MODFLOW

The governing partial differential equation for a confined aquifer used in MODFLOW is:

:$\backslash frac\{\backslash partial\}\{\backslash partial\; x\}\; \backslash left[\; K\_\{xx\}\; \backslash frac\{\backslash partial\; h\}\{\backslash partial\; x\}\; \backslash right]\; +\; \backslash frac\{\backslash partial\}\{\backslash partial\; y\}\; \backslash left[\; K\_\{yy\}\; \backslash frac\{\backslash partial\; h\}\{\backslash partial\; y\}\; \backslash right]\; +\; \backslash frac\{\backslash partial\}\{\backslash partial\; z\}\; \backslash left[\; K\_\{zz\}\; \backslash frac\{\backslash partial\; h\}\{\backslash partial\; z\}\; \backslash right]\; +\; W\; =\; S\_\{S\}\; \backslash frac\{\backslash partial\; h\}\{\backslash partial\; t\}$

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
• $t\backslash ,$ is time (T)

The finite difference form of the partial differential in a discretized aquifer domain (represented using rows, columns and layers) is:

:$\backslash begin\{align\}$

& \mathit{CR}_{i,j-\tfrac{1}{2},k}\left(h^m_{i,j-1,k}-h^m_{i,j,k}\right) +

\mathit{CR}_{i,j+\tfrac{1}{2},k}\left(h^m_{i,j+1,k}-h^m_{i,j,k}\right) + \\

& \mathit{CC}_{i-\tfrac{1}{2},j,k}\left(h^m_{i-1,j,k}-h^m_{i,j,k}\right) +

\mathit{CC}_{i+\tfrac{1}{2},j,k}\left(h^m_{i+1,j,k}-h^m_{i,j,k}\right) + \\

& \mathit{CV}_{i,j,k-\tfrac{1}{2}}\left(h^m_{i,j,k-1}-h^m_{i,j,k}\right) +

\mathit{CV}_{i,j,k+\tfrac{1}{2}}\left(h^m_{i,j,k+1}-h^m_{i,j,k}\right) + \\

& P_{i,j,k}\,h^m_{i,j,k} + Q_{i,j,k} = \mathit{SS}_{i,j,k}\left(\Delta r_j \Delta c_i \Delta v_k\right)

\frac{h^m_{i,j,k}-h^{m-1}_{i,j,k}}{t^m-t^{m-1}}

\end{align}

where

:$h^m\_\{i,j,k\}\backslash ,$ is the hydraulic head at cell i,j,k at time step m

:CV, CR and CC are the hydraulic conductances, or branch conductances between node i,j,k and a neighboring node

:$P\_\{i,j,k\}\backslash ,$ is the sum of coefficients of head from source and sink terms

:$Q\_\{i,j,k\}\backslash ,$ is the sum of constants from source and sink terms, where is flow out of the groundwater system (such as pumping) and $Q\_\{i,j,k\}>0.0\backslash ,$ is flow in (such as injection)

:$\backslash mathit\{SS\}\_\{i,j,k\}\backslash ,$ is the specific storage

:$\backslash Delta\; r\_j\backslash Delta\; c\_i\backslash Delta\; v\_k\backslash ,$ are the dimensions of cell i,j,k, which, when multiplied, represent the volume of the cell; and

:$t^m\backslash ,$ is the time at time step m

This equation is formulated into a system of equations to be solved as:

:$\backslash begin\{align\}$

&\mathit{CV}_{i,j,k-\tfrac{1}{2}} h^m_{i,j,k-1} +

\mathit{CC}_{i-\tfrac{1}{2},j,k} h^m_{i-1,j,k} +

\mathit{CR}_{i,j-\tfrac{1}{2},k} h^m_{i,j-1,k} \\

&+ \left(

- \mathit{CV}_{i,j,k-\tfrac{1}{2}} - \mathit{CC}_{i-\tfrac{1}{2},j,k} - \mathit{CR}_{i,j-\tfrac{1}{2},k}

