Karstification beneath the Birs weir in Basel/Switzerland: A 3D modeling approach

SummaryWe present a three-dimensional model describing the evolution of a gypsum karst aquifer along the Birs river near Basel in Switzerland. Here, a small dam-site was built in 1890 to generate hydro-electric power. After subsidence of a nearby highway, geophysical and geological field studies have been carried out and a detailed hydrogeological model has been developed. These observations identified a karstified weathered zone as the reason for the subsidence. To prevent any further damage, remedial construction measures have been carried out. We employ our numerical model KARSTAQUIFER, which simulates the temporal evolution of a karst system by dissolution, increasing the porosity in the aquifer. We used results from geological and geophysical investigations as a priori information for implementing the initial boundary conditions into our three-dimensional numerical model. Our model accounts for topography, precipitation and geology and especially for the anisotropy of the local bedrock. It can successfully reproduce the weathered zone in its current horizontal and vertical extent. We can also simulate the possible evolution of the aquifer following a remedial construction phase. Therefore, taken together with the geophysical and geological observations and the groundwater model, our three-dimensional karst aquifer evolution model enhances the understanding of the development of this heterogeneous karst aquifer system.

► Three-dimensional karst evolution modeling of a gypsum karst aquifer.
► Influence of a dam-site on the creation of a karstified weathered zone.
► Geological and hydrogelogical information set the boundary conditions for our model.
► Showing the effect of anisotropy and topography on the evolution of the model.
► The final model successfully reproduces the weathered zone in its current extent.