Quantification of groundwater recharge from an ephemeral stream into a mountainous karst aquifer

Sustainable groundwater production from karst aquifers is primarily dictated by its recharge rate. Therefore, it is essential to accurately quantify annual groundwater recharge in order to limit overexploitation and to evaluate artificial methods for groundwater enrichment. Infiltration during erratic flood events in karst basins may substantially contribute to aquifer recharge. However, the complicated nature of karst systems, which are characterized in part by multiple springs, sinkholes, and losing/gaining streams, impede accurate quantification of the actual contribution of flood waters to groundwater recharge. In this study, we aim to quantify the proportion of groundwater recharge accrued during runoff events in a karst aquifer. The role of karst conduits on flash flood infiltration was examined during four flood and controlled runoff events in the Soreq creek near Jerusalem, Israel. We distinguished between direct infiltration, percolation through karst conduits, and diffuse infiltration-the latter of which is most affected by evapotranspiration. A water balance was calculated for the 2014/15 hydrological year using the Hydrologic Engineering Center-Hydrologic Modelling System (HEC-HMS). Simulations show that 6.8 to 19.2% of the annual recharge volume was added to the aquifer from infiltration of runoff losses along the creek through the karst system.