- \mathit{CR}_{i,j+\tfrac{1}{2},k} - \mathit{CC}_{i+\tfrac{1}{2},j,k} - \mathit{CV}_{i,j,k+\tfrac{1}{2}}

+ \mathit{HCOF}_{i,j,k}\right) h^m_{i,j,k} \\

&+ \mathit{CR}_{i,j+\tfrac{1}{2},k} h^m_{i,j+1,k}

+ \mathit{CC}_{i+\tfrac{1}{2},j,k} h^m_{i+1,j,k}

+ \mathit{CV}_{i,j,k+\tfrac{1}{2}} h^m_{i,j,k+1}

= \mathit{RHS}_{i,j,k}

\end{align}

where

:$\backslash begin\{align\}$

\mathit{HCOF}_{i,j,k} &= P_{i,j,k} - \frac{\mathit{SS}_{i,j,k}\Delta r_j \Delta c_i \Delta_k}{t^m-t^{m-1}} \\

\mathit{RHS}_{i,j,k} &= -Q_{i,j,k} - \mathit{SS}_{i,j,k}\Delta r_j \Delta c_i \Delta v_k \frac{h^{m-1}_{i,j,k}}{t^m-t^{m-1}}

\end{align}

or in matrix form as:

:$A\backslash mathbf\{h\}=\backslash mathbf\{q\}$

where

:A is a matrix of the coefficients of head for all active nodes in the grid

:$\backslash mathbf\{h\}$ is a vector of head values at the end of time step m for all nodes in the grid; and

:$\backslash mathbf\{q\}$ is a vector of the constant terms, RHS, for all nodes of the grid.

• The water must have a constant density, dynamic viscosity (and consequently temperature) throughout the modelling domain ([http://water.usgs.gov/ogw/seawat/ SEAWAT] is a modified version of MODFLOW which is designed for density-dependent groundwater flow and transport)

• The principal 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. Horizontal anisotropy for an entire layer can be represented by the coefficient "TRPY" (Data Item 3 Page 153).{{cite book |author1=McDonald, M.G. |author2=Harbaugh, A.W. |name-list-style=amp |date=December 28, 1983 |title=A modular three-dimensional finite-difference ground-water flow model |publisher=U.S. Geological Survey |series=Open-File Report 83-875 |url=https://pubs.er.usgs.gov/usgspubs/ofr/ofr83875 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}

Image:modflow original.pngs used by MODFLOW. This was said at the time to resemble a "component stereo system".]]

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.

The first version of MODFLOW was published on December 28, 1983, and was coded entirely in FORTRAN 66. The source code for this version is listed in USGS Open File Report 83-875 referred to above.

This version of MODFLOW{{cite book |author1=McDonald, M.G. |author2=Harbaugh, A.W. |name-list-style=amp |year=1988 |title=A modular three-dimensional finite-difference ground-water flow model |publisher=U.S. Geological Survey |series=Techniques of Water-Resources Investigations, Book 6 |url=http://pubs.usgs.gov/twri/twri6a1/ |format=PDF}} was rewritten in FORTRAN 77, and was originally released on July 24, 1987. The current version of [http://water.usgs.gov/software/modflow-88.html 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.

MODFLOW-96 (version 3.0) was originally released on December 3, 1996, and is a cleaned-up and revised continuation of MODFLOW-88.{{cite book |author1=Harbaugh, A.W. |author2=McDonald, M.G. |name-list-style=amp |year=1996a |title=User's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model |publisher=U.S. Geological Survey |series=Open-File Report 96-485 |url=http://water.usgs.gov/software/code/ground_water/modflow/doc/ofr96485.pdf}}{{cite book |author1=Harbaugh, A.W. |author2=McDonald, M.G. |name-list-style=amp |year=1996 |title=Programmer's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model |publisher=U.S. Geological Survey |series=Open-File Report 96-486 |url=http://water.usgs.gov/software/code/ground_water/modflow/doc/ofr96486.pdf}} There are three final releases of MODFLOW-96:

