SWAT+MODFLOW-6 | SWATGenX
Surface water and groundwater in one order: SWATGenX builds the SWAT+ watershed model, then automatically builds and links the steady-state MODFLOW 6 groundwater model beneath it — grounded in real driller-log well records.
What a SWAT+MODFLOW-6 order gives you
A single order, one pipeline, two linked models. The SWAT+ model simulates land processes and streams; its simulated percolation becomes the recharge field of a MODFLOW 6 model whose layer geometry, hydraulic conductivity, and starting heads are kriged from real water-well records. The groundwater build starts automatically the moment the SWAT+ build succeeds — you never order the two halves separately, because the groundwater model cannot exist without the SWAT+ model it is built from.
The current product scope is steady-state MODFLOW 6 — the long-term water-table configuration consistent with the SWAT+ water balance, validated against observed static water levels at wells. Transient groundwater modeling is deliberately out of scope. The same open engine also supports live daily two-way coupling (SWAT+ percolation → MODFLOW recharge; MODFLOW stream leakage → SWAT+ channels) for research use.
Availability: groundwater builds are currently offered for watersheds in the Michigan Lower Peninsula, where the statewide well database provides the hydrogeologic layers. The SWAT+-only model type is available across CONUS.
Demonstration — hydrology, end to end
South Ore Creek (Huron River headwaters, Michigan) — HUC12 041000130111 — built with the standard pipeline (no manual tuning), then head-calibrated and validated from the Calibration page. All numbers below are reproducible from the public workflow.
| Stage | Head NSE | KGE | RMSE (m) | Observation wells |
|---|---|---|---|---|
| As built (uncalibrated) | 0.47 | 0.72 | 7 | 872 |
| Calibrated (7-parameter DE) | 0.59 cal / 0.48 validation* | 0.74 | 5.6 | 872 |
*Calibration–validation split: a random 30% of the observation wells is held out of the optimization entirely and scored separately — every calibration is a validation experiment. Sensitivity screening (one-at-a-time around the calibrated optimum) ranks the head-controlling parameters: lower-drift horizontal conductivity dominates, recharge is second, and vertical conductivities and river conductance are negligible at steady state.
The scientific basis of the coupling — the two-way SWAT+/MODFLOW 6 exchange — is described in our methods manuscript, currently under peer review: “Watershed-scale PFAS fate and transport across surface water and groundwater: a two-way coupled SWAT+/MODFLOW 6 model quantifies the legacy groundwater contribution to in-stream loads”. The demonstration above is a separate, hydrology-only model: none of the publication models are reused here.
The coupled engine is open
The engine that runs SWAT+MODFLOW-6 — SWAT+ with the MODFLOW 6 coupling, HRU-parallel execution, and NetCDF output — is open source. If you prefer to run or calibrate the coupled model yourself rather than through SWATGenX, download your model package and compile the engine:
github.com/rafiei-vahid/swatplus
The repository builds on Linux and Windows (Intel Fortran recommended) and runs any SWATGenX model package. MODFLOW 6 itself is the USGS release, loaded as a library.
How to get one
1. Open the Watershed Explorer and pick a Michigan Lower Peninsula watershed (USGS station, catalog HUC12, or HUC8).
2. Click Create SWAT+ Model and choose the SWAT+MODFLOW-6 model type in the request dialog — the groundwater build chains automatically after SWAT+.
3. Watch both builds live on your Dashboard (MODFLOW tab), download either model, and run head calibration–validation when the build converges.