Determining the quantitative protection zone of water wells in alluvial unconfined aquifer

Authors

1 Department of Civil Engineering, Dezful Branch, Islamic Azad University, Dezful, Iran

2 Department of Geology, Earth Sciences Faculty, Shahid Chamran University of Ahvaz, Ahvaz, Iran

3 Arizona Department of Water Resources, Phoenix, USA

Abstract

The Quantitative Protection Zone (QnPZ) is an area around the well where water extraction is only allowed through that well. The QnPZ is important, but it does not have proper guidelines. This research explored possible criteria that have not been considered previously. This study was done in an unconfined alluvial aquifer using Modflow and Modpath models. The results showed that drawdown cones (DC) in these aquifers are asymmetric, and as the ratio of discharge (Di) to recharge (Re) increases, the drawdown in the influence zone (IZ) and also the size of the capture zone (CZ) will increase. It was found that the DC of each well will continue to expand until the water table (WT) becomes stable, and the IZ will eventually reach the boundaries of the aquifer. It was found that although the time to reach stability in the DC is long, the time to reach stability in the CZ is shorter. The results showed that both the radius of the IZ and the plan of the CZ cannot be a suitable basis for determining the QnPZ because their extent is very large and variable. It was found that assigning a circular area to each well, so that the volume of a small percentage of Re in that area is equal to the volume of the well Di, can be a suitable basis. However, determining the ratio of Di to Re requires subsidence studies and determining the allowable drawdown of the WT compared to the normal WT.

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Advanced Applied Geology
Volume 15, Issue 1
In progress
March 2025

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