MODFLOW is the USGS's modular hydrologic model. MODFLOW is considered an international standard for simulating and predicting groundwater conditions and groundwater/surface-water interactions. MODFLOW 6 is presently the core MODFLOW version distributed by the USGS.
Originally developed and released solely as a groundwater-flow simulation code when first published in 1984, MODFLOW's modular structure has provided a robust framework for integration of additional simulation capabilities that build on and enhance its original scope. The family of MODFLOW-related programs now includes capabilities to simulate coupled groundwater/surface-water systems, solute transport, variable-density flow (including saltwater), aquifer-system compaction and land subsidence, parameter estimation, and groundwater management.
MODFLOW Development Plans, April 25, 2025
The USGS Water Mission Area actively develops and supports the MODFLOW suite of programs. Ongoing efforts are focused on providing maintenance and support for the core version of MODFLOW, called MODFLOW 6. Current development efforts are focused on improving parallel simulation capabilities, better integrating NetCDF for model input and output, and adding new hydrologic process models, such as models to simulate overland and channel surface water flow and transport. The USGS plans to continue these development efforts to meet the needs of the USGS, our stakeholders, and the needs of the hydrologic modeling community. Users are encouraged to track MODFLOW developments through our version-controlled MODFLOW 6 repository.
MODFLOW Versions
The USGS releases multiple versions of MODFLOW. This page focuses on MODFLOW versions that are part of USGS water enterprise software that is funded, developed, and maintained by the USGS Water Resources Mission Area. There is a core MODFLOW version, which is developed and maintained by the USGS Water Resources Mission Area. The core MODFLOW version is the one that is under active development and is often the most widely used and most thoroughly tested version. MODFLOW 6 is presently the core MODFLOW version distributed by the USGS. Other MODFLOW versions distributed by the USGS include specialized MODFLOW variants and versions of MODFLOW that use alternative formulations.
There have been six major releases of the core MODFLOW version: MODFLOW-84, MODFLOW-88, MODFLOW-96, MODFLOW-2000, MODFLOW-2005, and MODFLOW 6. The first three versions of the code, MODFLOW-84, MODFLOW-88 and MODFLOW-96, were based on the initial conceptualization of the program as a groundwater-flow model only. Specific aspects of a groundwater-flow system are simulated by these codes by use of independent, modular-programming components called "Packages," such as the Well Package and River Package. MODFLOW's modular design was further expanded with subsequent versions to represent additional processes.
MODFLOW 6 is the newest core version and uses a format of blocks and keywords for input of model data. It was written from scratch using an object-oriented design. MODFLOW 6 presently supports four different process models — groundwater flow, solute transport, heat transport, and particle tracking. Other models may be added in the future. Underlying MODFLOW 6 is a framework that allows developers to add new models and the interactions between models. A key feature of the new MODFLOW 6 framework is the ability to solve multiple, tightly coupled, numerical models in a single system of equations. These may be multiple models of the same type or of different types (Hughes and others, 2017; Langevin and others, 2024).
Core Versions
- MODFLOW 6: current core version
- MODFLOW-2005: previous core version (not actively developed)
MODFLOW 2005 Variants: Specialized versions for use by experienced modelers
- MODFLOW-NWT: MODFLOW-NWT uses a Newton-Raphson formulation to improve solution of unconfined groundwater-flow problems.
- MODFLOW-USG: MODFLOW-USG uses an unstructured-grid approach to simulate groundwater flow and tightly coupled processes using a control volume finite-difference formulation.
- GSFLOW: GSFLOW is a coupled groundwater and surface-water flow model based on the USGS Precipitation-Runoff Modeling System (PRMS), MODFLOW-2005, and MODFLOW-NWT.
- GWM: The Groundwater Management (GWM) Process for MODFLOW-2000 and MODFLOW-2005 is used to simulate groundwater management
MODFLOW-Based Particle Tracking and Solute Transport
- MODPATH: MODPATH is a particle-tracking post-processing model that computes flow paths using output from MODFLOW.
- MT3D-USGS: MT3D-USGS is a groundwater solute transport simulator for MODFLOW.
- SEAWAT: SEAWAT is a combined version of MODFLOW and MT3DMS for simulation of variable-density groundwater flow and transport.
Parameter Estimation and Uncertainty Analysis
- PEST++: PEST++ is an objected-oriented universal parameter estimation code written in C++ that can be used to calibrate MODFLOW models.
MODFLOW Utilities, Post Processors, and Graphical User Interfaces (GUIs)
- FloPy: FloPy is a Python package for creating, running, and post-processing MODFLOW-based models.
- GRIDGEN: GRIDGEN is a program for generating layered quadtree grids for MODFLOW-USG.
- GW Chart: GW_Chart is a graphing application for MODFLOW, Zonebudget, and other codes. GW_Chart also converts binary cell-by-cell flow files to text files.