• [http://water.usgs.gov/software/modflow-96.html MODFLOW-96] (version 3.3, May 2, 2000)
• [http://water.usgs.gov/nrp/gwsoftware/modflow/modflow-96h.htm MODFLOW-96h] (version 3.3h, July 10, 2000), with HYDMOD package
• [http://water.usgs.gov/software/Modflowp.html MODFLOWP] (version 3.2, Oct 9, 1997), MODFLOW-96 with parameter-estimation

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

MODFLOW-2000 (version 1.0; version numbering was reset) was released on July 20, 2000, which merged MODFLOWP and HYDMOD codes into the main program and has integrated observation, sensitivity analysis, parameter estimation, and uncertainty evaluation capabilities.{{cite book |author=Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G. |year=2000 |title=MODFLOW-2000, the U.S. Geological Survey modular ground-water model — User guide to modularization concepts and the Ground-Water Flow Process |publisher=U.S. Geological Survey |series=Open-File Report 00-92 |url=http://water.usgs.gov/nrp/gwsoftware/modflow2000/ofr00-92.pdf}} 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 was coded in a mixture of FORTRAN 77, Fortran 90, and one solver was programmed in 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. The parallelization capability is designed to support the sensitivity analysis, parameter estimation, and uncertainty analysis capabilities of MODFLOW-2000.

The final version of [http://water.usgs.gov/nrp/gwsoftware/modflow2000/modflow2000.html MODFLOW-2000] (or MF2K) is version 1.19.01, released on March 25, 2010. There are four related or branched codes based on MODFLOW-2000:

• [http://water.usgs.gov/nrp/gwsoftware/mf2k-gwm/MF2K-GWM.html MF2K-GWM or GWM-2000] (version 1.1.4, May 31, 2011, branched from mf2k 1.17.2), with groundwater management capability using optimization
• [http://water.usgs.gov/nrp/gwsoftware/mf2k-fmp/mf2kfmp.html MF2K-FMP] (version 1.00, May 19, 2006, based on mf2k 1.15.03), with Farm Process
• [http://water.usgs.gov/nrp/gwsoftware/mf2k_gwt/mf2k_gwt.html MF2K-GWT] (version 1.9.8, October 28, 2008, based on MF2K 1.17.02), groundwater flow and solute-transport model
• [http://water.usgs.gov/ogw/seawat/ SEAWAT] (version 4.00.05, October 19, 2012), variable-density flow and transport processes
• [http://water.usgs.gov/nrp/gwsoftware/mf2k_vsf/vsf.html VSF] (version 1.01, July 5, 2006), variably saturated flow

MODFLOW-2005 {{cite book |first=Arlen W. |last=Harbaugh |title=MODFLOW-2005, The U.S. Geological Survey Modular Ground-Water Model—the Ground-Water Flow Process |publisher=U.S. Geological Survey |year=2005 |series=Techniques and Methods 6–A16 |url=http://pubs.usgs.gov/tm/2005/tm6A16/}} differs from MODFLOW-2000 in that the sensitivity analysis, parameter estimation, and uncertainty evaluation capabilities are removed. Thus, the support for these capabilities now falls to "clip on" codes that are supported externally to the MODFLOW support effort. In addition, the code was reorganized to support multiple models within one MODFLOW run, as needed for the [https://water.usgs.gov/ogw/modflow-lgr LGR] (Local Grid Refinement) capability.{{cite book |first=Steffen |last=Mehl |title=MODFLOW-2005, The U.S. Geological Survey Modular Ground-Water Model—Documentation of Shared Node Local Grid Refinement (LGR) and the Boundary Flow and Head (BFH) Package |publisher=U.S. Geological Survey |year=2005 |series=Techniques and Methods 6–A12 |url=http://pubs.usgs.gov/tm/2005/tm6A12/ }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }} MODFLOW-2005 is written primarily in Fortran 90 and C, with C being used for one solver.

The current version of [https://water.usgs.gov/ogw/modflow/mf2005.html MODFLOW-2005] is version 1.12.00, released on February 3, 2017. Related or branched codes include:

• [http://water.usgs.gov/ogw/cfp/cfp.htm MODFLOW-CFP] (version 1.8.00, February 23, 2011), conduit flow process to simulate turbulent or laminar groundwater flow conditions
• [http://water.usgs.gov/ogw/modflow-lgr/ MODFLOW-LGR] (version 2.0, September 19, 2013), local grid refinement
• [http://water.usgs.gov/nrp/gwsoftware/mf2005_gwm/MF2005-GWM.html GWM-2005] (version 1.4.2, March 25, 2013), groundwater management capability using optimization
• [http://water.usgs.gov/nrp/gwsoftware/mf2005_fmp/mf2005_fmp.html MF2005-FMP2] (version 1.0.00, October 28, 2009), estimate dynamically integrated supply-and-demand components of irrigated agriculture as part of the simulation of surface-water and ground-water flow
• [http://water.usgs.gov/ogw/modflow-nwt/ MODFLOW-NWT](version 1.1.3, August 1, 2017), Newton formulation for solving problems involving drying and rewetting nonlinearities of the unconfined groundwater-flow equation.{{Citation |chapter=MODFLOW-NWT, A Newton Formulation for MODFLOW-2005 |year=2011 |author1=Niswonger, Richard G. |author2=Panday, Sorab |author3=Ibaraki, Motomu |title=Techniques and Methods |publisher=U.S. Geological Survey |publication-place=Reston, VA |chapter-url=https://pubs.er.usgs.gov/publication/tm6A37 |series=Techniques and Methods 6-A37|doi=10.3133/tm6A37 }}
• [https://www.usgs.gov/software/modflow-owhm-one-water-hydrologic-flow-model MODFLOW-OWHMv1]{{Citation |chapter=One-Water Hydrologic Flow Model (MODFLOW-OWHM) |year=2014 |author1=Hanson, Randall T. |author2=Boyce, Scott E. |author3=Schmid, Wolfgang |author4=Hughes, Joseph D. |author5=Mehl, Steffen W. |author6=Leake, Stanley A. |author7=Maddock, Thomas, III |author8=Niswonger, Richard G. |title=Techniques and Methods |publisher=U.S. Geological Survey |publication-place=Reston, VA |chapter-url=https://pubs.er.usgs.gov/publication/tm6A51 |series=Techniques and Methods 6-A51|page=134 |doi=10.3133/tm6A51 |doi-access=free }} (version 1.00.12, October 1, 2016), The One-Water Hydrologic Flow Model (MF-OWHM1{{Cite web|url=https://sourceforge.net/projects/modflow-owhm|title=Mf-Owhm | Modflow Owhm|date=9 April 2020 }}), developed cooperatively between the USGS and the U.S. Bureau of Reclamation, is a fusion of multiple versions of MODFLOW-2005 (NWT, LGR, FMP, SWR, SWI) into ONE version, contains upgrades and new features and allows the simulation of head-dependent flows, flow-dependent flows, and deformation dependent flows that collectively affect conjunctive use of water resources.
• [https://water.usgs.gov/ogw/mfusg/ MODFLOW-USG]. All version of MODFLOW listed above are constructed on what is called a structured grid. That is, the grid is composed of rectilinear blocks. The only exception is the LGR capability, which allows locally refined grids to be inserted into the structure of a "parent" grid. The local area is again composed of rectilinear blocks, but the blocks are smaller. Experimentation with a much more flexible grid structure resulted in the release of [https://water.usgs.gov/ogw/mfusg/ MODFLOW-USG]{{Citation |title=MODFLOW–USG Version 1: An Unstructured Grid Version of MODFLOW for Simulating Groundwater Flow and Tightly Coupled Processes Using a Control Volume Finite-Difference Formulation |year=2013 |author1=Panday, Sorab |author2=Langevin, Christian D. |author3=Niswonger, Richard G. |author4=Ibaraki, Motomu |author5=Hughes, Joseph D. |journal=USGS Report |publisher=U.S. Geological Survey |publication-place=Reston, VA |url=http://pubs.usgs.gov/tm/06/a45/ |series=Techniques and Methods 6-A45|page=44 |doi=10.3133/tm6A45 |bibcode=2013usgs.rept...44P }} (version 1.3.00, December 1, 2015), designed to be adapted to a wide range of grid variations using unstructured grids. MODFLOW-USG has similar capabilities as MODFLOW 6, which provides grid capabilities with and intermediate level of flexibility.
• [https://www.gsienv.com/usg-transport/ MODFLOW-USG Transport]. An update of MODFLOW USG including multiple solute species transport, density dependent flow and transport, use of the Richard's equation for flow and transport in the unsaturated zone and air-water interface sorption. Some of the updates to the model have also been made to accommodate for transport of PFAS.Panday, Sorab (2024); USG-Transport Version 2.4.0: Transport and Other Enhancements to MODFLOW-USG, GSI Environmental, http://www.gsi-net.com/en/software/free-software/USG-Transport.html {{Cite journal |last1=Hort |first1=Hiroko M. |last2=Stockwell |first2=Emily B. |last3=Newell |first3=Charles J. |last4=Scalia |first4=Joseph |last5=Panday |first5=Sorab |date=2024 |title=Modeling and Evaluation of PFOS Retention in the Unsaturated Zone above the Water Table |url=https://ngwa.onlinelibrary.wiley.com/doi/10.1111/gwmr.12662 |journal=Groundwater Monitoring & Remediation |language=en |volume=44 |issue=3 |pages=38–48 |doi=10.1111/gwmr.12662 |bibcode=2024GMRed..44c..38H |issn=1069-3629}}

MODFLOW 6 (MF6), first released in 2017, is the sixth core version of MODFLOW to be released by the USGS.{{cite book |first1=Joseph D. |last1=Hughes |first2=Christian D. |last2=Langevin |first3=Edward R. |last3=Banta |title=Techniques and Methods |year=2017 |chapter=Documentation for the MODFLOW 6 framework |series=Techniques and Methods 6-A57 |doi=10.3133/tm6A57 |page=40}} This release is a rewrite of MODFLOW following an object-oriented programming paradigm in Fortran, and provides a platform that includes the capabilities from several previous MODFLOW-2005 versions, including MODFLOW-NWT, MODFLOW-USG, and MODFLOW-LGR.{{cite book |first1=Christian D. |last1=Langevin |first2=Joseph D. |last2=Hughes |first3=Edward R. |last3=Banta |first4=Richard G. |last4=Niswonger |first5=Sorab |last5=Panday |first6=Alden M. |last6=Provost |title=Techniques and Methods |year=2017 |chapter=Documentation for the MODFLOW 6 Groundwater Flow Model |series=Techniques and Methods 6-A55 |doi=10.3133/tm6A55}} MODFLOW 6 supports structured or unstructured grids, has full support for the Newton-Raphson formulation, and has a unique Water Mover Package that allows flows to be routed between the advanced packages, including the Streamflow Routing, Lake, Multi-Aquifer Well, and Unsaturated Zone Flow Packages. MODFLOW 6 also contains a Groundwater Transport (GWT) model that simulates transient three-dimensional solute transport on structured or unstructured grids and through the advanced flow and mover packages. An Application Programming Interface (API) is also available for MODFLOW 6, which allows the program to be coupled with other models or controlled with popular scripting languages, such as Python. While there are a few features lacking in the current release that are supported in MODFLOW-2005, most of the popular capabilities in previous MODFLOW versions are available in MODFLOW 6. The current version is 6.2.2, released July 30, 2021.{{Cite web|url=https://www.usgs.gov/software/modflow-6-usgs-modular-hydrologic-model|title=MODFLOW 6: USGS Modular Hydrologic Model}}

