Non-homogeneous approximation for the kurtosis evolution of shoaling rogue waves

Abstract

Bathymetric changes have been experimentally shown to affect the occurrence of rogue waves. In view of the central role played by the excess kurtosis of the surface elevation in estimating rare event probabilities, we translate the recently determined evolution of the rogue wave probability over a shoal into that of the kurtosis. We provide an effective theory that connects the non-homogeneous correction to the spectral analysis and the evolution of excess kurtosis over the shoal, as well as the kurtosis upper bound. In intermediate water depth the vertical asymmetry between crests and troughs is virtually constant throughout the shoal for a given wave steepness and bandwidth, thus not affecting the exceedance probability. Conversely, a sharp increase in steepness increases the asymmetry for waves in intermediate depth. Thus, both the tail of the exceedance probability and excess kurtosis grow.