Search

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 low-lying coastal areas, the German Bight (located in the southeast of the North Sea) will be especially affected. Numerical hydrodynamic models help to understand how mean sea level rise changes tidal dynamics. Models cannot adequately 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 and 10 m. The shelf model and the German Bight Model react in different ways. In the simulations with a mean sea level rise of 0.8 m the M2 amplitude in the shelf model 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 the simulations with a mean sea level rise of 10 m the M2 amplitude increases in both models with largely similar spatial patterns. 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.

Within the framework of the current cooperation between the Federal Waterway Engineering and Research Institute (BAW) and the German Aerospace Center (DLR) in the Project TIDE, a possible improvement of the boundary conditions of the hydrodynamic tide model TRIM-2D in the Elbe estuary using satellite data is investigated. The model currently uses a bottom topography boundary condition determined by conventional vessel mounted echo sounder measurements, which is difficult and expensive to update. With the aid of Synthetic Aperture Radar (SAR) data of the European Remote Sensing Satellites (ERS-1/2) it can be shown that this intertidal Elbe estuary region underlies a continual change. This is essential for the model performance and has to be taken into account. The major goal of the TIDE project is the operational extraction of shorelines from the SAR data. The shorelines are transformed to isolines of bottom topography which then can be used as model boundary. The transformation is done either by combining the SAR data with conventional tide gauges or with satellite based ERS-2 altimeter data. To derive topography by satellite is much cheaper and less time consuming than conventional methods, but ifs accuracy has still to be validated against them.