Abstract
In regional scale aquifers in the Rhine Valley and Tabular Jura east of Basel (Switzerland), the groundwater circulation was investigated using regional-scale geological and hydraulic 3D models. The main aquifers in the area comprise the Quaternary aquifer of unconsolidated gravel deposits along the River Rhine and its tributaries, as well as the regional scale karst aquifer within the Upper Muschelkalk. Land subsidence, a process likely associated with salt solution mining, indicates further subordinate groundwater bearing segments and complex groundwater interactions along fault zones. In the aquifer systems we investigated, regional-scale groundwater circulation was simulated and visualized in relation to the geological settings. Lithostratigraphic units and fault structures were parameterized and analyzed, including the sensitivity of hydraulic properties and boundaries. Scenario calculations were used to investigate the sensitivity that the aquifer systems had to hydraulic parameter changes during Quaternary aggradation and degradation in the main valley. Those calculations were also done for base-level changes in the Rivers Rhine and Birs. For this purpose, this study considered probable historic base-levels before river regulation occurred, and before river dams and power plants were constructed. We also focused on scenarios considering increased groundwater recharge rates, e.g. due to exceptional long-lasting precipitation, or heavy rainfall events in the catchment area. Our results indicate that increased groundwater recharge rates in the catchment areas during such events (or periods) are associated with orders of magnitude increases of regional inflow into the Upper Muschelkalk karst aquifer. Furthermore, the groundwater fluctuations and groundwater saturated regions within the karst aquifer shift to places where high densities of sinkholes are documented. When the surface water base-levels adapt to probable historic levels, it leads to increased hydraulic gradients (i.e. local lowering of the groundwater level by up to 7 m). Those increased gradients are associated with increased groundwater flow within some aquifer regions that are particularly prone to karst development.
Highlights
Karst aquifers are characterized by caves, springs, and conduits that form underground drainage systems, which were shaped by dissolution, whereas subsidence processes can lead to sinkholes (Ghasemizadeh et al 2012)
The concept of the steady-state regional-scale numerical 3D hydraulic model is based on the approach of Tóth (2009), which assumes the topography acts as the hydraulic “engine” for the underlying regional groundwater circulation
A reduction of the hydraulic conductivity leads to lower groundwater heads in the Upper Muschelkalk” (UMK) aquifer for most observation wells (OW), which can be explained by the reduced exchange between the unconsolidated gravel and the UMK aquifer
Summary
Karst aquifers are characterized by caves, springs, and conduits that form underground drainage systems, which were shaped by dissolution (subrosion), whereas subsidence processes can lead to sinkholes (Ghasemizadeh et al 2012). Since sinkholes develop from subsidence, they have been. Many areas in Central Europe are characterized by complex landforms and geological settings that produce multiscale groundwater flow systems (Tóth 1963b). Environmental Earth Sciences (2021) 80:201 important ones is the energy provided from hydrostatic head differences, which causes groundwater flow through the system (Anderson and Kirkland 1980; Cooper 2002; Johnson 1981, 2005). Gravity drives groundwater flow in a sedimentary basin, and it is thought to be a superposition of several flow systems. Topography and anisotropy determine the geometry and the penetration of different flow systems (Tóth 1962, 1963a, 1995). That concept was later extended by Zijl (1999) as well as by Butscher and Huggenberger (2007), Marklund and Worman (2011), Tóth (2009) and Worman et al (2007)
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