Velocity predictions for shoaling and breaking waves with a Boussinesq-type model

In this paper, the performance of a 1-D Boussinesq model is evaluated again st laboratory data for its ability to predict surf zone velocity moments. W ave evolution over a plane beach and a complex bathymetry both extending in to the surf-zone is examined for six cases. For the plane beach, these comp rise two cases, a spilling and a plunging cnoidal wave. For the complex bat hymetry, these comprise four cases of longer and short wavelengths (spillin g and plunging breakers), with regular and irregular periodicity. The model evaluation places emphasis on parameters of the wave field that could be u sed for the prediction of sediment transport; orbital velocity, undertow, v elocity skewness, kurtosis and asymmetry. It is found that, despite an over estimation of the depth-averaged horizontal velocity in the regular waves c ases, the predicted higher order velocity moments and undertow are in good agreement with the laboratory data. A bispectral analysis demonstrates that the nonlinear transfers of energy amongst the low order harmonics are well reproduced, but energy exchanges with the higher harmonics are less well p redicted. As a result, the model handles velocity moments better in the sho rter wave tests than in the long wave cases where triad interactions are st ronger. Of the four parameters describing wave breaking, the model behaviou r is most sensitive to the critical wave front slope phi (B). especially wi th regard to velocity skewness and kurtosis predictions. It is also found t hat increasing the thickness of the surface roller for the case of plunging breakers improves the model's performance. (C) 2000 Elsevier Science B.V. All rights reserved.