The effect of hydrogeological conditions on variability and dynamic of groundwater recharge in a carbonate aquifer at local scale Noam Zach Dvory a,b,⇑ , Yakov Livshitz c , Michael Kuznetsov a , Eilon Adar a , Alexander Yakirevich a a Zuckerberg Institute for Water Research, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Israel b Etgar A. Engineering Ltd., Israel c Israel Hydrological Service, Israel Water Authority, Israel article info Article history: Received 29 September 2015 Received in revised form 27 December 2015 Accepted 9 February 2016 Available online 15 February 2016 This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of Hund-Der Yeh, Associate Editor Keywords: Karst aquifer Dual porosity model Vadose zone Spatial recharge variation summary Groundwater recharge in fractured karstic aquifers is particularly difficult to quantify due to the rock mass’s heterogeneity and complexity that include preferential flow paths along karst conduits. The pre- sent study’s major goals were to assess how the changes in lithology, as well as the fractured karst sys- tems, influence the flow mechanism in the unsaturated zone, and to define the spatial variation of the groundwater recharge at local scale. The study area is located within the fractured carbonate Western Mountain aquifer (Yarkon-Taninim), west of the city of Jerusalem at the Ein Karem (EK) production well field. Field monitoring included groundwater level observations in nine locations in the study area during years 1990–2014. The measured groundwater level series were analyzed with the aid of one- dimensional, dual permeability numerical model of water flow in variably saturated fractured-porous media, which was calibrated and used to estimate groundwater recharge at nine locations. The recharge values exhibit significant spatial and temporal variation with mean and standard deviation values of 216 and 113 mm/year, respectively. Based on simulations, relationships were established between precipita- tion and groundwater recharge in each of the nine studied sites and compared with similar ones obtained in earlier regional studies. Simulations show that fast and slow flow paths conditions also influence annual cumulative groundwater recharge dynamic. In areas where fast flow paths exist, most of the groundwater recharge occurs during the rainy season (60–80% from the total recharge for the tested years), while in locations with slow flow path conditions the recharge rate stays relatively constant with a close to linear pattern and continues during summer. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Unsaturated flow mechanisms and groundwater recharge in fractured carbonate aquifers are highly influenced by rock mass diversity. The deposition processes of sedimentary bodies vary in time and location (Wright and Burchette, 1996). These processes are the basis for facial distributions in the rock mass which is later affected by various physical and chemical processes. Water flow through the rock mass, both in the vadose and the saturated zones, is influenced by the media hydraulic properties’ spatial deviations (Montazer and Wilson, 1984; Flint et al., 2001a; Hartmann et al., 2014; Mahmud et al., 2015). Low permeability layers that are located in the vadose zone and act as impermeable or partly imper- meable flow boundaries within the aquifer are a basis for different scales perched water bodies in the unsaturated zone (Flint et al., 2001b; Kordilla et al., 2012; Heaton et al., 2012; Allocca et al., 2015). Heterogeneity of rock properties affects spatial and tempo- ral distribution of recharge and subsurface flow dynamics during varying hydroclimatic conditions (Hartmann et al., 2015). The hydrogeological section in Fig. 1 illustrates the major path- ways of water flow in the unsaturated zone flow of karst aquifers. Within this section, two flow paths’ end members can be observed. In the first (A), fast flow occurs from surface sources, such as pre- cipitation and runoff, by karst and fault conduits in the unsaturated zone. The second end member (B) marks slow flow conditions in which the flow path passes through matrix and unkarstified fis- sures and encounters low permeability layers that delay the flow front. The described conditions are common in the thick phreatic parts of sedimentary aquifers and present bigger challenges in fractured carbonate aquifers where preferential flow occurs. In such sections, significant rapid groundwater-level fluctuations that are related to the first end member can occur. Examples of large http://dx.doi.org/10.1016/j.jhydrol.2016.02.011 0022-1694/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Hermon 27, Rosh Haayin 4857137, Israel. Tel.: +972 54 2330223. E-mail address: nzd@etgar-eng.com (N.Z. Dvory). Journal of Hydrology 535 (2016) 480–494 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol