USGS Groundwater Information
MODFLOW 6: USGS Modular Hydrologic Model
MODFLOW is a popular open-source groundwater flow model distributed by the U.S. Geological Survey. For over 30 years, the MODFLOW program has been widely used by academics, private consultants, and government scientists to accurately, reliably, and efficiently simulate groundwater flow. With time, growing interest in surface and groundwater interactions, local refinement with nested and unstructured grids, karst groundwater flow, solute transport, and saltwater intrusion, has led to the development of numerous MODFLOW versions. Although these MODFLOW versions are often based on the core MODFLOW version (previously MODFLOW-2005), there are often incompatibilities that restrict their use with other MODFLOW versions. In many cases, development of these alternative MODFLOW versions has been challenging due to the underlying program structure, which was designed for the simulation of a single groundwater flow model using a regular MODFLOW grid consisting of layers, rows, and columns.
Overview of MODFLOW 6
This figure shows a triangular grid in which the size of the triangular cells is reduced in areas with relatively large hydraulic gradients, such as around the shoreline of a lake, near pumping wells, and along a stream. This type of layered grid can be represented using the Discretization by Vertices (DISV) Package in MODFLOW 6. Credit: USGS. Image is in the public domain. View larger figure.
A new object-oriented program and underlying framework called MODFLOW 6 was developed to provide a platform for supporting multiple models and multiple types of models within the same simulation. This version of MODFLOW is labeled with a "6" because it is the sixth core version of MODFLOW to be released by the USGS (previous core versions were released in 1984, 1988, 1996, 2000, and 2005). In the new design, any number of models can be included in a simulation. These models can be independent of one another with no interaction, they can exchange information with one another, or they can be tightly coupled at the matrix level by adding them to the same numerical solution. Transfer of information between models is isolated to exchange objects, which allow models to be developed and used independently of one another. Within this new framework, a regional-scale groundwater model may be coupled with multiple local-scale groundwater models. Or, a surface-water flow model could be coupled to multiple groundwater flow models. The framework naturally allows for future extensions to include the simulation of solute transport.
Groundwater Flow (GWF) Model
MODFLOW 6 presently contains one type of hydrologic model, the Groundwater Flow (GWF) Model. The GWF Model for MODFLOW 6 is based on a generalized control-volume finite-difference (CVFD) approach in which a cell can be hydraulically connected to any number of surrounding cells. Users can define the model grid using
For complex problems involving water-table conditions, an optional Newton-Raphson formulation, based on the formulations in MODFLOW-NWT and MODFLOW-USG, can be activated. The GWF Model is divided into "packages," as was done in previous MODFLOW versions. A package is the part of the model that deals with a single aspect of simulation. Packages included with the GWF Model include
An additional package is also available for moving water available in one package into the individual features of the advanced stress packages. The GWF Model also has packages for obtaining and controlling output from the model.
XT3D Flow Formulation
A new groundwater flow formulation was developed specifically for the GWF Model in MODFLOW 6. This new flow formulation is called the XT3D option. The XT3D option extends the capabilities of MODFLOW by enabling simulation of fully three-dimensional anisotropy on regular or irregular grids in a way that properly takes into account the full, three-dimensional hydraulic conductivity tensor. It can also improve the accuracy of groundwater flow simulations in cases in which the model grid violates certain geometric requirements. Thus, the XT3D option is an alternative to the Ghost-Node Correction (GNC) Package, which was developed for MODFLOW-USG.
In addition to the many new or redesigned capabilities, the MODFLOW 6 input structure has also been redesigned. Within package input files, information is divided into blocks and informative keywords are used to label numeric data and activate options. This new input structure was designed to make it easier for users to adjust simulation options in an intuitive manner, reduce user input errors, and allow new capabilities to be added without causing problems with backward compatibility.
Capabilities in the Initial Release
This first MODFLOW 6 release with the GWF Model synthesizes many of the capabilities in existing MODFLOW variants:
For MODFLOW users with existing models, the MODFLOW 6 distribution includes a conversion program that will translate a MODFLOW-2005, MODFLOW-NWT, or MODFLOW-LGR (Version 2) model into the MODFLOW 6 format.
MODFLOW 6 Publications
Three USGS publications documenting MODFLOW 6 are included in the software distribution:
Current Version: MODFLOW 6 Version 6.0.2
The current version of MODFLOW 6 is version 6.0.2, released February 23, 2018. For a complete explanation of the changes in this release and a history of past releases, refer to:
Users are encouraged to provide written feedback to the points of contact listed below.
Downloads and Documentation
Note: Users are encouraged to read the documents provided in the 'doc' directory of this software distribution.
How to Cite
This USGS software has two citations associated with it.
In instances where an author is citing use of this software, it would be appropriate to cite both the report documenting the code and the specific software release version that was used.
Report Citations for MODFLOW 6
Hughes, J.D., Langevin, C.D., and Banta, E.R., 2017, Documentation for the MODFLOW 6 framework: U.S. Geological Survey Techniques and Methods, book 6, chap. A57, 40 p., https://doi.org/10.3133/tm6A57.
Langevin, C.D., Hughes, J.D., Banta, E.R., Niswonger, R.G., Panday, Sorab, and Provost, A.M., 2017, Documentation for the MODFLOW 6 Groundwater Flow Model: U.S. Geological Survey Techniques and Methods, book 6, chap. A55, 197 p., https://doi.org/10.3133/tm6A55.
Provost, A.M., Langevin, C.D., and Hughes, J.D., 2017, Documentation for the "XT3D" option in the Node Property Flow (NPF) Package of MODFLOW 6: U.S. Geological Survey Techniques and Methods, book 6, chap. A56, 40 p., https://doi.org/10.3133/tm6A56.
Software/Code Citation for MODFLOW 6 v.6.0.2
Langevin, C.D., Hughes, J.D., Banta, E.R., Provost, A.M., Niswonger, R.G., and Panday, Sorab, 2018, MODFLOW 6 Modular Hydrologic Model version 6.0.2: U.S. Geological Survey Software Release, 23 February 2018, https://doi.org/10.5066/F76Q1VQV
Related MODFLOW 6 Programs
The USGS also has developed several programs that can be used to assist with MODFLOW 6 simulations.
Previous MODFLOW Core Versions
The following previous Core Versions of MODFLOW are still actively supported by the USGS.
The following software is not actively supported by the USGS. The software has been superseded by MODFLOW-2005. The software versions below are provided online for historical reference only, and the pages may contain outdated information or broken links.
Point of Contact
Support is provided for correcting bugs and clarification of how MODFLOW 6 is intended to work. Only limited assistance can be provided for applying MODFLOW 6 to specific problems by emailing firstname.lastname@example.org or by contacting:
Earth Systems Modeling Branch
Other USGS Groundwater Software
The USGS develops groundwater, water-quality, surface-water, and other water-resources software for use by the USGS in fulfilling its mission. Most of this software is available online for download at no charge.
Disclaimers and Notices
This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use. Also refer to the USGS Water Resources Software User Rights Notice for complete use, copyright, and distribution information.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Software License and Purchase Information
This software is a product of the U.S. Geological Survey, which is part of the U.S. Government.
This software is freely distributed. There is no fee to download and (or) use this software.
Users do not need a license or permission from the USGS to use this software. Users can download and install as many copies of the software as they need.
As a work of the United States Government, this USGS product is in the public domain within the United States. You can copy, modify, distribute, and perform the work, even for commercial purposes, all without asking permission. Additionally, USGS waives copyright and related rights in the work worldwide through CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/ ).
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