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Amin Ahmadi, Gholamreza Mirzavand, Maryam Zebarjad,
Volume 17, Issue 3 (12-2023)
Abstract

The zone of influence of the well is the area where the activity of the well changes the water level. The zone of influence is important in determining the protection zones; however, in this regard, reliable relationships have not yet been presented and their lack of relationship has not been confirmed; and this is due to the lack of accurate knowledge of the zone of influence in some aquifers. This study was carried out using the MODFLOW model to know the effect of aquifer physical parameters on the drawdown cone in an unconfined alluvial aquifer with a sloping water surface; and since no such research has been reported so far, the results are innovative. The results showed that although it is possible to ignore the effect of a well in parts of the aquifer due to measurement and presentation limitations, in practice the influence zone of each well will extend to the outer physical boundaries. It was found that two types of real and theoretical drawdown cones can be discussed in the influence zone and each should be analyzed separately. It was found that parameters such as hydraulic conductivity, saturation thickness, transmissivity, horizontal anisotropy, bed slope, and amount of recharge in sloping unconfined aquifers have a dual effect on the drawdown cone, and if their high values decrease the drawdown in short distances, they increase the drawdown in long distances. It was found that normal heterogeneity does not change much on the drawdown cone, and the reason is the opposite effects of hydraulic conductivity and specific yield on the drawdown value. It was found that hydraulic conductivity, horizontal anisotropy and specific yield have a strong effect, but vertical anisotropy and heterogeneity have a negligible effect on the drawdown cone.

Amin Ahmadi, Maryam Zebarjad, Ghoramreza Mirzavand,
Volume 18, Issue 1 (5-2024)
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.


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