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,^[1] the USGS have released four major releases, and is now considered to be the de facto standard code for aquifer simulation. Currently, there are at least five 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 (SEAWAT-2000 is a modified version of MODFLOW-2000 which is designed for density-dependent groundwater flow and transport)

• 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. Furthermore, if the older BCF package is used (explained below), K_xx = K_yy, which assumes that there is no horizontal anisotropy.

[edit] Versions

Cover image from McDonald & Harbaugh (1983)^[2], which illustrates a computer surrounded by modules and arrays used by MODFLOW. This was said at the time to resemble a "component stereo system".

[edit] "Modular Model"

The USGS throughout the 1970s had developed several hundred models, written in different dialects of FORTRAN. At the time, it was common practice to rewrite a new model to fit the need of a new groundwater scenario. The concept for MODFLOW was originally designed in 1981 to provide a common modular groundwater model, which could be compiled on multiple platforms without major (or any) modification, and can read and write common formats. Different aspects of the groundwater system would be handled using the modules, similar to the idea of a "component stereo system". The original name of the code was "The USGS Modular Three-Dimensional Finite-Difference Ground-Water Flow Model", or informally as "The Modular Model." The name MODFLOW was coined several years after the initial code development, which started in 1981.^[1]

The first version of MODFLOW^[2] was published on December 28, 1983, and was coded entirely in FORTRAN 66. This version was not publicly released, so the source code for this version is unavailable.

[edit] MODFLOW-88

This version of MODFLOW^[3] was rewritten in FORTRAN 77, and was originally released on July 24, 1987. The current version of MODFLOW-88 is 2.6, released on September 20, 1996.

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.^[4][5] 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.^[6] 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 1.17.02 (2007 February 14)
• 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] Graphical user interfaces

There are several graphical interfaces to MODFLOW, which often include the compiled MODFLOW code with modifications. These programs aid the input of data for creating MODFLOW models.

[edit] Non-commercial interfaces

Non-commercial MODFLOW versions are free, however, their licensing usually limit the use to non-profit educational or research purposes.

• MODFLOW-GUI (which depends on Argus ONE, which is a commercial interface for constructing generic models) – Made by the USGS, and is updated often to match the current USGS MODFLOW development.
• PMWIN – "Processing MODFLOW" (for Windows) – powerful freeware for MODFLOW processing and visualization, provided alongside an instructional book;^[7] also available in Traditional Chinese. The license for this version is limited to non-commercial use.

[edit] Commercial programs

Commercial MODFLOW programs are typically used by governments and consultants for practical applications of MODFLOW to real-world groundwater problems. Professional versions of MODFLOW are generally priced at a minimum of around $1000 and typically range upward to $7000 USD. This is a list of commercial programs for MODFLOW:

• GMS – Groundwater Modeling System
• Groundwater Vistas Publisher
• Groundwater Vistas
• PMWIN Pro – Same as non-Pro version,^[7] but licensing compatible for commercial use
• Visual MODFLOW

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

[edit] Former graphical interfaces

• Graphic Groundwater – Windows-based interface
• ModelCad – A Windows-based interface, developed by Geraghty and Miller, Inc.
• ModIME – A DOS-based interface by S.S. Papadopulos & Associates, Inc.

[edit] References

1. ^ ^{a b} McDonald M.G. and Harbaugh, A.W. (2003). "The History of MODFLOW". Ground Water 41 (2): 280–283. DOI:10.1111/j.1745-6584.2003.tb02591.x. 
2. ^ ^{a b} McDonald, M.G., and Harbaugh, A.W. (December 28, 1983). A modular three-dimensional finite-difference ground-water flow model, Open-File Report 83-875. U.S. Geological Survey, 528 p. 
3. ^ McDonald, M.G., and Harbaugh, A.W. (1988). "Chapter A1", A modular three-dimensional finite-difference ground-water flow model (PDF), Techniques of Water-Resources Investigations, Book 6, U.S. Geological Survey, 586 p. 
4. ^ 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, Open-File Report 96-485. U.S. Geological Survey, 56 p. 
5. ^ 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, Open-File Report 96-486. U.S. Geological Survey, 220 p. 
6. ^ 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, Open-File Report 00-92. U.S. Geological Survey, 121 p. 
7. ^ ^{a b} Wen-Hsing Chiang (2005). 3D-Groundwater Modeling with PMWIN, Second edition, Springer, 397 p. DOI:10.1007/3-540-27592-4. ISBN 978-3-540-27590-9. 

[edit] External links

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