Unsteady flow to a pumped well in a fissured aquifer with a free surface level maintained constant

Abstract

New equations are derived for the drawdown in an aquifer consisting of two horizontal layers referred to as the block and the fissure, which have different hydraulic properties. The free water surface forming the upper aquifer boundary is located in the block. The water level is assumed to remain constant during pumping. The block and the fissure are compressible. The depth of the fissure is small in comparison with that of the block. The abstraction well, lined along the block, is pumped at a constant rate. The discharge per unit length of the unlined part in the fissure is constant, and the radius of the well is vanishingly small. Type curves for the drawdown in the fissure and the block are computed and plotted for some selected parameters involved. The effect of the block compressibility on the drawdown in the fissure is shown by comparing the type curves with the type A drawdown curves of Boulton (1963). The influence of the free surface compared with that of an impervious top layer on the drawdown in the fissure and the block is estimated by comparing the type curves with those of Boulton and Streltsova (1977a) found from the equations for a two‐layered formation, the top and bottom surfaces of which are impermeable.