A numerical study of confined‐unconfined aquifers including effects of delayed yield and leakage

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Abstract
This report presents a numerical model in radial coordinates for a well penetrating a homogeneous isotropic aquifer of constant thickness. The model defines variations in the transmissivity and effective storage coefficient as functions of the potential. This allows an approximation for the problem of a well pumping in an initially confined system which becomes unconfined near the well as the potential surface drops below the confining layer of the aquifer (confined‐unconfined problem). The model is used to investigate effects of delayed yield and leakage in confined‐unconfined aquifers. Drawdown versus time curves are presented for a variety of boundary conditions. Results show that the conditions producing an inflection in the drawdown versus time curves are not unique and illustrate the difficulty in attempting to determine aquifer characteristics from pumping test data.