Nonsteady-State Drawdowns in Two Coupled Aquifers

Abstract

A nonsteady coupled aquifer solution is developed in which transient and steady-state drawdowns can be calculated in a pumped aquifer and in an overlying unpumped aquifer that is separated from the pumped aquifer by a semipermeable confining bed. The water pumped is from artesian storage in the pumped aquifer and leakage through the overlying confining bed. This leakage is from storage in the water-table aquifer and a reduction in evapotranspiration due to a decline in the water table. As a simplifying assumption, storage in the confining bed is neglected. This solution is different from existing analytical solutions in that steady-state conditions can be reached because a source term representing the evapotranspiration reduction is included in the differential equations that are solved. A Laplace-space solution obtained for the differential equations and boundary conditions is inverted to the time domain using the Stehfest numerical algorithm. The resulting time-dependent solution is an efficient tool for making preliminary estimates and identifying additional data needs. Also, it can be used to verify solutions obtained using more complex analytical and numerical models.