MODFLOW - 2000

SOFTWARE REVIEW by Eileen Poeter,

IGWMC, Colorado School of Mines (Golden, CO)

 

MODFLOW2000 (MF2K) is the most recent version of the U.S. Geological Survey (USGS) public domain MODFLOW software for simulating flow in saturated porous media in three dimensions with a finite difference grid.

A Geraghty and Miller survey of more than 5,000 groundwater modelers conducted in 1993 indicated MODFLOW was the most widely used groundwater model in the world. More than 23,000 copies of MODFLOW were downloaded from the main USGS web site from 1990 to 2000. Its popularity has continued, in part due to the modularity of the program and the resulting ability of USGS and others to add capabilities.

In contrast to previous versions of MODFLOW, MF2K includes observation, sensitivity and parameter-estimation options with a convenient "Parameter" approach that facilitates model setup. A wide range of conditions can be represented using "Packages," including many recently-released new packages: The Hydrogeologic-Unit Flow (HUF) Package facilitates connection with hydrogeologic framework models such as EarthVision by populating the model grid with hydraulic parameters using defined hydrogeologic units. The Multi-Node Well (MNW) Package distributes flow in wells that intersect multiple model layers (for horizontal or angled wells, multiple nodes) and accounts for reduced pumpage caused by drawdown at the pumping well. The Geometric Multi-Grid (GMG) Package is efficient for solving large problems and is the first part of MODFLOW to be written in C rather than FORTRAN. The StreamFlow-Routing (SFR, replaces STR) Package routes surface water to streams and lakes, adjusting the river stage as stream discharge changes, such that flux to and from the groundwater system adjusts to the changing stage. The Subsidence and Aquifer-System Compaction (SUB3) Package simulates elastic compaction and expansion, and inelastic compaction of compressible fine-grained beds within the aquifer. Unsaturated Flow Packages are due out soon.

Some simple pre- and post-processing programs for MF2K are available from the USGS. These include MF2KI, a graphical user interface; GW_CHART, a program for evaluating model fit to observations and sensitivity analysis; and ModelViewer, a program to contour simulated heads. More powerful capabilities are available in a variety of interfaces that require purchase of commercial products. These can be found by searching for "MODFLOW interface" using a Web search engine. These programs facilitate construction of input files and assessment of results, but they do not support the latest MF2K capabilities, and errors in user understanding or bugs in the interfaces can yield misleading results.

Familiarity with the MODFLOW text files is important for trouble shooting, for using new MF2K features, and for dealing with unusual modeling situations. The new online guide of the USGS MF2K Web page provides a quick way to look up options and input formats. Download documentation, source code, and executables of MF2K and associated programs at no charge and view the NEW! comprehensive online guide at water.usgs.gov/nrp/gwsoftware/modflow2000/modflow2000.html.