Wave dissipation on counter current in SWAN

Recent hindcast studieshave shown the significant influence fo currents on the prediction of wave fields in the Amelander Zeegat tidal inlet. In following current, observations are typically well reproduced, but under strong opposing (near-blocking) current, wave heights are significantly overestimated. This strongly affects the reliability with which these predictions can be applied in the assessment of safety from flooding. The present study aims to develop a formulation for the dissipation of wave on adverse currents that is suitable for both mature wave fields and young wind sea conditions, and to validate it for a range of field situations. A new formulation for the enhanced dissipation of waves on a counter current is proposed which is based on the saturarion-based formulation of Van der Westhuysen et al. (2007), and scaled with the degree fo Doppler shifting per spectral component. This expression contains one additional unknow parameter, which was calibrated using laboratory and field obervations. Application of this enhanced dissipation term for a data set of Amelander Zeegat field cases show an improvement for opposing current situations in the tidal channel. For situations with following current, no deterioration of results is found. In particular, the result for the young wind sea on the tidal flats are not significantly affected, unlike with the expression of Ris and Holthuijsen (1996). Therefore, in principle, it is recommended to apply this formulation to simulations in the Wadden Sea. However, it is recommended to further validate the proposed model using further data sets.