Coastal flooding: impact of waves on storm surge during extremes. A case study for the German Bight

Abstract

This study addresses impact of wind, waves, tidal forcing and baroclinicity on the sea level of the German Bight during extremes. The role of waves-induced processes, tides and baroclinicity is quantified and the results are compared with observational data that include various in-situ measurements as well as satellite data. A coupled, high-resolution, model system is used to simulate the wind waves, water level and three-dimensional hydrodynamics. The effects of the wind waves on sea level variability are studied accounting for wave-dependent stress, wave-breaking parameterization and wave-induced effects on vertical mixing. The analyses of the coupled model results reveal a closer match with observations than for the stand-alone circulation model, especially during the extreme storm Xaver in December 2013. The predicted surge of the coupled model enhances significantly during extremes when considering wave-current interaction processes. The wave-dependent approach yields to a contribution of more than 30 % in some coastal area during extremes. The improved skill resulting from the new developments justifies further use of coupled wave and three dimensional circulation models for improvement of coastal flooding predictions.