Evaluation of Rapid Recharge Processes and Spring Source Vulnerability of Karst Aquifers in Semi-arid Environments

Abstract:

Due to focussed recharge mechanisms and rapid conduit flow, karst aquifers are often very vulnerable to anthropogenic contamination, especially concerning water abstraction from karst springs. This groundwater source vulnerability is highly variable in time, depending on the temporal variability of precipitation and recharge conditions. The critical fast flow component can be assessed by high-resolution monitoring of spring hydrographs and chemographs and their combined analysis. However, because of the lack of data this has been rarely conducted for karst aquifers in arid or semi-arid climate regions, despite the episodic nature of recharge and associated low signal convolution in those environments. A continuous monitoring scheme was implemented at four major karst springs located in the Lower Jordan Valley near Jericho together with meteorological stations and monitoring wells in the recharge area. The results enable (1) the quantification of the fast flow component and associated source vulnerability parameters at the springs, (2) insights into the hydrogeological characteristics of the flow system, e.g. karst network geometry and conduit system volumes, and (3) the evaluation of rapid recharge processes, i.e. the relative importance of flow concentration in the epikarst and rapid vadose zone percolation vs. the infiltration of episodic surface runoff into ponors. Furthermore, the seasonal variable wastewater impact at the springs and hence the epikarst–vadose zone–matrix–conduit interaction can be qualitatively evaluated.