Hydrochemical changes induced by overexploitation of groundwater at common outlets of the Bet Shean-Harod multiple-aquifer system, Israel

Abstract

The Bet Shean and Harod Valleys are regional recipients and mixing zones for groundwaters draining into them from a multiple-aquifer system which includes carbonate and basalt aquifers and deep-seated reservoirs of brine. The aquifers drain through two types of outlets — unique and common. The latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers. Ca-chloride brines originating from deep-seated and confined reservoirs, leak along the major faults and contaminate the relatively fresh groundwaters originating from the regional aquifers. During the last two decades, the salinity of groundwaters at the outlets of aquifers and in springs discharging into the valleys, have increased as the result of overexploitation. The changes in the chemical composition of these waters indicated inflow of dilute Ca-chloride brines which replace at an ever increasing rate the fresh water of the area. The inflow of brines is limited to fault zones and seems to be controlled by the counterpressure of the overlying fresh water. Overexploitation diminishes this counterpressure, thus facilitating the progressive upflow of brines.