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Site-scale watershed modeling

Single-catchment models at 30-meter resolution

A single-catchment SWAT+ model — optionally coupled to MODFLOW 6 — rebuilt at 30 m and nested inside a HUC12 watershed model that hands it boundary conditions.

  • HUC14 · single catchment
  • 30 m grid
  • SWAT+ (+ optional MODFLOW 6)
  • Nested in a HUC12 model
Site-scale model output at Wurtsmith AFB, Michigan: a simulated 30 m PFOS plume on aerial imagery, with AFFF source zones and the monitoring-well network.

Most of what SWATGenX builds is basin-scale: a complete SWAT+ model for a HUC12 watershed, optionally coupled to a 3-D MODFLOW 6 aquifer. Site-scale modeling turns that same automated pipeline on a much smaller target — one HUC14 catchment — and rebuilds it at 30 m so the grid is fine exactly where a site investigation needs it.

The two models are nested, not independent. The HUC12 model resolves regional flow and supplies the site model its inflow and groundwater boundary conditions; the HUC14 model spends its resolution on the plume, the wellfield, and the vadose zone. It is the same platform-generated, expert-finished workflow — assembled from national datasets, then reviewed by a modeler — applied at a scale where every cell counts.

Why a nested site model

HUC12 is too coarse for a site
A production HUC12 model resolves a basin at ~250 m — right for regional water balance and streamflow, but a single contaminated catchment, a wellfield, or an AFFF source area is only a few cells wide.
The vadose zone needs fine cells
Where a plume descends through a shallow sandy unsaturated zone, explicit vertical transport — not a screening shortcut — changes the answer. That resolution has to exist in the grid.
Site studies are catchment-sized
Monitoring networks, permit boundaries, and source zones sit inside one or two HUC14 catchments. Modeling exactly that footprint keeps the grid fine where the data are.

How it is ordered

You do not assemble anything by hand. In the Watershed Explorer you pick a point, generate the HUC12 watershed model, then drill in and select the HUC14 catchment to rebuild at 30 m — the watershed run becomes the site model's boundary.

1
Pick a point
anywhere in CONUS, in the Watershed Explorer
2
Watershed model
HUC12 · SWAT+ (+ optional MODFLOW 6) · ~250 m
3
Site model
HUC14 · single catchment · nested · 30 m
4
Boundary hand-off
the HUC12 run supplies inflow + groundwater context

Worked examples

The exemplars below are contaminant-transport site models built on the nested pattern. Both put land-surface loading, vadose-zone descent, and aquifer transport into one MODFLOW 6 simulation at 30 m.

Wurtsmith AFB, Oscoda MI
A 77 km² observation-anchored HUC14 footprint rebuilt at 30 m inside the 732 km² Van Etten Lake–Pine River watershed model, with explicit UZF/UZT vadose transport carrying PFAS from an AFFF source term down to a plume validated against a 35-well network.
Gabreski ANGB, Long Island NY
A companion coastal-aquifer site model on the same nested pattern — a second point on the vadose-zone spectrum, chosen to stress the workflow where the water table is shallow and the flow field is flat.

The Wurtsmith build is documented end to end — nested workflow, vadose transport, and an interactive 3D plume — on the watershed-to-site PFAS page.

Start a site model

Model generation is free with an account; you only reach for paid cloud calibration if and when you want it. Contaminant, vadose-zone, and site-investigation studies that need finer than a basin-scale model start here.

Page updated 2026-07-13. Platform-generated, expert-finished.