GFLOW 2000

GFLOW 2000® is an analytic element code that belongs in the arsenal of commonly used groundwater modeling tools. It solves groundwater flow problems by superimposing analytic solutions under Dupuit-Forchheimer assumptions. In its most simple dress the code facilitates rapid construction and solution of a steady-state single-layer groundwater model containing multiple recharge and transmissivity zones with complicated internal boundary conditions. However, one of its most innovative aspects is its ability to perform conjunctive surface water/groundwater modeling. GFLOW 2000® uses stream networks to route baseflow so that available streamflow responds to stresses such as pumping, an option that is particularly useful in determining the effect of wells on the headwaters of streams. It has several ways of simulating the interaction of groundwater with lakes, including the ability to perform detailed water balances in the presence of through-flowing streams, a capacity not yet available in other analytic element codes or MODFLOW2000. Together these options make it particularly useful in modeling unconfined flow in terrains (e.g. glacial) with closely spaced surface-water bodies. A second innovation of the code is to facilitate use of the "stepwise" modeling approach. Often Dupuit-Forchheimer assumptions are more valid for regional flow problems than for site-specific problems where vertical head gradients are important. To allow the speed of analytic elements to be mated with the flexibility of finite-differences, GFLOW 2000® supports automatic conversion of part of its domain to a local MODFLOW model with flux or constant head boundary conditions around the inset grid. Once the conversion is made, the user can add more complexity to geometry and properties inside the MODFLOW model. Another advanced feature of the code is particle tracking that takes advantage of mass balance considerations to simulate flow lines from the water table below a stream to a well. There are "tricks" that are needed to most effectively perform analytic element modeling; the ample HELP material introduces the user to the technique's special vocabulary (e.g., "linesinks") and also provides a general guide to modeling, which makes the code a first-rate teaching tool. The GUI, compatible with all versions of Windowsâ, is workmanlike with excellent visualization tools related to surface water and calibration. A lot of thought has gone into converting readily available maps such as USGS coverages into base maps. GFLOW 2000® is available for $450 from: www.haitjema.com.

Last Update: February, 2004