MODFLOW

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MODFLOW simulation

MODFLOW is the U.S. Geological Survey modular finite-difference flow model, which is a computer code that solves the groundwater flow equation. The program is used by hydrogeologists to simulate the flow of groundwater through aquifers. The code is free software, written primarily in Fortran, and can compile and run on DOS, Windows or Unix-like operating systems.

3-dimensional grid

Since its original development in the early 1980s, the USGS have released five major releases, and is now considered to be the de facto standard code for aquifer simulation. Currently, there are at least four actively developed commercial and non-commercial graphical user interfaces for MODFLOW.

[edit] Groundwater flow equation

The governing partial differential equation used in MODFLOW is:

where

K_xx, K_yy and K_zz are the values of hydraulic conductivity along the x, y, and z coordinate axes (L/T)

h is the potentiometric head (L)

W is a volumetric flux per unit volume representing sources and/or sinks of water, where negative values are extractions, and positive values are injections (T^-1)

S_S is the specific storage of the porous material (L^-1); and

t is time (T)

[edit] Limitations

• The water must has a constant density, dynamic viscosity (and consequently temperature) throughout the modelling domain

• The principle components of anisotropy of the hydraulic conductivity used in MODFLOW is displayed on the right. This tensor does not allow non-orthogonal anisotropies, as could be expected from flow in fractures

[edit] Versions

Cover image from McDonald & Harbaugh (1984), which illustrates a computer surrounded by modules and arrays used by MODFLOW

[edit] MODFLOW (original version)

The first version was released on December 28, 1983 (McDonald & Harbaugh, 1984), and was coded entirely in FORTRAN 66. The source code for this version is not available on the internet.

[edit] MODFLOW-88

This version of MODFLOW was rewritten in FORTRAN 77, and was originally released in 1987 July 24. The current version of MODFLOW-88 is 2.6, released in 1996 September 20.

MODPATH, was initially developed in 1989 to post-process the steady-state MODFLOW-88 data to determine three-dimensional pathlines of particles. This innovation has been indispensable for the fields of contaminant hydrogeology. It is still used as a post-processor in recent versions of MODFLOW.

A separate program, MODFLOWP, was developed in 1992 to estimate various parameters used in MODFLOW. This program was eventually built into MODFLOW-2000.

[edit] MODFLOW-96

MODFLOW-96 (version 3.0) was originally released in 1996 December 3, and is a cleaned-up and revised continuation of MODFLOW-88. There are three final releases of MODFLOW-96:

• MODFLOW-96, version 3.3 (2000 May 2)
• MODFLOW-96h (with HYDMOD package), version 3.3h (2000 July 10)
• MODFLOWP (MODFLOW-96 with parameter-estimation), version 3.2 (1997 Oct 9)

Several graphical interfaces were first developed using the MODFLOW-96 code.

[edit] MODFLOW-2000

MODFLOW-2000 (version 1.0; version numbering was reset) was released on 2000 July 20, which merged MODFLOWP and HYDMOD codes into the main program. Many new packages and enhancements were also included, including new solvers, stream and saturated flow packages. The internal design concepts also changed from previous versions, such that packages, processes and modules are distinct. This version is coded in a mixture of FORTRAN 77, Fortran 90, and C. MODFLOW-2000 can also be compiled for parallel computing, which can allow multiple processors to be used to increase model complexity and/or reduce simulation time.

There are four current version of MODFLOW-2000:

• MODFLOW-2000 (or mf2k), version 1.17.01 (2006 September 22)
• MF2k-GWM, with groundwater management capability using optimization, version 1.0.3 (2006 January 21), based on mf2k 1.13
• MF2k-FMP, with Farm Process, version 1.00 (2006 May 19), based on mf2k 1.15.03
• MF2K-GWT, groundwater flow and solute-transport model, version 1.9 (2006 April 14), based on mf2k 1.16

[edit] MODFLOW-2005

This is the present development version of MODFLOW, and does not yet have a major commercial graphical interface. It is written primarily in Fortran 90 and C. The current versions include:

• MODFLOW-LGR with local grid refinement, version 1.0 (2006 March 1)
• MODFLOW-2005 version 1.2 (2006 October 16)

[edit] Packages

• ↑  due to licensing restrictions, the USGS is no longer able to publicly distribute the Algebraic Multi-Grid

[edit] Commercial graphical interfaces

There are several graphical commercial versions of MODFLOW, which include the compiled MODFLOW code with modifications. These programs aid the input of data for creating MODFLOW models, however there is limited compatibility between the programs.

• GMS - Groundwater Modeling System
• PMWIN - Processing MODFLOW (for Windows), freeware provided alongside a book
• Groundwater Vistas Publisher
• Groundwater Vistas
• Visual MODFLOW
• Argus ONE

All current versions of these products run only on Microsoft Windows, however previous versions of GMS (up to Version 3.1) were compiled for several Unix platforms.

The USGS has a free MODFLOW-GUI, which is updated often, however it requires a non-free version of Argus ONE.

[edit] References

• Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000, the U.S. Geological Survey modular ground-water model — User guide to modularization concepts and the Ground-Water Flow Process: U.S. Geological Survey Open-File Report 00-92, 121 p. [1]
• Harbaugh, A.W., and McDonald, M.G., 1996a, User's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 96-485, 56 p. PDF, PS.
• Harbaugh, A.W., and McDonald, M.G., 1996, Programmer's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 96-486, 220 p. PDF, PS.
• McDonald, M.G., and Harbaugh, A.W., 1984, A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 83-875, 528 p.
• McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water-Resources Investigations, book 6, chap. A1, 586 p. English, Chinese.

[edit] External links

• MODFLOW and related programs official website
• Online guide to MODFLOW-2000