MODFLOW and Related Programs

Science Center Objects

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. The previous core version, MODFLOW-2005, is actively maintained and supported as well.

Example visualization of MODFLOW output.

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 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 Mission Area, and there are advanced versions. 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, but MODFLOW-2005 (the previous core version) is still actively maintained and supported. Advanced MODFLOW versions include specialized MODFLOW variants and versions of MODFLOW that use newer formulations. These advanced MODFLOW versions are also available from the USGS.

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 the release of MODFLOW-2000 by the addition of "Processes," which are defined as parts of the code that solve a major equation or set of related equations and that consist of sets of the underlying packages. The part of the code that solves the groundwater-flow equation became the Groundwater Flow (GWF) Process. Although additional processes have been developed for MODFLOW, the GWF Process remains a core process on which other MODFLOW simulation capabilities are built. The primary change in MODFLOW-2005 from MODFLOW-2000 is the approach used by MODFLOW-2005 for managing internal data.

MODFLOW 6 is the newest core version and uses a new format of blocks and keywords for input of model data. It was written from scratch using an object-oriented design. MODFLOW 6 presently supports one type of process model — the GWF Model. Other models may be added in the future, such as a groundwater transport model, a surface-water model, and a pipe network model, for example. 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. MODFLOW 6 is an entirely new version of MODFLOW.

Core Versions

MODFLOW Variants: Newer, specialized, or advanced versions of MODFLOW 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.
  • 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.


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. 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

Most 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-2005 guide can be found online. An online guide is not presently available for MODFLOW 6; an up-to-date user guide is included in the MODFLOW 6 distribution.


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:

  1. reading the report documenting the initial release of MODFLOW 6
  2. reviewing materials on the MODFLOW software page, and running the test problems available for download with MODFLOW


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.

Public Domain

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 ( ).



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.