Effects of water table conditions on water level changes near pumping wells

Abstract

Unconfined flow of water to wells is related to anisotropy of the aquifer, changes in the coefficient of storage with time, degree of penetration of the pumping well, and position of the water table. Sluggish response of observation wells to changes of head in the aquifer may lead to erroneous analysis of pumping‐test data. The manner and extent to which these factors affect water levels have been studied by field observation, by analytical equations, and by electric analogs. The typical S‐shaped curves of log drawdown versus log time, observed around wells pumping from water table aquifers, can be explained by an infinity of combinations of possible flow patterns and observation conditions. Equations developed for artesian flow cannot be used for analysis of tests made under water table conditions unless steady‐state conditions have been approached or reached. From a practical standpoint the time required to approach steady flow is much greater than the duration of most pumping tests. Thus if pumping tests are to be used for measuring the hydraulic properties of unconfined aquifers, the boundary conditions attending unconfined flow must be recognized in the analysis of test data.