Drawdowns in Coupled Aquifers with Confining Unit Storage and ET Reduction

Abstract

AbstractThis paper presents a nonsteady coupled aquifer solution in which transient and steady‐state drawdowns due to pumping can be calculated in one or both of two aquifers separated by a semipermeable confining unit in a confined aquifer system. The water pumped is obtained from storage in the aquifers and the confining unit, and a reduction in evapotranspiration (ET) due to a decline in the water table. This solution is different from existing analytical solutions in that it includes both confining unit storage and a drawdown‐dependent ET reduction term. A Laplace space solution obtained for the differential equations subject to the initial and boundary conditions is inverted to the time domain using the Stehfest numerical algorithm. The presence of the ET reduction term in the solution allows the drawdowns to reach a steady‐state condition, and the presence of the confining unit storage term delays the response of the aquifer system to pumping, particularly in the unpumped aquifer. Use of the solution to calculate drawdowns for a representative field case is illustrated, along with verification of the solution using a numerical ground water flow model.