MODFLOW 6: USGS Modular Hydrologic Model

For nearly 40 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

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MODFLOW 6 is an object-oriented program and framework developed to provide a platform for supporting multiple models and multiple types of models within the same simulation (Hughes and others, 2017; Langevin and others, 2024). 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 MODFLOW 6 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. 

Supported Model Types

MODFLOW 6 presently contains four types of hydrologic models: 

• the Groundwater Flow (GWF) Model
• the Groundwater Transport (GWT) Model
• the Groundwater Energy (GWE) Model
• the Particle Tracking (PRT) Model

The Groundwater Flow (GWF) model for MODFLOW 6 simulates three-dimensional, transient, groundwater flow.  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.  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. There are packages for internal calculations of groundwater flow, packages for representing hydrologic stresses (constant heads, wells, recharge, rivers, general head boundaries, drains, and evapotranspiration), and advanced stress packages (streamflow routing, lakes, multi-aquifer wells, and unsaturated zone flow), including an additional package for moving water available in one package into the individual features of the advanced stress packages.

The Groundwater Transport (GWT) model for MODFLOW 6 simulates three-dimensional transport of a single solute species in flowing groundwater. The GWT Model solves the solute transport equation using numerical methods and a generalized CVFD approach, which can be used with regular MODFLOW grids or with unstructured grids. The GWT Model is designed to work with most of the new capabilities released with the GWF Model, including the Newton flow formulation, unstructured grids, advanced packages, and the movement of water between packages. The GWF and GWT Models operate simultaneously during a MODFLOW 6 simulation to represent coupled groundwater flow and solute transport. The GWT Model can also run separately from a GWF Model by reading the heads and flows saved by a previously run GWF Model. The GWT model is also capable of working with the flows from another groundwater flow model, provided the flows from that model can be written in the correct form to flow and head files. Advective transport can also be simulated in advanced stress packages and coupled to groundwater transport. If the GWF Model that provides the flow field for a GWT Model uses the Water Mover (MVR) Package to connect flow packages, then transport between these packages can also be represented by activating the Mover Transport (MVT) Package.

The Groundwater Energy (GWE) Model for MODFLOW 6 simulates three-dimensional transport of thermal energy in flowing groundwater based on a generalized control-volume finite-difference approach. The GWE Model is designed to work with the Groundwater Flow (GWF) Model for MODFLOW 6, which simulates transient, three-dimensional groundwater flow. The GWE Model simulates (1) advective transport, (2) the combined hydrodynamic dispersion processes of velocity-dependent mechanical dispersion and thermal conduction in groundwater, (3) thermal conduction in the solid aquifer material, (4) storage of thermal energy in the ground- water and solid aquifer material, (5) thermal equilibration between the groundwater and solid aquifer material, (5) zero-order decay or production of thermal energy in the groundwater and the solid, (6) mixing from groundwater sources and sinks, and (7) direct addition or removal of thermal energy. Advective energy transport can also be simulated in advanced stress packages, such as streams, lakes, multi- aquifer wells, and the unsaturated zone. If the GWF Model that provides the flow field for a GWE Model uses the Water Mover (MVR) Package to connect flow packages, then energy transport between these packages can also be represented by activating the Mover Energy Transport (MVE) Package. 

The Particle Tracking (PRT) Model for MODFLOW 6 calculates three-dimensional, advective particle trajectories in flowing groundwater. The PRT Model is designed to work with the Groundwater Flow (GWF) Model (Langevin and others, 2017) for MODFLOW 6, which simulates transient, three-dimensional groundwater flow. The PRT Model replicates much of the functionality of MODPATH 7 and offers support for a much broader class of unstructured grids. The PRT model uses the same spatial discretization used by the GWF Model, which may be represented using either a structured (DIS) or an unstructured (DISV) grid. The PRT Model can be run in the same simulation as the associated GWF Model or in a separate simulation that reads previously calculated flows from a binary budget file. The current version of the PRT Model does not support grids of DISU type, tracking of particles through advanced stress package features such as lakes or streams reaches, or exchange of particles between PRT models. The PRT Model simulates the forward tracking of particles; however, backward particle tracking is possible using a procedure described here for reversing simulated flows from a previous GWF simulation and using those flows as input to PRT.

Capabilities in the Current Release

This current MODFLOW 6 release synthesizes many of the capabilities in existing MODFLOW variants:

• MODFLOW-2005 — the GWF Model contains revisions of the commonly used flow packages, stress packages, and advanced stress packages
• MODFLOW-NWT — the GWF Model supports an optional Newton-Raphson approach for water table aquifers
• MODFLOW-USG — GWF Models can be developed using regular MODFLOW grids or unstructured grids
• MODFLOW-LGR — any number of GWF Models can be specified for a single simulation; these GWF Models are tightly coupled at the matrix level
• MODFLOW-CDSS — multiple stress and advanced stress packages of the same type can be specified for a single GWF Model
• MT3D/MT3D-USGS — the GWT Model simulates solute transport for a single chemical species
• SEAWAT — the GWF Model contains a Buoyancy Package for simulating variable-density groundwater flow.  Fluid density can be calculated from concentrations in a coupled GWT Model
• MODPATH 7 – the PRT Model simulates advective particle tracking in a groundwater flow field

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

Five USGS publications documenting MODFLOW 6 are included in the software distribution:

• 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.
• Langevin, C.D., Provost, A.M., Panday, Sorab, and Hughes, J.D., 2022, Documentation for the MODFLOW 6 Groundwater Transport Model: U.S. Geological Survey Techniques and Methods, book 6, chap. A61, 56 p., https://doi.org/10.3133/tm6A61.
• Hughes, J.D., Leake, S.A., Galloway, D.L., and White, J.T., 2022, Documentation for the Skeletal Storage, Compaction, and Subsidence (CSUB) Package of MODFLOW 6: U.S. Geological Survey Techniques and Methods, book 6, chap. A62, 57 p., https://doi.org/10.3133/tm6A62.

