Accurate surf zone modelling is a major interest in coastal engineering; given the high computational cost of solving
Navier-Stokes equations, shallow water theories – Boussinesq-type equations (BTEs) and nonlinear shallow water
equations (NSWEs)– remain relevant. BTEs are the most popular, because they account for both nonlinearity and
dispersion at different accuracy levels. However, Boussinesq models have a shortcoming: artificial techniques are
needed to simulate shoreline motion and wave breaking. Here a new treatment of wave breaking is proposed.
The 2DH Boussinesq equations of Madsen and Sørensen (1992) are solved by a FVM-FDM scheme. Wave breaking
modelling is based on two considerations: (1) in shallow waters, as breaking is approached, dispersion becomes
negligible compared to nonlinearity, hence, NSWEs are an appropriate approximation of the flow and can be solved
instead of Boussinesq equations; (2) when integrated by shock-capturing methods, NSWEs intrinsically represent the
propagation of bores, which are similar to spilling breakers. A criterion, based on such similarity and not subject to
calibration, is introduced to establish when the conditions for the application of NSWEs are achieved. Once NSWEs are
applied, wave breaking is automatically handled: wave height decay and mean water level setup emerge as parts of the
solution. Comparisons between numerical results and experimental data show that wave breaking and its effects on the
flow are accurately modelled; complexity and arbitrariness are limited with respect to traditional methodologies.