Non-linear propagation of unidirectional wave fields over varying topography

The present study aims at investigating the non-linear triad interaction pr ocess affecting shoaling surface gravity wave fields. The triad interaction phenomenon being enhanced towards the shore, the domain of study is extend ed up to the surf zone. Three 1D non-linear wave models (one phase-resolvin g and two phase-averaged spectral models) have been, implemented and compar ed to laboratory experiments performed in a wave flume. This set of models includes two existing models and a new one which has been developed in the frame of this work. The models include a breaking dissipation term based on the parametrical model of Battles and Janssen [Battjes, J.A., Janssen, P.A .E.M., 1978. Energy loss and set-up due to breaking of random waves. Proc. 16th Int. Conf. Coastal Eng. (ASCE), Vol. 1, pp. 569-587.]. The investigati ons concern the evolution of variance spectra, spectral significant wave he ight and mean period over a barred bathymetric profile. In addition, the pe rformances of the different models are analysed by computing the spectral s ource term for triad interactions. We found that all models are able to rep roduce the main features of non-linear mechanisms affecting a wave field in the near-shore zone. The phase-resolving model gives the most accurate res ults for non-breaking situations. It correctly reproduces the non-linear co upling effect in decreasing water depths due to wave-wave interactions, as well as the harmonic release after a bar. However, the model is computation ally time-consuming. The CPU time is considerably reduced using phase-avera ged models. They give satisfactorily results on harmonic generation. Howeve r, they do not reproduce the release of harmonics as water depth increases. In breaking conditions, the variance spectra undergo significant changes u nder the combined effects of non-linear energy transfers and dissipation. T he depth-induced wave breaking model included in thr equations provides a g ood estimate of the energy decay in the surf zone. (C) 1999 Elsevier Scienc e B.V. All rights reserved.