Time response of the water table and saltwater transition zone to a base level drop

This paper investigates the effect of a drainage base level drop on the groundwater system in its vicinity, using theoretical analysis, simulations, and field data. We present a simple and novel method for analyzing the effect of a base level drop by defining two characteristic times that describe the response of the water table and the transition zone between the fresh and saline water. The Dead Sea was chosen as a case study for this process because of the lake's rapid level drop rate. During a continuous lake level drop, the discharge attains a constant value and the hydraulic gradient remains constant. We describe this new dynamic equilibrium and support it by theoretical analysis, simulation, and field data. Using theoretical analysis and sensitivity tests, we demonstrate how different hydrological parameters control the response rate of the transition zone to the base level drop. In some cases, the response of the transition zone may be very rapid and in equilibrium with the water table or, alternatively, it can be much slower than the water table response, as is the case in the study area.