IMPROVED MODELLING OF WAVE-CURRENT INTERACTION IN SWAN

Abstract

Recent hindcast studies in the Amelander Zeegat tidal inlet in the Dutch Wadden Sea have shown the significant influence of currents on the prediction of wave fields by the spectral wave model SWAN. In following current, observations are typically well reproduced, but under strong opposing current, wave heights are significantly overestimated. Ris and Holthuijsen (1996) propose that such overestimations are due to insufficient steepness dissipation of waves on an opposing current gradient. The present paper presents a new formulation for the enhanced dissipation of waves on a counter current gradient which is scaled with the degree of Doppler shifting, and hence steepness increase, due to the current. This expression contains one additional unknown parameter, which is calibrated using laboratory observations. This formulation is suitable for both mature wave fields and young wind sea conditions. Application of this enhanced dissipation term to a data set of Amelander Zeegat field cases shows an improvement for opposing current situations in the tidal channel. For following current, no significant deterioration of results is found. In particular, the results for the young wind sea on the tidal flats are not significantly affected, unlike with the Ris and Holthuijsen (1996) expression.