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 engineeringpurposes, they can be described by simple parameterizations that allow their easier inclusion in nearshoremorphodynamic models. Most existing parameterizations propose the estimation of velocity nonlinearities onlyfrom local wave parameters (such as the Ursell number). Herein, it is demonstrated that this providesinaccurate estimations of the wave nonlinearities. Furthermore, the effect of offshore wave steepness, offshorespectral bandwidth and beach slope on the velocity nonlinearities is shown to be sufficiently important to meritits inclusion in the existing parameterizations. Ruessink et al. (2012) [28] parameterization is modified in orderto include both offshore spectral bandwidth and a new parameter, NP 0 , which takes into account the beach slopeand 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 (nearbreaking) that contribute the most for sediment transport.