MODFLOW

MODFLOW is a widely used computer-based groundwater flow model developed by the United States Geological Survey (USGS). It is designed to simulate three-dimensional groundwater flow in layered aquifers using the finite-difference method and Darcy's law. The program has become a standard tool in hydrogeology for evaluating aquifer response to stresses.

Since its initial release in the late 1980s, MODFLOW has undergone several major revisions and variants, including MODFLOW-96, MODFLOW-2000, MODFLOW-2005, MODFLOW-NWT, MODFLOW-LGR, and MODFLOW-6. Each version introduces new features while preserving the modular, package-based approach that enables flexible modeling of diverse systems.

MODFLOW is organized as a modular framework. A basic discretization (DIS) defines the grid and time stepping, while the Layer Property Flow (LPF) package handles hydraulic properties and flow between layers. The model also includes boundary-condition and stress packages such as WEL for wells, RCH for recharge, RIV for rivers, DRN for drains, CHD and GHB for head controls, and SFR in some variants for streamflow routing.

Applications of MODFLOW span groundwater-resource management, contaminant transport assessment when coupled with solute-transport tools, climate and land-use impact analysis, and water-supply planning. It supports scenario testing, pumping strategies, recharge changes, and aquifer storage evaluations under varying boundary conditions.

MODFLOW-6 represents the current generation, combining capabilities of earlier variants into a single, more interoperable framework. It emphasizes stability, compatibility with pre- and post-processing tools, and easier coupling with related models. A large user community, extensive documentation, and companion software support make MODFLOW a central tool in groundwater modeling.