NCF: A Finite‐Element Computer Program to Simulate Ground‐Water Flow Within the U.S. Geological Survey Modular Ground‐Water Flow Model (MODFLOW)

Abstract

AbstractA finite‐element package has been developed for the U.S. Geological Survey Modular Ground‐Water Flow Model, MODFLOW (McDonald and Harbaugh, 1988). The package, entitled the Node Centered Flow (NCF) Package, offers alternatives for constructing and solving ground‐water flow problems. As with MODFLOW's Block Centered Flow (BCF) package, NCF uses a finite‐difference solution for vertical flow, but unlike BCF it uses a 2d Galerkin finite‐element solution for flow within a layer. The algorithm used in NCF is described in Neuman et al. (1982). This technique permits simulation within a layer of off‐diagonal elements in the (2 × 2) transmissivity or hydraulic conductivity tensor. The most advantageous feature of the NCF Package is the capability for designing a nonrectangular grid. User specification of the horizontal (x, y) coordinates of individual nodes allows model features such as meandering stream channels, faults, and wells to be more precisely represented. NCF uses the same input style as BCF and will be immediately familiar to MODFLOW users; BCF input files are also easily converted to NCF input files. NCF parameters are input by layer, row, and column, allowing NCF and BCF to work with all of the same MODFLOW packages with the exception of matrix solving packages.