Evaluation of Local Grid Refinement Methods for Block-Centered Finite-Difference Groundwater Models

A new method of local grid refinement for two-dimensional block-centered finite-difference meshes was developed. The method uses an iteration-based feedback to couple two separate grids. The new method was evaluated by comparison with results using a uniform fine mesh, a variably spaced mesh, and a traditional method of local grid refinement without a feedback. Results indicate that (1) the new method exhibits quadratic convergence for homogeneous systems and convergence equivalent to uniform grid refinement for heterogeneous systems, (2) rigorously coupling the coarse grid with the refined grid improves the coarse-grid results, and (3) the traditional method works well in situations where better resolution of the refined grid has little influence on the overall flow-system dynamics, but if this is not true, lack of a feedback mechanism produced errors in head of up to 3.6 percent in the systems tested. Errors could be substantially larger for other systems.