Effects of fault systems on unsaturated and saturated flow dynamics in karst aquifers

Marcus Veltri1, Alexa Terrell1, Jannes Kordilla1, Sebastian Schmidt1, Martin Sauter1
1 University of Göttingen, Geosciences Centre

P 8.7 in Karstgrundwasserleiter – Neue Entwicklungen und Methoden in Charakterisierung und Modellierung dualer Fließsysteme

Fault zones provide rapid groundwater flow paths in many aquifer systems and are considered of importance in recharge dynamics. Here we numerically study saturated and unsaturated flow in karstified aquifer systems situated in two field sites, draining to the Leine Valley, Göttingen, Germany. The sites are similar with respect to the general aquifer geology, climatic conditions as well as regional groundwater flow conditions but different with respect to the degree of faulting. These are the Weendespring and Gronespring catchments, located on opposite sides of the Leinetalgraben in Göttingen, Germany, and intersected by seven and one fault zone(s), respectively. The vulnerability of the aquifers within these catchments with respect to groundwater contamination is of interest due to their importance as a drinking water supply resource. The catchments are conceptualized with three distinct hydrogeological limestone/marl units of the Triassic Muschelkalk. The Upper and Lower Muschelkalk units are highly conductive and separated by a middle aquitard unit intersected by fault zones. Using the finite element COMSOL Multiphysics® modeling software, infiltration through the unsaturated zone is considered using the Richard’s equation with a van Genuchten type parameterization. Fault zones are implemented as highly conductive zones with thicknesses derived from field measurements. The impact of the fault zone density on regional catchment flow dynamics is studied by an inverse modeling approach, considering different patterns of spring discharge. Comparisons are drawn between the two catchments based upon their fault zone contributions to (a) preferential groundwater flow, (b) recharge infiltration across the vadose zone and (c) the cumulative effect on the overall karst flow dynamics.