The significance of coastal bathymetry representation for modelling the tidal response to mean sea level rise in the German Bight

Abstract

Abstract. Due to climate change an accelerated mean sea level rise is expected. One key question for the development of adaptation measures is how mean sea level rise affects tidal dynamics in shelf seas such as the North Sea. Owing to its flat coastal areas, especially the German Bight (located in the south-east of the North Sea) will be affected. Numerical hydrodynamic models help to understand how mean sea level rise changes tidal dynamics. By definition models cannot represent all processes in overall detail. One limiting factor is the resolution of the model grid. In this study we investigate which role the representation of the coastal bathymetry plays when analysing the response of tidal dynamics to mean sea level rise. Using a shelf model including the whole North Sea and a high-resolution hydrodynamic model of the German Bight we investigate the changes in M2 amplitude due to a mean sea level rise of 0.8 m and 10 m. To the mean sea level rise of 0.8 m the shelf model and the German Bight Model react in different ways. In the shelf model the M2 amplitude generally increases in the region of the German Bight. In contrast, the M2 amplitude in the German Bight Model increases only in some coastal areas and decreases in the northern part of the German Bight. In two case studies we adjust the German Bight Model in order to more closely resemble the shelf model. We find that a different resolution of the bathymetry results in different energy dissipation changes in response to mean sea level rise. Our results show that the resolution of the bathymetry especially in flat intertidal areas plays a crucial role for modelling the impact of mean sea level rise in the order of 1 m. For higher mean sea level rise scenarios (10 m) the resolution of the bathymetry is less important.