Abstract

The Upper Cretaceous Judea carbonate-rock aquifer is situated between the base levels of the Mediterranean Sea in the west and the Jordan rift valley in the east, which have a maximum elevation difference of 400 m. The gradients of the ground-water table vary from very steep (8%) to very moderate (0.04%). The present ground-water divide in the uplifted central Israeli mountains coincides with the north-south structural axis. The divide in the Yizre'el and Beer Sheva morphotectonic valleys, which cut across these mountains, is located very close to the Mediterranean base level. These valleys have a past history of repeated penetration by the sea since Neogene time. In Pliocene time the Mediterranean and the Jordan rift valley had the same elevation. Thus, one would expect that the divide was situated half way between them. It can be shown, theoretically, that the later subsidence of the rift valley relative to the Mediterranean should have caused a westward shift and a simultaneous lowering of the ground-water divide, as the eastern gradients became more gentle. This is the case in the Yizre'el and Beer Sheva valleys, where the bottom of the aquifer is below the base levels and the location of the ground-water divide is not controlled by the underlying structure. Although structural control appears to be dominant in the study area, it is recognized that the location of the divide is also controlled by nonuniformity of recharge and hydraulic conductivities. Some of the present water tables have a past history as parts of the paleo–ground-water systems. These are identified on the basis of fossil karst systems and gentle gradients leading to ancient base levels, indicated by nearshore marine or lacustrine sediments.

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