Improving the parameterization of wave nonlinearities - The importance of wave steepness, spectral bandwidth and beach slope

Wave-velocity nonlinearities are among the main drivers of sediment transport. For practical engineering purposes, they can be described by simple parameterizations that allow their easier inclusion in nearshore morphodynamic models. Most existing parameterizations propose the estimation of velocity nonlinearities only from local wave parameters (such as the Ursell number). Herein, it is demonstrated that this provides inaccurate estimations of the wave nonlinearities. Furthermore, the effect of offshore wave steepness, offshore spectral bandwidth and beach slope on the velocity nonlinearities is shown to be sufficiently important to merit its inclusion in the existing parameterizations. Ruessink et al. (2012) [28] parameterization is modified in order to include both offshore spectral bandwidth and a new parameter, NP0, which takes into account the beach slope and the squared offshore wave steepness. The new parameterization results in a reduction of the wave-nonlinearities estimation error of more than 50%, particularly for the maximum values of nonlinearity (near breaking) that contribute the most for sediment transport.