Modeling Ground Water Flow in Alluvial Mountainous Catchments on a Watershed Scale

Abstract

In large mountainous catchments, shallow unconfined alluvial aquifers play an important role in conveying subsurface runoff to the foreland. Their relatively small extent poses a serious problem for ground water flow models on the river basin scale. River basin scale models describing the entire water cycle are necessary in integrated water resources management and to study the impact of global climate change on ground water resources. Integrated regional-scale models must use a coarse, fixed discretization to keep computational demands low and to facilitate model coupling. This can lead to discrepancies between model discretization and the geometrical properties of natural systems. Here, an approach to overcome this discrepancy is discussed using the example of the German-Austrian Upper Danube catchment, where a coarse ground water flow model was developed using MODFLOW. The method developed uses a modified concept from a hydrological catchment drainage analysis in order to adapt the aquifer geometry such that it respects the numerical requirements of the chosen discretization, that is, the width and the thickness of cells as well as gradients and connectivity of the catchment. In order to show the efficiency of the developed method, it was tested and compared to a finely discretized ground water model of the Ammer subcatchment. The results of the analysis prove the applicability of the new approach and contribute to the idea of using physically based ground water models in large catchments.

Groundwater and Surface Water Interaction at the Regional-scale – A Review with Focus on Regional Integrated Models

“…These efforts ran into a multitude of problems which had not been described or solved previously (see, e.g. Götzinger et al 2008;Wolf et al 2008). Attempts to apply concepts that are well-established at smaller scales were not successful.…”

“…Some of these difficulties have been discussed in detail in previous publications (Barthel 2006;Barthel et al 2008a;Götzinger et al 2008;Rojanschi et al 2006;Wolf et al 2008). For example, huge problems arise when groundwater recharge, calculated by conceptual hydrological models is applied to physics-based numerical groundwater flow models because the spatial distribution of this recharge does not take into account the geology of regional aquifers (discussion in Barthel 2006;Jie et al 2011;Wolf et al 2008). But most importantly, it became evident that data availability is far from sufficient, e.g.…”

“…Our own experiences from the GLOWA-Danube project for the Upper Danube catchment (77,000 km², Barthel et al 2012;Ludwig et al 2003) and in the RiverTwin project for the Neckar catchment (14,000 km², Barthel et al 2008a;Gaiser et al 2008) in Germany gave deeper insights of the tremendous challenges associated with integrated modelling at the regional scale. Some of these difficulties have been discussed in detail in previous publications (Barthel 2006;Barthel et al 2008a;Götzinger et al 2008;Rojanschi et al 2006;Wolf et al 2008). For example, huge problems arise when groundwater recharge, calculated by conceptual hydrological models is applied to physics-based numerical groundwater flow models because the spatial distribution of this recharge does not take into account the geology of regional aquifers (discussion in Barthel 2006;Jie et al 2011;Wolf et al 2008).…”

“…Another issue is that river bottom elevations above a common datum (sea level) are quite often not available for all potentially relevant river reaches. Hence, channel bottom elevations have to be fitted or derived from proxy data (Scibek et al 2007;Wolf et al 2008). This leads to a general problem within loosely coupled systems: GW-SW in such systems has to be based on the calculation of the exchange fluxes as a result of potential differences, the geometry of the river bed, and its hydraulic properties.…”

Global Warming Induced Water-Cycle Changes and Industrial Production - A Scenario Analysis for the Upper Danube River Basin

“…Ground water balance This sub-project group implemented models to simulate ground water flow and ground water quality (Barthel et al 2005a, Barthel et al 2005b, Wolf et al 2008 as well as the water supply for the upper Danube catchment area.…”