- ModelMuse: ModelMuse is a GUI for MODFLOW 6, MODFLOW-2005, MODFLOW-LGR, MODFLOW-NWT, MODFLOW-CFP, MODFLOW-LGR, MODFLOW-OWHM, MT3DMS, MT3D-USGS, SUTRA, WellFootprint, PHAST, MODPATH, and ZONEBUDGET.
- ModelViewer: Model Viewer is a program for 3D visualization of groundwater-model results.
- ZONEBUDGET: ZONEBUDGET is a program for computing subregional water budgets for MODFLOW.
Links to additional MODFLOW related software, including legacy and superseded software, are available through the USGS Water Resources Groundwater Software page.
Running MODFLOW
MODFLOW is a command line executable program written in FORTRAN that reads ASCII text and binary input files and writes ASCII text and binary output files. MODFLOW will not run without user-generated input files. Although experienced MODFLOW users may be able to create MODFLOW input files by hand, most MODFLOW users rely on a graphical user interface (GUI) to prepare the input files and post-process the output files. The MODFLOW program itself does not generate contour plots or any other type of graphical output. These plots must be generated from MODFLOW results using other software programs. The USGS distributes several free pre- and post-processors for MODFLOW. Commercial GUIs are also available for sale by private vendors.
Online MODFLOW Guide
MODFLOW versions are periodically updated. Some of these updates include changes to the format of the input and output files. These changes are described with release notes that are distributed with each program. The USGS also provides online guides for several MODFLOW versions. These online guides contain up-to-date input instructions and other helpful information. The MODFLOW 6 guide can be found online, and an up-to-date user guide is included in the MODFLOW 6 distribution. The MODFLOW-2005 guide (and other MODFLOW-2005 variants) also can be found online.
Where to Go From Here
Successful use of MODFLOW typically requires a college-level modeling course or professional training on groundwater modeling. In some situations, the USGS can provide training to governmental agencies with a cooperative agreement with the USGS; agencies can contact their cooperating USGS office for additional information. MODFLOW courses are also offered by several private companies. Those with groundwater modeling experience can download MODFLOW. For instructions on MODFLOW installation, please refer to the section "Installation and Execution" in the MODFLOW 6 Release Notes, provided with the download.
While training is recommended, those interested in self-study are encouraged to begin by:
- reading the report documenting the initial release of MODFLOW 6
- reviewing materials on the MODFLOW software page, and running the test problems available for download with MODFLOW
MODFLOW is the USGS's modular hydrologic model. MODFLOW is considered an international standard for simulating and predicting groundwater conditions and groundwater/surface-water interactions. MODFLOW 6 is presently the core MODFLOW version distributed by the USGS.
Originally developed and released solely as a groundwater-flow simulation code when first published in 1984, MODFLOW's modular structure has provided a robust framework for integration of additional simulation capabilities that build on and enhance its original scope. The family of MODFLOW-related programs now includes capabilities to simulate coupled groundwater/surface-water systems, solute transport, variable-density flow (including saltwater), aquifer-system compaction and land subsidence, parameter estimation, and groundwater management.
MODFLOW Development Plans, April 25, 2025
The USGS Water Mission Area actively develops and supports the MODFLOW suite of programs. Ongoing efforts are focused on providing maintenance and support for the core version of MODFLOW, called MODFLOW 6. Current development efforts are focused on improving parallel simulation capabilities, better integrating NetCDF for model input and output, and adding new hydrologic process models, such as models to simulate overland and channel surface water flow and transport. The USGS plans to continue these development efforts to meet the needs of the USGS, our stakeholders, and the needs of the hydrologic modeling community. Users are encouraged to track MODFLOW developments through our version-controlled MODFLOW 6 repository.
MODFLOW Versions
The USGS releases multiple versions of MODFLOW. This page focuses on MODFLOW versions that are part of USGS water enterprise software that is funded, developed, and maintained by the USGS Water Resources Mission Area. There is a core MODFLOW version, which is developed and maintained by the USGS Water Resources Mission Area. The core MODFLOW version is the one that is under active development and is often the most widely used and most thoroughly tested version. MODFLOW 6 is presently the core MODFLOW version distributed by the USGS. Other MODFLOW versions distributed by the USGS include specialized MODFLOW variants and versions of MODFLOW that use alternative formulations.
There have been six major releases of the core MODFLOW version: MODFLOW-84, MODFLOW-88, MODFLOW-96, MODFLOW-2000, MODFLOW-2005, and MODFLOW 6. The first three versions of the code, MODFLOW-84, MODFLOW-88 and MODFLOW-96, were based on the initial conceptualization of the program as a groundwater-flow model only. Specific aspects of a groundwater-flow system are simulated by these codes by use of independent, modular-programming components called "Packages," such as the Well Package and River Package. MODFLOW's modular design was further expanded with subsequent versions to represent additional processes.
