably well. In addition to the three extreme events, 14 other large events were identified, and the trends of beach profile change could be estimated with sufficient tuning of the f(ua) parameter. After analyzing the correlation between f(ua) and wave and morphology-related parameters, the f(ua) value could be correlated to the observed volume change. This suggested that if there were a rough estimate of the expected total volume change, this may help in setting f(ua) value.