Additional publications on MODFLOW 6 include

• Provost, A.M., Bardot, K., Langevin, C.D., McCallum, J.L., 2025, Accurate Simulation of Flow through Dipping Aquifers with MODFLOW 6 Using Enhanced Cell Connectivity. Groundwater, https://doi.org/10.1111/gwat.13459.
• Morway, E.D., Provost, A.M., Langevin, C.D., Hughes, J.D., Russcher, M.J., Chen, C.Y., Lin, Y.F.F., 2025, A New Groundwater Energy Transport Model for the MODFLOW Hydrologic Simulator. Groundwater, https://doi.org/10.1111/gwat.13470.
• Langevin, C.D., Panday, S, and Provost, A.M., 2020, Hydraulic-head formulation for density-dependent flow and transport: Groundwater, v. 58, no. 3, p. 349–362, https://doi.org/10.1111/gwat.12967.
• Morway, E.D., Langevin, C.D., and Hughes, J.D., 2021, Use of the MODFLOW 6 water mover package to represent natural and managed hydrologic connections: Groundwater, v. 59, no. 6, p. 913-924, https://doi.org/10.1111/gwat.13117.
• Hughes, J.D., Russcher, M.J., Langevin, C.D., Morway, E.D., and McDonald, R.R., 2022, The MODFLOW Application Programming Interface for simulation control and software interoperability: Environmental Modelling & Software, v. 148, 105257, https://doi.org/10.1016/j.envsoft.2021.105257.
• Langevin, C.D., Hughes, J.D., Provost, A.M., Russcher, M.J. and Panday, S., 2023, MODFLOW as a Configurable Multi-Model Hydrologic Simulator: Groundwater, v. 62, p. 111-123, https://doi.org/10.1111/gwat.13351.
• Larsen, J.D., Langevin, C.D., Hughes, J.D. and Niswonger, R.G. (2024), An Agricultural Package for MODFLOW 6 Using the Application Programming Interface. Groundwater, v. 62, p. 157-166, https://doi.org/10.1111/gwat.13367.

Download Current Version of MODFLOW 6

Current and previous versions of MODFLOW 6 can be downloaded from the public MODFLOW 6 Repository.  The following are included in each release:

• Release Notes - description of changes since the last release.
• Distribution - a compressed zip file containing documentation, binary executables, source code, test problems, and utility programs.  Distributions are available for several different operating systems. Distributions for the Extended Version of MODFLOW 6 (supporting parallel simulation and NetCDF input and output) are also available.
• Input and Output Guide -  description of all model input and output.

Programs Related to MODFLOW 6

The USGS also has developed several programs that can be used to assist with MODFLOW 6 simulations.

• ZONEBUDGET for MODFLOW 6
  A program for computing detailed subregional water budgets for GWF models and advanced stress packages. This program is based on ZONEBUDGET for MODFLOW-2000 and MODFLOW-2005. ZONEBUDGET for MODFLOW 6 is included in the MODFLOW 6 release.
• Mf5to6 Converter 
  A program for converting MODFLOW-2005, MODFLOW-NWT, and MODFLOW-LGR model datasets to MODFLOW 6 datasets. Mf5to6 is included in the MODFLOW 6 release.
• MODPATH version 7
  MODPATH is a particle-tracking post-processing model that computes flow paths using output from MODFLOW.
• GRIDGEN
  GRIDGEN is a program for generating layered quadtree grids for MODFLOW-USG.
• FloPy
  FloPy is a Python package for creating, running, and post-processing MODFLOW-based models.
• ModelMuse
  ModelMuse is a graphical user interface for creating, running, and post-processing MODFLOW-based models as well as several other types of model.
• ModelViewer for MODFLOW 6
  ModelViewer for MODFLOW 6 is a graphical user interface for visualizing MODFLOW 6 model grids, input data, and output in three dimensions.

Previous MODFLOW Core Versions

Supported Versions

The following previous Core Versions of MODFLOW are provided by the USGS but are no longer actively developed:

• MODFLOW-2005

Superseded Versions

The following software is not actively supported by the USGS. The software has been superseded by MODFLOW 6. The software versions below are provided online for historical reference only, and the pages may contain outdated information or broken links.

• MODFLOW-2000
• MODFLOW-96
• MODFLOW-88

Find MODFLOW-Related Software

Visit the MODFLOW and Related Programs page for a list of MODFLOW-related software.

How to Cite MODFLOW 6

This USGS software has two citations associated with it.

1. The software citation is for MODFLOW 6.  This digital object identifier (DOI) is for the USGS location where the software resides.
2. The software release citation is for the software/code itself (now referred to by USGS as a "Software Release") and references a specific version of the code and associated release date. This DOI links to the code.

In instances where an author is citing use of this software, it would be appropriate to cite one or more of the references listed in the MODFLOW 6 Publications section as well as both the MODFLOW 6 software and the specific software release version that was used.

Software Citation for MODFLOW 6

Langevin, C.D., Hughes, J.D., Banta, E.R., Provost, A.M., Niswonger, R.G., and Panday, Sorab, 2017, MODFLOW 6 Modular Hydrologic Model: U.S. Geological Survey Software, https://doi.org/10.5066/F76Q1VQV

Software/Code Citation for the Current Version

In addition to the general software citation for MODFLOW 6, each MODFLOW 6 release has a software release citation.  Version-specific software release citations can be found at the MODFLOW 6 Repository.