MODFLOW

Criterion

Explanation

General Description

MODFLOW simulates groundwater flow using a finite difference equation solution to the groundwater flow equation.

Model Domain

The physical domain of the model includes the unsaturated and saturated zones.

Developer

US Geological Survey

Hardware computing requirements

The code has been used on UNIX-based computers and personal computers running various forms of the Microsoft Windows operating system.

Code language

Fortran. The most recent version, MODFLOW 6 was programmed in Fortran using a modern programming style. Many of the simulation components were programmed using an object-oriented design described in Adams and others (2009) provides a comprehensive description of the details for implementing object-oriented programming concepts using Fortran. The object-oriented design is different from the procedural program design that was used for previous MODFLOW versions.

Original application

The original MODFLOW model was developed in 1984 to simulate groundwater flow using a finite difference equation solution to the groundwater flow equation. It used a modular framework in which sententence not complete

Public/proprietary and cost

Public, no cost

Physically or empirically based

Physically based

Mathematical methods used

MODFLOW solves the groundwater flow equation using a finite-difference numerical solution.

Input data requirements

Hydraulic conductivity, storativity, boundary fluxes (recharge, lateral fluxes), boundary conditions (constant head, head-dependent boundary, etc.)

Outputs

Outputs include spatial distribution of heads, water budgets, and boundary flows.

Pre-processing and post-processing tools

Multiple pre-and post-processing programs can be used with MODFLOW. These include Visual MODFLOW (Waterloo Hydrogeologic), Groundwater Vistas (Rockware), USGS Model Muse and Model Viewer.

Representation of uncertainty

Uncertainty is represented through the results of sensitivity analysis which can be used to provide ranges of model outputs.

Prevalence

Of all the groundwater flow models widely available, MODFLOW, is regarded by many as the most widely used by government agencies and consultant firms (Loudyi et al. 2014).

Ease of use for public entities

There is a high level of use ease. The code is readily available for free. Training and support are readily available. Multiple graphic interfaces are available.

Ease of obtaining information and availability of technical support

There is substantial online information available through the USGS. The USGS continues to support MODFLOW with upgraded models and addition features. User groups exist.
Support is provided at the USGS 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 modflow@usgs.gov or by contacting Chris Langevin, Joe Hughes, or Ned Banta at:

Earth Systems Modeling Branch
Integrated Modeling and Prediction Division
Water Mission Area, U.S. Geological Survey
411 National Center
12201 Sunrise Valley Drive
Reston, VA 20192

Source code availability

The source code is available for modification if needed at

Status of model development

Whether the model is developed and available for immediate use; this may include models that continue to be updated. What is the future direction of model updates?This field was not completed

Uses in Delta

MODFLOW has been used in the Delta to simulate groundwater hydrologic conditions for the entire Delta (CVHM-D) to simulate groundwater resources impacts analysis for the BDCP EIR/EIS, and individual islands (e.g. Deverel et al. 2017).

Challenges for integration

For integration with surface water modeling, temporal and spatial scales and calculations associated with MODFLOW modeling are different that those used for surface water models.

The water must have a constant density, dynamic viscosity (and consequently temperature) throughout the modelling domain (SEAWAT is a modified version of MODFLOW which is designed for density-dependent groundwater flow and transport).

The principal components of anisotropy of the hydraulic conductivity tensor does not allow non-orthogonal anisotropies, as could be expected from flow in fractures.

Challenges for use in the Delta include correctly simulating island geometry using finite differences; simulating ET and drains can be also challenging. MODFLOW unstructured grids may be better suited.