Depth induced breaking of wind generated surface gravity waves in Estonian coastal waters

Depth-induced wave breaking is a key term for wave energy dissipation in the action balance equation of the third generation spectral wave models, and becomes an essential consideration in modelling wave behaviour in shallow water and near the coast. Neglecting this sink function leads to an overestimation of significant wave heights. Current paper addresses the importance of depth induced wave breaking, using the SWAN wave model, at two locations in Estonian coastal waters in case of NNW storms — the first site is the Harilaiu Bank, situated in the north-west of the Saaremaa Island while the other one is Tallinn Bay. We performed simulations using SWAN with two different setups, i.e. the depth induced wave-breaking accounted and not accounted. The computed wave height in the first case was smaller than in the second case with maximum difference of 4.8 m in the Harilaiu Bank and 2.3 m in Tallinn Bay. Previous studies using the WAM model suggest that remarkable wave maxima exist in these regions due to focusing of wave rays e.g. due to topographic refraction of surface waves. As these maxima were reproduced by SWAN when depth-induced wave breaking was turned-off, we conclude that the maxima simulated by WAM can be an artefact of the model.