MODFLOW 6 is the newest core version and uses a format of blocks and keywords for input of model data. It was written from scratch using an object-oriented design. MODFLOW 6 presently supports four different process models — groundwater flow, solute transport, heat transport, and particle tracking. Other models may be added in the future. Underlying MODFLOW 6 is a framework that allows developers to add new models and the interactions between models. A key feature of the new MODFLOW 6 framework is the ability to solve multiple, tightly coupled, numerical models in a single system of equations. These may be multiple models of the same type or of different types (Hughes and others, 2017; Langevin and others, 2024).
Core Versions
- MODFLOW 6: current core version
- MODFLOW-2005: previous core version (not actively developed)
MODFLOW 2005 Variants: Specialized versions for use by experienced modelers
- MODFLOW-NWT: MODFLOW-NWT uses a Newton-Raphson formulation to improve solution of unconfined groundwater-flow problems.
- MODFLOW-USG: MODFLOW-USG uses an unstructured-grid approach to simulate groundwater flow and tightly coupled processes using a control volume finite-difference formulation.
- GSFLOW: GSFLOW is a coupled groundwater and surface-water flow model based on the USGS Precipitation-Runoff Modeling System (PRMS), MODFLOW-2005, and MODFLOW-NWT.
- GWM: The Groundwater Management (GWM) Process for MODFLOW-2000 and MODFLOW-2005 is used to simulate groundwater management
MODFLOW-Based Particle Tracking and Solute Transport
- MODPATH: MODPATH is a particle-tracking post-processing model that computes flow paths using output from MODFLOW.
- MT3D-USGS: MT3D-USGS is a groundwater solute transport simulator for MODFLOW.
- SEAWAT: SEAWAT is a combined version of MODFLOW and MT3DMS for simulation of variable-density groundwater flow and transport.
Parameter Estimation and Uncertainty Analysis
- PEST++: PEST++ is an objected-oriented universal parameter estimation code written in C++ that can be used to calibrate MODFLOW models.
MODFLOW Utilities, Post Processors, and Graphical User Interfaces (GUIs)
- FloPy: FloPy is a Python package for creating, running, and post-processing MODFLOW-based models.
- GRIDGEN: GRIDGEN is a program for generating layered quadtree grids for MODFLOW-USG.
- GW Chart: GW_Chart is a graphing application for MODFLOW, Zonebudget, and other codes. GW_Chart also converts binary cell-by-cell flow files to text files.
- ModelMuse: ModelMuse is a GUI for MODFLOW 6, MODFLOW-2005, MODFLOW-LGR, MODFLOW-NWT, MODFLOW-CFP, MODFLOW-LGR, MODFLOW-OWHM, MT3DMS, MT3D-USGS, SUTRA, WellFootprint, PHAST, MODPATH, and ZONEBUDGET.
- ModelViewer: Model Viewer is a program for 3D visualization of groundwater-model results.
- ZONEBUDGET: ZONEBUDGET is a program for computing subregional water budgets for MODFLOW.
Links to additional MODFLOW related software, including legacy and superseded software, are available through the USGS Water Resources Groundwater Software page.
Running MODFLOW
MODFLOW is a command line executable program written in FORTRAN that reads ASCII text and binary input files and writes ASCII text and binary output files. MODFLOW will not run without user-generated input files. Although experienced MODFLOW users may be able to create MODFLOW input files by hand, most MODFLOW users rely on a graphical user interface (GUI) to prepare the input files and post-process the output files. The MODFLOW program itself does not generate contour plots or any other type of graphical output. These plots must be generated from MODFLOW results using other software programs. The USGS distributes several free pre- and post-processors for MODFLOW. Commercial GUIs are also available for sale by private vendors.
Online MODFLOW Guide
MODFLOW versions are periodically updated. Some of these updates include changes to the format of the input and output files. These changes are described with release notes that are distributed with each program. The USGS also provides online guides for several MODFLOW versions. These online guides contain up-to-date input instructions and other helpful information. The MODFLOW 6 guide can be found online, and an up-to-date user guide is included in the MODFLOW 6 distribution. The MODFLOW-2005 guide (and other MODFLOW-2005 variants) also can be found online.
Where to Go From Here
Successful use of MODFLOW typically requires a college-level modeling course or professional training on groundwater modeling. In some situations, the USGS can provide training to governmental agencies with a cooperative agreement with the USGS; agencies can contact their cooperating USGS office for additional information. MODFLOW courses are also offered by several private companies. Those with groundwater modeling experience can download MODFLOW. For instructions on MODFLOW installation, please refer to the section "Installation and Execution" in the MODFLOW 6 Release Notes, provided with the download.
While training is recommended, those interested in self-study are encouraged to begin by:
- reading the report documenting the initial release of MODFLOW 6
- reviewing materials on the MODFLOW software page, and running the test problems available for download with MODFLOW