Coupled modelling of subsurface water flux for an integrated flood risk management

Abstract

Abstract. 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 two 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 groundCorrespondence to: T. Sommer (tsommer@dgfz.de) water 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.

Groundwater flooding in a river‐connected alluvial aquifer

“…Here we distinguish groundwater flooding via connections to wastewater collection infrastructure from sewer backup, and define the former as shallow groundwater that enters a home via holes or cracks in the wastewater collection system under elevated groundwater pressure, and not by blockage in the wastewater collection system. Complex relationships between groundwater infiltration, surface water inflow, and sewage exfiltration during a flood have been modeled, indicating river stage fluctuations can lead to groundwater flooding, and ultimately overload sewage systems (Cloutier et al, ; Karpf et al, ; Sommer et al, ).…”

Analysis and integrated modelling of groundwater infiltration to sewer networks

“…() who use mouse–mike she coupling and Sommer et al . () who apply trimr2d (Washington Water Science Center, U.S. Geological Survey, Tacoma, Washington) (groundwater) and hystem‐extran (itwh GmbH, Hannover, Germany) (sewer system). Berggren et al .…”

Groundwater infiltration, surface water inflow and sewerage exfiltration considering hydrodynamic conditions in sewer systems

“…As rainfall event a virtual rain with a duration of 12 h and a frequency of 1 a -1 and a rain height of 36 mm is generated as a rectangle-shaped rainfall according to rain statistics in the Dresden catchment. Groundwater levels are taken from a groundwater simulation of a 100-year flood event, which was realised with a hydrodynamic 3D model (Sommer et al 2009). Surface water levels are generated by a linear interpolation of the river water level during a 100-year flood event.…”

“…The integrated coupling of hydrodynamic sewer, surface-and groundwater models was realised e.g. by Sommer et al (2009), who coupled a sewer network model (1D) with a surface water model (2D) and a groundwater model (3D). Besides the complexity of the model coupling, the collection of the data needed and its processing, the set-up of the model structure and definition of boundary conditions are very labour-intensive.…”