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Well Interference and Drawdown Evaluation Introduction

Under natural (undeveloped) conditions, groundwater levels exist in a dynamic equilibrium where recharge to the aquifer and discharge from an aquifer are approximately equal to each other. Natural recharge processes include recharge from rain, rivers and lakes, and natural discharge processes include discharge to rivers and lakes, and watertable evaporation.

When an aquifer is developed as a water resource, discharge by wells is an additional stress to the aquifer, and the response of the aquifer will depend on the rate of pumping, and hydrogeologic properties of the aquifer. C.V. Theis in 1935 was the first to develop an analytical solution to estimate the response of a confined aquifer to groundwater pumping. Theis's solution assumes that water is drawn from storage by a fully penetrating well, towards which groundwater flows radially from a homogeneous and isotropic aquifer that extends infinitely. Such assumptions are far from reality. Therefore, a number of analytical and numerical solutions had been developed each varying in assumptions and the degree of complexity.

This tool, WIDE, Well Interference and Draw-down Evaluation is developed to demonstrate the response of four major types of aquifers, (1) confined, (2) semi confined with storage, (3) semi confined without storage and (4) unconfined aquifers to groundwater pumping from a single or multiple wells at constant or varying pumping rates. WIDE is based on analytical solutions developed by Theis (1935), Hantush and Jacob (1954), and Neuman (1972), and the principle of super position of solutions. The principle of super position allows the analytical solutions to solve for pumping from several wells, or pumping from a single well at varying discharge rate, or to estimate the rate of recovery, or a combination of any of these.

The intended audiences of this tool are regional hydrogeologists, groundwater users and students in groundwater hydrology. WIDE should be used for demonstration and educational purposes only.

Hantush, M.S. and C.E. Jacob. 1954. Plane potential flow of groundwater with linear leakage. Transactions, American Geophysical Union. 35:917-36.

Neuman, S.P. 1972. Theory of flow in unconfined aquifers considering delayed response of the watertable. Water Resources Research. 9:1031-1045.

Theis, C.V. 1935. The lowering of piezometric surface and the rate of discharge of a well using groundwater storage. Transactions, American Geophysical Union. 16:519-24.