Joanna Staneva, Kathrin Wahle, Wolfgang Koch, Arno Behrens, Luciana Fenoglio-Marc and Emil V. Stanev: Coastal flooding: impact of waves on storm surge during extremes – a case study for the German Bight. Nat. Hazards Earth Syst. Sci., 16, 2373-2389, doi:10.5194/nhess-16-2373-2016


This study addresses the impact of wind, waves, tidal forcing and baroclinicity on the sea level of the German Bight during extreme storm events. The role of wave-induced processes, tides and baroclinicity is quantified, and the results are compared with in situ measurements and satellite data. A coupled high-resolution modelling system is used to simulate wind waves, the water level and the three-dimensional hydrodynamics. The models used are the wave model WAM and the circulation model GETM. The two-way coupling is performed via the OASIS3-MCT coupler. The effects of 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 is significantly enhanced during extreme storm events when considering wave–current interaction processes. This wave-dependent approach yields a contribution of more than 30% in some coastal areas during extreme storm events. The contribution of a fully three-dimensional model compared with a two-dimensional barotropic model showed up to 20% differences in the water level of the coastal areas of the German Bight during Xaver. The improved skill resulting from the new developments justifies further use of the coupled-wave and three-dimensional circulation models in coastal flooding predictions.


Joanna Staneva et al.: Effect of the wave-induced forcing on the North Sea NEMO during extreme storms. EMS Annual Meeting Abstracts Vol. 13, EMS2016-552, 2016


The effects of wind waves on the North Sea hydrography during two storms are investigated using a coupledWAMNEMO model system. The additional terms accounting for wave-current interaction that are considered in this study are the Stokes-Coriolis force, sea-state dependent energy flux and sea-state dependent momentum flux. The individual and collective role of these processes is quantified and the results are compared with observational data that include ADCP observations and continuous measurements from data stations. The analyses of the modelling results and the available observations reveal a closer match with observations for the coupled wave-circulation model, especially during extreme events. The two extreme events, the storm Christian (25-27 of October 2013) and about a month later the storm Xaver (5-7 of December 2013), induce different wave and surge conditions over the North Sea. Including the wave effects in the circulation model for the storm Xaver raises the predicted surge of the coupled model by about 40 cm compared with the standalone ocean model integration for the German Bight area. For the storm Christian, a difference of 20-30 cm in the surge level between the coupled and the standalone ocean model is found over the whole southern part of the North Sea. Moreover, the modeled vertical velocity profile fits the observations very well when the wave forcing is accounted for. The contribution of wave-induced forcing has been quantified and examined indicating that this represents an important mechanism for improving ocean state predictions.

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