| Abstract: | Flow simulation in rivers is used for the prediction of waterlevel and runoff quantities. The presently used simulation by the German Federal Institute of Hydrology is based on a network approach with coupled 1d models in which the river flow is described by the St. Venant‐equations. Work is underway to extend this by 2d submodel elements using the shallow water equations to allow simulations in greater detail. The wetting and drying of parts of the river bed at varying waterlevels force us to formulate the flow simulation as free boundary problem. The constraints of embedding the 2d model into the existing network approach suggest to use a fixed grid approach. This leads to the problem of solving the shallow water equations on the whole grid. However, the shallow water equations degenerate for dry beds and therefore do not allow a straight forward discretisation. |
