Variably saturated dual-permeability flow modeling to assess distributed infiltration and vadose storage dynamics of a karst aquifer – The Western Mountain Aquifer in Israel and the West Bank

Abstract

Available methods to quantify the recharge of karst aquifers usually rely on spatially and temporally aggregated precipitation measurements and simplified recharge models, employing transfer functions to account for the delay in infiltration and the distribution in time and space. They generally neglect the non-linear nature of infiltration dynamics through the vadose zone, characterized by dual flow behavior with slow diffuse and rapid focused recharge components. Here, we present a methodology that accounts for the physics of flow by employing a variably saturated dual-permeability flow model to simulate diffuse and preferential infiltration in a large-scale carbonate aquifer. The Western Mountain Aquifer (WMA) in Israel and the West Bank was selected as a suitable groundwater basin because of the large thickness of the vadose zone, extending over several hundred-meters, the availability of long-term data as well as the catchment size, stretching across a catchment area of circa 9000km². Together, these characteristics allow the identification and quantification of the spatio-temporal distribution of the infiltration/recharge component, assessed at the level of the groundwater table. The presented methodology allows for improved water resources planning and generalization of the results, i.e., the robustness of large-scale model results with respect to local hydraulic parameter variations and data uncertainty. Semi-arid climate regions with a highly pronounced seasonality of precipitation and intense short-duration rainfalls, such as the Mediterranean region, represent a prime study location because of the clear and pronounced recharge input signals that are not superimposed by summer rainstorms. We simulate the complex dynamics of the dual-domain infiltration and partitioning of the precipitation input signal by employing HydroGeoSphere (HGS) for transient variably saturated water flow. Flow in the limestone rock matrix and high porosity system (i.e., conduits and fractures) is modeled by overlapping individual continua based on the bulk-effective Richards’ equation with van Genuchten (VG) parameters.