The MODFLOW One-Water Hydrologic Flow Model version 2{{Cite report |chapter-url=https://pubs.usgs.gov/publication/tm6A60 |chapter=One-Water Hydrologic Flow Model: A MODFLOW based conjunctive-use simulation software |last1=Boyce |first1=Scott E. |last2=Hanson |first2=Randall T. |last3=Ferguson |first3=Ian |last4=Schmid |first4=Wolfgang |last5=Henson |first5=Wesley R. |last6=Reimann |first6=Thomas |last7=Mehl |first7=Steffen W. |last8=Earll |first8=Marisa M. |title=Techniques and Methods |date=2020 |publisher=U.S. Geological Survey |issue=6–A60 |doi=10.3133/tm6a60 |language=en|doi-access=free }} ([https://www.usgs.gov/software/modflow-one-water-hydrologic-flow-model-mf-owhm MF-OWHM]) is a major rewrite of MF-OWHM1 released in 2020.Boyce, S.E., 2020, MODFLOW One-Water Hydrologic Flow Model (MF-OWHM) Conjunctive Use and Integrated Hydrologic Flow Modeling Software, version 2.0.0: U.S. Geological Survey Software Release, https://doi.org/10.5066/P9P8I8GS MF-OWHM is a MODFLOW-2005 based integrated hydrologic model designed for the analysis of conjunctive-use management. The term “integrated” refers to the tight coupling of groundwater flow, surface-water flow, landscape processes, aquifer compaction and subsidence, reservoir operations, and conduit (karst) flow. This fusion results in a simulation software capable of addressing water-use and sustainability problems, including conjunctive-use, water-management, water-food-security, and climate-crop-water scenarios.{{Cite web |date=2020-04-07 |title=MODFLOW One-Water Hydrologic Flow Model (MF-OWHM) {{!}} U.S. Geological Survey |url=https://www.usgs.gov/software/modflow-one-water-hydrologic-flow-model-mf-owhm |access-date=2025-03-18 |website=www.usgs.gov |language=en}}

