6-Unsteady flow to a well in multiple confined aquifers.

Abstract

Transient ground water flow to a fully penetrating well installed in n-confined aquifers (n is an integer) separated by aquicludes has been analysed. The aquifers were in hydraulic equilibrium before the start of pumping. Explicit equations for drawdown distribution in each aquifer as well as its contribution to the well discharge have been developed. The solution for drawdown distribution in each aquifer is simple like Theis equation in which aquifer transmissivity is replaced by an effective transient transmissivity of the aquifer. When the diffusivities of the aquifers are equal, the solution reduces to Theis equation. The solution is approximate and is valid for large times such that the variable r2 Si/4Tit < 0.05. The analysis has revealed that (i) the contribiuton of an aquifer to the well discharge during transient state is governed by the aquifer diffusivity, (ii) at the start of pumping the ground water flow to the well is more from an aquifer of the least aquifer diffusivity, and (iii) the flow from aquifers of equal diffusivities is invariant over time and is proportional to aquifer transmissivities with proportionality constant being equal to the inverse of the sum of the aquifer tranamissivities. The difference in drawdowns between two radial distances in each aquifer follow a Thiem type equation.