Steady flow to a horizontal drain in an unconfined aquifer with variable thickness
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abstract
In this study, we have used an analytical element method together with genetic algorithm (GA) optimization to determine the steady-state flow rate to an infinite horizontal drain with a finite radius in an unconfined aquifer with a variable thickness. In this study, we first determine the water table position by using the GA optimization method, which is carried out by satisfying the zero pressure and the perpendicularity of iso-potential and iso-pressure gradients on the water table. Then, we illustrate that one has to use a weighting factor in implementing the above-mentioned two conditions simultaneously to optimize the objective function better. Here, we propose two methods to calculate the flow rate to the drain. The first method determines the flow rate based on the water table elevation using the Dupuit-Forchheimer assumption. The second method determines the flow rate by differentiating the hydraulic head. The flow rates calculated by these two methods agree with each other, especially in the regions that are more than 1.8 dimensionless distance from the drain, where the dimensionless distance is defined as the ratio of distance over the drain elevation. The functionality of the flow rate with respect to the drain radius, the drain elevation, and the distance to the constant-head boundary is also studied. 2005 Elsevier B.V. All rights reserved.
