Engineering Geology

Engineering Geology

Influence of well physical parameters on the cone of depression in the zone of influence of water wells in unconfined alluvial aquifers

Authors
Amin Ahmadi 1
Maryam Zebarjad 2
Ghoramreza Mirzavand 1
1 Department of Civil Engineering, Dezful Branch, Islamic Azad University, Dezful, Iran
2 Department of physics, Dezful Branch, Islamic Azad University, Dezful, Iran
10.22034/JEG.2024.18.1.1019243
Abstract
The zone of influence is the area where water withdrawal from the well causes the water level to fall. The drawdown cone is a conical shape of the water level in the zone of influence, and it is necessary to know the effect of the factors influencing it. Previous studies have mainly investigated aquifers with horizontal water levels and less realistic conditions. The purpose of this study is to investigate the effect of well physical parameters on the drawdown cone in one of the unconfined aquifers with a sloping water surface. In this aquifer, a normal discharge well was simulated using the Modflow program and the effect of the target parameters was studied. The results showed that: the drawdown cone is symmetrical up to long pumping and relatively long distances; the zone of influence will eventually extend to the entire aquifer and significant drawdown will occur at long distances. A significant part of the drawdown in the well is recovered in the first moments of pump shutdown, but at long distances, the drawdown continues to increase for a long time. An inflection point can be extracted from the drawdown cone which represents the minimum drawdown that does not increase after the pump is stopped and can be introduced as a unique value. By increasing the flow several times, the depth of the cone increases, but the width of the cone increases only slightly. If the pump is turned on and off successively, the general shape of the cone does not depend on the nominal discharge of the well, but mainly on the average discharge of the aquifer. Relative infiltration increases the depth of the cone only near the well and has no significant effect on its shape further away.
Keywords
Drawdown cone
groundwater
Influence Zone
Radius Influence
Water wells
MODFLOW
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