Integrated urban flash flood modelling in hillside catchments

Stefan Leitner, Gerald Krebs and Dirk Muschalla


Central Europe sees an increase of urban flash floods due to local heavy storm events. Urbanization and the global climate change are key drivers for this trend. Flood models are a helpful tool to understand the dynamics of urban flash flood events. 1D-2D hydrodynamic models for pluvial floods (1D for the sewer model and 2D for surface flow in the case of surcharching) and 2D hydrodynamic stream models for fluvial floods currently define the state of the art. In the context of urban flash flood events, the hillside substantially affects the surface-runoff generation, especially in Austria, due to the mountainous topography. For this reason, the interactions between i) hillside - urban streams and ii) hillside - urban area (including the sewer system) must be taken into account with respect to surface-runoff generation. These relationships require an integrated modelling approach comprising three sub-systems (hillside, urban streams and urban area) and their interactions as well as hydrological and hydraulic models in a multiple unidirectional and bidirectional way. The result is an integrated surface model with the opportunity to calculate the surface water depth and flow velocity. Such models are a good basis for further analysis, for example an urban flash flood risk assessment.

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