Flow near a pumped well in an unconfined aquifer under nonsteady conditions

Abstract

The problem of unsteady radial flow in an unconfined aquifer is considered as a boundary value problem with discontinuous initial conditions at the surface of the well. The discontinuity of heads occurs at the surface of the well as pumping commences; it dies down in time exponentially and thus represents the delay of the transitional process of reestablishing equilibrium in time. The downward variable movement of water in the vicinity of the well resulting from this discontinuity is proportional to the difference between the gradually falling water table and the average head and is a cause of the slow draining of the unconfined aquifer. The contribution of the unsaturated zone of the aquifer in the process of slow drainage is usually of minor importance and subordinate as far as most drainage problems are concerned. Experimental verification and model design are presented.