NHESS Natural Hazards and Earth System Sciences NHESS Nat. Hazards Earth Syst. Sci. 1684-9981 Copernicus Publications Göttingen, Germany 10.5194/nhess-9-1277-2009 Coupled modelling of subsurface water flux for an integrated flood risk management Sommer T. 1 Karpf C. 2 Ettrich N. 3 Haase D. 4 Weichel T. 4 7 Peetz J.-V. 5 Steckel B. 5 Eulitz K. 1 8 Ullrich K. 6 Dresden Groundwater Research Centre, Meraner Straße 10, 01187 Dresden, Germany TU Dresden, Institute for Urban Water Management, 01062 Dresden, Germany Fraunhofer Institut für Techno- und Wirtschaftsmathematik (ITWM), Fraunhoferplatz, 67663 Kaiserslautern, Germany Helmholtz Centre for Environmental Research – UFZ, Permoserstraße 15, 04318 Leipzig, Germany Fraunhofer Institute for Algorithms and Scientific Computing (SCAI), Schloss Birlinghoven, 53754 Sankt Augustin, Germany Environmental Office of Capital Dresden, Grunaer Straße 2, 01069 Dresden, Germay now at: Landesbetrieb für Hochwasserschutz und Wasserwirtschaft, Magdeburg, Germany now at: Ingenieurbüro für Grundwasser, Leipzig, Germany 29 07 2009 9 4 1277 1290 Copyright: © 2009 T. Sommer et al. 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://nhess.copernicus.org/articles/9/1277/2009/nhess-9-1277-2009.html The full text article is available as a PDF file from https://nhess.copernicus.org/articles/9/1277/2009/nhess-9-1277-2009.pdf

Flood events cause significant damage not only on the surface but also underground. Infiltration of surface water into soil, flooding through the urban sewer system and, in consequence, rising groundwater are the main causes of subsurface damage. The modelling of flooding events is an important part of flood risk assessment. The processes of subsurface discharge of infiltrated water necessitate coupled modelling tools of both, surface and subsurface water fluxes. Therefore, codes for surface flooding, for discharge in the sewerage system and for groundwater flow were coupled with each other. A coupling software was used to amalgamate the individual programs in terms of mapping between the different model geometries, time synchronization and data exchange. The coupling of the models was realized on <i>two</i> scales in the Saxon capital of Dresden (Germany). As a result of the coupled modelling it could be shown that surface flooding dominates processes of any flood event. Compared to flood simulations without coupled modelling no substantial changes of the surface inundation area could be determined. Regarding sewerage, the comparison between the influx of groundwater into sewerage and the loading due to infiltration by flood water showed infiltration of surface flood water to be the main reason for sewerage overloading. Concurrent rainfalls can intensify the problem. The infiltration of the sewerage system by rising groundwater contributes only marginally to the loading of the sewerage and the distribution of water by sewerage has only local impacts on groundwater rise. However, the localization of risk areas due to rising groundwater requires the consideration of all components of the subsurface water fluxes. The coupled modelling has shown that high groundwater levels are the result of a multi-causal process that occurs before and during the flood event.

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