As a second core version of MODFLOW-2005, MF-OWHM maintains backward compatibility with existing MODFLOW-2005 versions. Existing models developed using MODFLOW-2005, MODFLOW-NWT, MODFLOW-SWI,{{Cite report |url=https://pubs.usgs.gov/publication/tm6A46 |title=Documentation of the seawater intrusion (SWI2) package for MODFLOW |last1=Bakker |first1=Mark |last2=Schaars |first2=Frans |last3=Hughes |first3=Joseph D. |last4=Langevin |first4=Christian D. |last5=Dausman |first5=Alyssa M. |date=2013 |publisher=U.S. Geological Survey |issue=6–A46 |language=en}} MODFLOW-SWR,{{Cite report |url=https://pubs.usgs.gov/publication/tm6A40 |title=Documentation of the Surface-Water Routing (SWR1) Process for modeling surface-water flow with the U.S. Geological Survey Modular Ground-Water Model (MODFLOW-2005) |last1=Hughes |first1=Joseph D. |last2=Langevin |first2=Christian D. |last3=Chartier |first3=Kevin L. |last4=White |first4=Jeremy T. |date=2012 |publisher=U.S. Geological Survey |issue=6–A40 |pages=i–113 |language=en}} MODFLOW-LGR,{{Cite report |url=https://pubs.usgs.gov/publication/tm6A44 |title=MODFLOW–LGR—Documentation of ghost node local grid refinement (LGR2) for multiple areas and the boundary flow and head (BFH2) package |last1=Mehl |first1=Steffen W. |last2=Hill |first2=Mary C. |date=2013 |publisher=U.S. Geological Survey |issue=6–A44 |language=en}} and MODFLOW-CFPShoemaker, W.B., Kuniansky, E.L., Birk, S., Bauer, S., and Swain, E.D., 2008, Documentation of a Conduit Flow Process (CFP) for MODFLOW-2005: U.S. Geological Survey Techniques and Methods, Book 6, Chapter A24, 50 p., https://pubs.usgs.gov/tm/tm6a24/ can also be simulated using MF-OWHM. The Farm Process (FMP)Schmid, Wolfgang, and Hanson, R.T., 2009, The Farm Process Version 2 (FMP2) for MODFLOW-2005—Modifications and Upgrades to FMP1: U.S. Geological Survey Techniques and Methods 6-A-32, 102 p., https://pubs.usgs.gov/tm/tm6a32/ is part of MF-OWHM but is the only component that does not maintain input backward compatibility with past releases (see the [https://code.usgs.gov/modflow/mf-owhm FMP_Template] for new input structure). MF-OWHM also includes a Surface Water Operations ModuleFerguson, I.M.., Llewellyn, D., Hanson, R.T., and Boyce S.E., 2016, User guide to the surface water operations process—An integrated approach to simulating large-scale surface water management in MODFLOW-based hydrologic models: Denver, Colo., Bureau of Reclamation Technical Memorandum no. 86-68210–2016-02, 96 p. (SWO) with a Fortran-like scripting language, [https://code.usgs.gov/modflow/mf-owhm/-/tree/develop/src/slang Slang], that can specify dynamic reservoir and stream operations. A current major application of MF-OWHM, developed by the USGS, is the California Central Valley (CVHM2).{{Cite journal |last1=Faunt |first1=Claudia C. |last2=Traum |first2=Jonathan A. |last3=Boyce |first3=Scott E. |last4=Seymour |first4=Whitney A. |last5=Jachens |first5=Elizabeth R. |last6=Brandt |first6=Justin T. |last7=Sneed |first7=Michelle |last8=Bond |first8=Sandra |last9=Marcelli |first9=Marina F. |date=2024-04-22 |title=Groundwater Sustainability and Land Subsidence in California's Central Valley |journal=Water |language=en |volume=16 |issue=8 |pages=1189 |doi=10.3390/w16081189 |doi-access=free |bibcode=2024Water..16.1189F |issn=2073-4441 }}

The current USGS [https://www.usgs.gov/products/software/software-management/types-software-review Approved Software] version is [https://code.usgs.gov/modflow/mf-owhm/-/tree/2.3.0 2.3.0]Boyce, S.E., 2024, MODFLOW One-Water Hydrologic Flow Model (MF-OWHM) Conjunctive Use and Integrated Hydrologic Flow Modeling Software, version 2.3.0: U.S. Geological Survey Software Release, https://doi.org/10.5066/P9P8I8GSBoyce, S.E. and Ferguson, I.M., 2024, MODFLOW One-Water Hydrologic Flow Model (MF-OWHM) Conjunctive Use and Integrated Hydrologic Flow Modeling Software with Surface Water Operations, version 2.3.0: U.S. Geological Survey Software Release, https://doi.org/10.5066/P9P8I8GS released on January 15, 2024, and current preliminary-beta release of [https://code.usgs.gov/modflow/mf-owhm/-/tree/2.3.1-b4 2.3.1b-4]Boyce, S.E., 2025, MODFLOW One-Water Hydrologic Flow Model (MF-OWHM) Conjunctive Use and Integrated Hydrologic Flow Modeling Software, version 2.3.1-b4: U.S. Geological Survey Software Release, https://doi.org/10.5066/P9P8I8GS released on February 27, 2025.

The names in this table are the labels used to turn MODFLOW capabilities on and off via a key input file. Most capabilities have many alternatives or can be omitted, but the ones related to the BASIC Package are always required. Many of the capabilities introduced are supported in later versions, though the grid change enabled with MODFLOW-USG and MODFLOW 6 meant that such backward compatibility was rather selective.

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

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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.

