Simulatingflow through multilayer aquifer systems is essential for groundwater management applications such evaluating natural recharge, assessing managed aquifer recharge (MAR), the characterization of surface water–groundwater interactions, and groundwater pollution risk analysis. However, dealing with flow through variably saturated porous media with perched water tables is a difficult task. Usual codes for groundwater flow modeling such as MODFLOW, TOUGH2, and FEFLOW require tedious procedures based on simplified assumptions and approximations. This paper presents a simple approach to simulate two-dimensional flow through perched aquifers and aquitards in deep vadose zones by combining the Dirichlet and Neumann boundary conditions that may apply to any code simulating unsaturated flow. The proposed approach is illustrated with the unsaturated flow code VS2DTI. The main strengths of the proposed methodology are (a) variably saturated flow in the multilayer system is solved using Richards’ equation, taking into account the lateral flow that sustains observed water levels in perched aquifers and variations in recharge; (b) a Dirichlet-type boundary condition at the top perched water table is substituted by a Neumann-type boundary condition, allowing for the representation of any disturbance (e.g., infiltration from ponds, pumping from wells, etc.), regardless of duration and intensity; and (c) the impact of the disturbance is evaluated by comparing the responses of the undisturbed and the disturbed systems. The versatility of this methodology is applied to a MAR case study of a deep aquifer in a sedimentary basin where aquitards limit its feasibility.

中文翻译：

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一种模拟具有二维可变饱和流的多层含水层系统中栖息条件的方法

模拟通过多层含水层系统的流量对于地下水管理应用至关重要，例如评估自然补给、评估管理含水层补给 (MAR)、地表水-地下水相互作用的表征以及地下水污染风险分析。然而，处理流经可变饱和多孔介质和高位水位的流动是一项艰巨的任务。地下水流建模的常用代码（例如 MODFLOW、TOUGH2 和 FEFLOW）需要基于简化假设和近似的繁琐程序。本文提出了一种简单的方法，通过结合 Dirichlet 和 Neumann 边界条件来模拟通过深包水带中的栖息含水层和透水层的二维流动，这些条件可能适用于任何模拟非饱和流动的代码。建议的方法用不饱和流代码 VS2DTI 来说明。所提出的方法的主要优点是 (a) 使用理查兹方程求解多层系统中的可变饱和流，同时考虑到维持栖息含水层中观测到的水位和补给变化的侧向流；(b) 顶部栖息地下水位的 Dirichlet 型边界条件被 Neumann 型边界条件取代，允许表示任何扰动（例如，从池塘渗入，从井中抽水等），无论持续时间如何和强度；(c) 通过比较未受干扰和受干扰系统的响应来评估干扰的影响。