Abstract
A procedure is outlined to simulate axisymmetric groundwater flow in radially heterogeneous and layered aquifer systems using the unmodified version of MODFLOW. The procedure is straightforward, as it only requires correction of some of the input parameters. In contrast to other MODFLOW procedures to simulate axisymmetric flow, no restrictions are imposed on the type of flow, the discretization of radial distance, or the parameter values. Hence, the method can deal with both confined and unconfined flow, wellbore storage, and axisymmetric aquifer inhomogeneities including effects of finite-thickness skin and gravel pack. Several test cases are presented, which compare the calculated results with existing analytical solutions, the analytic element solver TTim, and the axisymmetric, finite-difference model MAxSym. It is concluded that the MODFLOW procedure is capable of simulating accurately axisymmetric flow in radially heterogeneous multi-aquifer systems.
Résumé
Une procédure est présentée pour simuler l’écoulement axisymétrique d’eau souterraine dans des systèmes aquifères hétérogènes radialement et stratifiés au moyen de la version non modifiée de MODFLOW. La procédure est simple car elle ne requiert que la correction de quelques paramètres d’entrée. Contrairement à d’autres procédures MODFLOW destinées à simuler un écoulement axisymétrique, aucune restriction n’est imposée au type d’écoulement, à la discrétisation de la distance radiale ou aux valeurs des paramètres. Par conséquent, la méthode peut s’appliquer tant aux écoulements libres que captifs, à l’effet de capacité au puits et aux hétérogénéités de l’aquifère axisymétrique, incluant les effets de skin d’épaisseur finie et du massif de gravier. Plusieurs cas d’étude sont présentés qui comparent les résultats calculés avec des solutions analytiques existantes, le solveur d’éléments analytiques TTim et le modèle aux différences finies axisymétrique MAxSym. Il en est conclu que la procédure MODFLOW est capable de simuler précisément l’écoulement axisymétrique dans des systèmes multi-aquifères radialement hétérogènes.
Resumen
Se describe un procedimiento para simular los flujos de agua subterránea axisimétricos en sistema acuíferos estratificados y radialmente heterogéneos usando la versión no modificada del MODFLOW. El procedimiento es directo ya que solamente requiere la corrección de alguno de los parámetros de entrada. En contraste con otros procedimientos de MODFLOW para simular flujos axisimétricos, no se imponen restricciones en el tipo de flujo, la discretización de las distancias radiales, o los valores de los parámetros. Por lo tanto, que el método puede tratar tanto con flujo no confinado como confinado, almacenamiento en el pozo, e inhomogeneidades axisimétricas del acuífero incluyendo los efectos de películas de espesores finitos y empaque de gravas. Se presentan varios casos de ensayos, que comparan resultados calculados con soluciones analíticas existentes, la resolución del elemento analítico TTim, y el modelo axisimétrico de diferencias finitas MAxSym. Se concluye que el procedimiento de MODFLOW es capaz de simular con exactitud el flujo axisimétrico en sistemas multiacuíferos radialmente heterogéneos.
摘要
本文概述了采用未更改的MODFLOW软件模拟放射状非均匀和层状含水层系统中轴对称地下水流的过程。过程非常简单,因为只需要修改一些输入的参数。与其它MODFLOW模拟轴对称流的过程相比,对水流类型、放射状距离的离散化或参数值没有什么限制。因此,这个方法可以处理承压和非承压水流,钻井孔存储、以及轴对称含水层非均质性包括有限厚度--和砾料的影响。展示了几个实验案例,与用目前的解析方法,解析元TTim方法和轴对称有限差模型MAxSym得到的计算结果进行了对比。结论是MODFLOW的过程能够准确模拟放射状非均匀和层状含水层系统中轴对称流。
Resumo
Descreve-se o procedimento utilizado para simular o escoamento assimétrico de águas subterrâneas em sistemas aquíferos multi-camada radialmente heterogéneos, usando a versão não modificada do MODFLOW. O procedimento é simples, na medida em que apenas requer a correção de alguns dos parâmetros de entrada. Em contraste com outros procedimentos do MODFLOW para simular o escoamento assimétrico de eixos, aqui não é imposta nenhuma restrição nem para o tipo de escoamento, nem para a discretização da distância radial, nem para os valores dos parâmetros. Assim, o método pode lidar com ambas as situações de escoamento confinado e não confinado, armazenamento do poço, e heterogeneidades assimétricas do aquífero, incluindo efeitos de espessura de pele de poço (zona de baixa permeabilidade circundante ao furo) e de filtro de areão calibrado. São testados vários casos que comparam os resultados calculados com soluções analíticas existentes, o elemento analítico da solução TTim, e a simetria axial do modelo de diferenças finitas MAxSym. Conclui-se que o procedimento do MODFLOW é capaz de simular com precisão o escoamento assimétrico em sistemas multi-aquífero radialmente heterogéneos.
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Acknowledgements
Alexander Vandenbohede is supported by the Fund for Scientific Research - Flanders (Belgium) where he is currently a postdoctoral fellow. The authors thank Kick Hemker (author of MLU software) for the fruitful discussions about the infinitely thin skin approach in the last test case. Christian Langevin (USGS) is thanked for verifying the impact of rounding errors on total volumetric budget for the third test case.
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Louwyck, A., Vandenbohede, A., Bakker, M. et al. MODFLOW procedure to simulate axisymmetric flow in radially heterogeneous and layered aquifer systems. Hydrogeol J 22, 1217–1226 (2014). https://doi.org/10.1007/s10040-014-1150-0
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DOI: https://doi.org/10.1007/s10040-014-1150-0