HGS RESEARCH HIGHLIGHT – Variably saturated dual-permeability flow modeling to assess distributed infiltration and vadose storage dynamics of a karst aquifer
Bresinsky, L., Kordilla, J., Engelhardt, I., Livshitz, Y., & Sauter, M. (2023). 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. In Journal of Hydrology X (Vol. 18, p. 100143). Elsevier BV. https://doi.org/10.1016/j.hydroa.2022.100143
Spatial discretization of the Western Mountain Aquifer and simulation results for 2016-09-15.
A new paper in the Journal of Hydrology provides a perfect case study of the dual continuum formulation supported by HydroGeoSphere. The dual continuum formulation in HydroGeoSphere involves two separate continua, with the first continuum represented by the porous medium. In this case, the 2nd continuum is used to represent the presence of large porosity features (i.e. fractures, conduits and caves) throughout a karstic aquifer.
Water flow through karst aquifers is notoriously difficult to accurately simulate due to these large porosity features which have distinct (and drastically different) flow properties. The dual continuum formulation allows you to represent these features as an overlay (with distinct flow properties) on the porous medium, and the two continua are linked by a fluid exchange term. Estimating infiltration and vadose zone storage (the focus of this research) is yet another layer of complexity, as variably saturated flow (whether based on a single or dual continuum framework) is inherently non-linear.
The paper also includes discussion on the strength of HydroGeoSphere as a tool for predictive hydrologic analysis under changing climate compared to other models, showing that HGS is a suitable tool for modelling “groundwater flow and infiltration dynamics under changing climates with extremes that expand beyond previously experienced conditions. For example, climate change simulations project that average long-term precipitation will decrease, yet the intensity and frequency of short-duration extreme rainfall events will increase.”
“The presented model expands the predictive options compared to previously employed approaches by accounting for fully-distributed (i.e., time and space-dependent) vadose storage dynamics. With the ability to simulate rapid infiltration, the change in storage in the vadose and the phreatic zone, and the characteristics of the karst system dynamics, the constructed flow model has considerable advantages compared to currently available models allowing to predict spatio-temporally distributed recharge and infiltration. ”
Spatial distribution of simulated saturation on 2016-09-15.
CLICK HERE TO READ THE ARTICLE.
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.