MODFLOW

Purpose

MODFLOW is a modular hydrologcial model that allows users to simulate and project groundwater condition and groundwater/surface-water interaction to inform management and policy decisions for the sustainable and productive use of these water resources.

Description

MODFLOW is the USGS's modular hydrologic model. MODFLOW is a popular open-source groundwater flow model considered an international standard for simulating and predicting groundwater conditions and groundwater/surface-water interactions. The model has been in use for over 30 years with continued refinement driven by the growing need to understand surface and ground water interactions.

MODFLOW was originally developed and released solely as a groundwater-flow simulation code when first published in 1984. The models 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.

The newest version of MODFLOW (Version 6 - August 2018) provides both a Groundwater Flow Model (GFM) and a Modelling Framework. The MODFLOW 6 Framework allows developers to add both new models and interactions between the models. It provides a platform for supporting multiple models of different types within the same simulation i.e. the linking of regional scale groundwater models with a regional scale model, or the linking of surface water models with ground water models.

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. The model allows you to develop a numerical representation (groundwater model) of the hydrogeological environment given defined spatial extents. Users can define the model grid using:
1.    a regular MODFLOW grid consisting of layers, rows, and columns,
2.    a layered grid defined by (x, y) vertex pairs, or
3.    a general unstructured grid based on concepts developed for MODFLOW-USG.

Conceptually 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 those related to internal calculations of groundwater flow (discretization, initial conditions, hydraulic conductance, and storage), stress packages (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). An additional package is also available for moving water available in one package into the individual features of the advanced stress packages.

MODFLOW 6 is a new object-oriented program and underlying Framework was developed to provide a platform for supporting multiple models and multiple types of models within the same simulation.

Within the MODFLOW Framwork 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. The transfer of information between models is isolated to exchange objects in the programming, which allow models to be developed and used independently of one another.

Also 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.

For additional overview information see "New to MODFLOW? Start Here!" page on USGS Website.

 

Latest Version	MODFLOW 6.0.3 released August 2018
State of Development	Released and updated

Scope

Outcome Areas	Environmental
Management Domains	Freshwater
Subdomains	Water Quantity/Flows, Water Quality
Intended End Users	Researcher Regional Council Scientist
Steady State or Dynamic	Unknown

Input & Output Data

Accessibility

Open/Closed Source	Open Source

User Information

Operating Systems	MS Windows
Software Needed	Command Line free to download - but these codes are often then run in commercial third-party user interfaces such as Groundwater Vistas, GMS or Visual MODFLOW.
User Interface	No user interface
Ease of Use	Moderate
Use in Policy Process	Plan (Policy Formulation), Review (Issue Identification)
Documentation	Documentation for the MODFLOW 6 Groundwater flow model Documentation for MODFLOW6 framework

Technical Considerations

Programming Language	FORTRAN
Analytical Techniques	Input/output
Model Structure
Keywords	Groundwater flow, groundwater surface-water interactions, solute transport, aquifer
Links	MODFLOW - USGS Homepage USGS home page of MODFLOW: https://water.usgs.gov/ogw/modflow/MODFLOW.html Documentation for the MODFLOW 6 framework:  https://pubs.er.usgs.gov/publication/tm6A57  What is MODFLOW?: https://www.waterloohydrogeologic.com/2012/06/22/what-is-modflow/
Key References	Barlow, P.M., and Harbaugh, A.W., 2006, USGS Directions in MODFLOW Development (Ground Water) (80KB PDF) Harbaugh, A.W., 2005, MODFLOW-2005, The U.S. Geological Survey modular ground-water model – the Ground-Water Flow Process (TM 6-A16)   Also see USGS Groundwater Information - Publication Page for more

Associated Case Studies