Groundwater Hydrology

Poster Abstract

Comparison of Preconditioned Conjugate Gradient Method and Strongly Implicit Procedure in Modflow

Wednesday, January 4
10:00 AM - 5:00 PM
Location: ChuLv Hall

The modular finite-difference flow model is called MODFLOW developed by US. Geological Survey, which is a powerful computer program used to simulate groundwater flow. In numerical modeling of groundwater flow, solving a large sparse system of linear equations can be a problem for convergence and accuracy for some applications. In particular, prediction of land subsidence using MOFLOW requires higher accuracy than other applications. Therefore, solution’s convergence and accuracy play an important role in modeling land movement that may be caused by ground fluid withdrawal. This study is to evaluate the convergence and accuracy of two most popular iterative methods, Strongly Implicit Procedure (SIP) and Modified Incomplete Cholesky Conjugate Gradient (MICCG). Both the SIP and MICCG methods were utilized as the solvers in MODFLOW for 2D and 3D groundwater flow models. The considered conceptual model is an aquifer system having an aquitard sandwiched by an overlying unconfined aquifer and an underlying confined aquifer, respectively. A pumping well was installed into the confined aquifer. The complete mathematical description for regional flow includes the flow equation along with the initial and boundary conditions. Several simulations were performed with a constant pumping rate using the two different solvers.  The data from SIP and MICCG were compared not only with each other but also with analytic solutions. The results using the MICCG algorithm in both 2D and 3D groundwater flow showed faster convergence and higher accuracy than those using the SIP approach. However, if the optimum values for its parameters were carefully selected, the SIP solver can also generate convergent and accurate solutions for the 2D model but, not for 3D. 

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Comparison of Preconditioned Conjugate Gradient Method and Strongly Implicit Procedure in Modflow



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