Abstract: A nonlinear, short-wave-averaged model of surf beat, which describes essentially long-period motions associated with the mean free surface,is presented. The numerical techniques used in the solution are based on so-called Weighted-Average Flux (WAF) method, with Time-Operator-Splitting (TOS) used for the treatment of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modelling breaking long waves. The short wave (or primary-wave) energy e...