GSFLOW — The Complete Guide: Coupled Surface-Water and Groundwater Modelling for Whole Basins
GSFLOW from the USGS joins two established models: PRMS, which simulates watershed surface hydrology (runoff, infiltration, evapotranspiration), and MODFLOW, which simulates groundwater flow. The result is a single water budget for the whole basin. It is in the public domain, with source code and ready-to-run packages for Windows and Linux.
GSFLOW
U.S. Geological Survey (USGS)
Coupled groundwater and surface-water model for whole watersheds, linking PRMS with MODFLOW.
Get it from the vendorWhat you get
- Full coupling — surface water and groundwater computed together in one run.
- Stream–aquifer exchange — gains and losses between streams, lakes and groundwater.
- Soil zone — infiltration, evapotranspiration and recharge.
- Scenarios — the effect of pumping, land use and climate on streamflow.
- Basin water budget — a full breakdown of budget components over time.
What to keep in mind
There is no graphical interface of its own: input files are prepared in a text editor or with ModelMuse, and you need to know both underlying models. Check the USGS page for the currently recommended version — USGS reports two bugs in soil-zone calculations in version 2.3.0 and recommends 2.2.1. It suits hydrologists and water-resources engineers.
Related tools
For a groundwater-only model — MODFLOW 6. For an agricultural catchment model with water quality — SWAT. For building the model grid — ModelMuse.
PRMS
U.S. Geological Survey (USGS)
Watershed hydrology model: from precipitation to runoff, infiltration and streamflow.
Get it from the vendorMODFLOW 6
U.S. Geological Survey (USGS)
The world standard for groundwater flow and solute transport modelling, from the USGS.
Get it from the vendorSWAT
Texas A&M AgriLife / USDA-ARS
A watershed model — runoff, erosion, nutrients and pesticides over decades.
Get it from the vendorModelMuse
U.S. Geological Survey (USGS)
The free graphical interface to MODFLOW — build the model with a mouse instead of text files.
Get it from the vendorThe bottom line
When the link between streams and groundwater is the heart of the problem, GSFLOW is one of the strongest free tools available — at the cost of a steep learning curve.