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

• [http://water.usgs.gov/nrp/gwsoftware/ModelMuse/ModelMuse.html ModelMuse] is a grid-independent graphical user interface from the USGS for MODFLOW 6, MODPATH, SUTRA, and PHAST version 1.51. There are no license restrictions. The source code is included.
• [https://github.com/modflowpy/flopy FloPy] is a Python package for creating, running, and post-processing MODFLOW-based models.
• [http://water.usgs.gov/nrp/gwsoftware/mfgui4/modflow-gui.html MODFLOW-GUI] – Made by the USGS: it is updated often to match the current USGS MODFLOW development. It supports MODFLOW-96, MODFLOW-2000, MODFLOW-2005, MODPATH, ZONEBUDGET, GWT, MT3DMS, SEAWAT, and GWM. Source code for MODFLOW-GUI is included. It depends on [http://www.argusone.com/ Argus ONE]: a commercial interface for constructing generic models. There are no license restrictions beyond those of Argus ONE.
• [http://www.pmwin.net/ PMWIN] – "Processing MODFLOW" (for Windows) – powerful freeware for MODFLOW processing and visualization, provided alongside an instructional book;{{cite book |author=Wen-Hsing Chiang |title=3D-Groundwater Modeling with PMWIN |year=2005 |edition=Second |publisher=Springer |isbn=978-3-540-27590-9 |doi=10.1007/3-540-27592-4}} also available in Traditional Chinese. The license for this version is limited to non-commercial use.
• [http://code.google.com/p/mflab/ mflab] - mflab is a MATLAB interface to MODFLOW. The user builds and analyzes models by writing a set of MATLAB scripts. This results in flexible and efficient workflows, allowing a great deal of automation.
• [http://oss.deltares.nl/web/imod/home iMOD] - Free and open source interface developed by [https://www.deltares.nl/en/ Deltares]. iMOD contains an accelerated version of MODFLOW with fast, flexible and consistent sub-domain modeling techniques. Facilitating large, high resolution MODFLOW modeling and geo-editing of the subsurface
• [http://www.freewat.eu/ FREEWAT] is a free and open source, QGIS-integrated modelling platform integrating MODFLOW (MODFLOW versions integrated are MODFLOW-2005 and MODFLOW-OWHM) and the following MODFLOW-related simulation codes: [https://hydro.geo.ua.edu/mt3d/index.htm MT3DMS], [https://water.usgs.gov/ogw/mt3d-usgs/ MT3D-USGS], [https://water.usgs.gov/ogw/seawat/ SEAWAT], [https://water.usgs.gov/nrp/gwsoftware/zonebud3/zonebudget3.html ZONE BUDGET], [https://water.usgs.gov/ogw/modpath/ MODPATH], [http://igwmc.mines.edu/freeware/ucode/ UCODE-2014]. FREEWAT has been developed in the framework of the H2020 FREEWAT project (FREE and open source software tools for WATer resource management), financed by the EU Commission under the call WATER INNOVATION: BOOSTING ITS VALUE FOR EUROPE. The source code is released under a [https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html GNU GENERAL PUBLIC LICENSE, Version 2, June 1991], along with a complete set of User Manuals and tutorials.

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 US$7000. This is a list of commercial programs for MODFLOW:

• [http://www.argusone.com/ Argus ONE]
• GMS – Groundwater Modeling System
• [http://www.groundwatermodels.com/ESI_Software.php Groundwater Vistas]
• [http://www.leapfrog3d.com/products/leapfrog-hydro Leapfrog Hydro]
• [http://www.simcore.com Processing Modflow]
• 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.

• Graphic Groundwater – Windows-based interface
• ModelCad – A Windows-based interface, developed by Geraghty and Miller, Inc.
• [http://www.mpassociates.gr/software/environment/modime.html ModIME] – A DOS-based interface by S.S. Papadopulos & Associates, Inc.

• FEFLOW
• [https://www.acricfd.com/software/porflow/default.htm PORFLOW]
• HydroGeoSphere
• Hydrological optimization
• MIKE SHE
• MT3D

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Category:Hydrology models

Category:Hydrogeology software

Category:United States Geological Survey

Category:Geology software for Linux

Category:Public-domain software

Category:Free science software