Site-scale watershed modeling
HUC14 catchment models nested in the watershed
A single-catchment SWAT+ model — optionally coupled to MODFLOW 6 — nested inside a HUC12 watershed model that hands it boundary conditions. Built for long-run contamination and plume studies at site scale.
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 — so the study footprint sits on the drainage area that holds the site, the plume, and the monitoring network.
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 carries the catchment-scale story for 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 where site investigations actually live.
Why a nested site model
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 nest as the site model — the watershed run becomes the site model's boundary.
Open the Watershed Explorer to start, or read how models are built.
Worked examples
The exemplars below are contaminant-transport site models built on the nested HUC14 pattern. Both put land-surface loading, vadose-zone descent, and aquifer transport into one coupled MODFLOW 6 simulation at catchment scale.
The Wurtsmith build is documented end to end — nested workflow, vadose transport, and an interactive 3D plume — on the watershed-to-site PFAS page.
PFAS at site scale
The most common reason to build a nested site model is contaminant fate and transport — and PFAS is the flagship case. The same HUC14 site build carries a PFAS source term through the vadose zone and into a MODFLOW 6 / GWT aquifer with Freundlich sorption, while the HUC12 model supplies the regional flow field. The advantage over a hand-built desktop model is the data: the National PFAS Soil Inventory (30,972 depth-resolved records) seeds the source term and the groundwater lithology inventory supplies aquifer geometry automatically, so the site model has a defensible starting point before you add local boring or monitoring data.
The full mechanism story — sorption, air–water interfacial retardation in the vadose zone, plume growth, and groundwater discharge to streams, with an honest comparison to HYDRUS, MODFLOW/MT3DMS+GMS, and dedicated PFAS tools — is on the PFAS fate-and-transport page, and the nested Wurtsmith build is documented method-by-method 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.
FAQ
What is site-scale (HUC14) watershed modeling on SWATGenX?
A single-catchment SWAT+ model — optionally coupled to MODFLOW 6 — built for one HUC14 catchment and nested inside a coarser HUC12 watershed model that supplies its boundary conditions. It exists for contaminant fate-and-transport, vadose-zone, and site-investigation studies that need catchment-scale context a basin-scale model alone cannot resolve.
Why build a HUC14 site model instead of using the HUC12 watershed model?
A HUC12 model resolves a basin at about 250 m — right for regional water balance and streamflow, but a single contaminated catchment, wellfield, or source area is only a few cells wide at that resolution. Nesting a HUC14 site model keeps the study footprint on the catchment that holds the plume, the monitoring wells, and the vadose zone, while the HUC12 model still supplies inflow and groundwater context.
How do I simulate PFAS fate and transport at my site?
Generate the HUC12 watershed model over your area in the Watershed Explorer, then drill in and rebuild the single HUC14 catchment around your site, coupled to MODFLOW 6 for three-dimensional groundwater transport. The watershed model supplies the site model’s inflow and groundwater boundary conditions, while the National PFAS Soil Inventory and the groundwater lithology inventory populate the source term and aquifer automatically; site-specific boring and monitoring data then refine it. The mechanisms and a worked Wurtsmith example are documented on the PFAS fate-and-transport and watershed-to-site PFAS pages.