Runups of unusual size: rogueness and variability of swash

The occurrence of swash larger than those predicted by the Rayleigh distribution is examined using a phase-resolved numerical model. Multiple realizations of spectral boundary conditions and beach configurations are considered in the analysis. Planar beaches characterized by surf similarity parameters between 0.3 and 0.6 are found to be more likely to produce unusually large swash. Maximum runup is found to correlate with the maximum infragravity (IG) wave height at the location of swash initiation, the landwardmost continuously wet point. The analysis is extended to beaches with bilinear profiles, where the foreshore slope is steeper than the shoaling slope. It is found that the still water level plays a controlling role in the magnitude of large swash. For these beaches it is found that the still water level with respect to the beach toe influences both the IG and shortwave height at swash initiation. Similar to the planar beach case, swash is found to be maximized when the sum of both IG and shortwave height is maximum; this occurs at toe depths 2-3 times the offshore significant wave height.