1Fort Custer Model Hierarchy
Step 1 — Load and Simulate the Parent Model
Click 
to load the parent model from Tutorial 1 and submit for simulation. This establishes the regional flow solution that provides boundary conditions for the submodel areas.
Step 2 — Draw the First Submodel Zone
Click 
the 'ZoneRect' tool to draw a rectangular zone within the parent model, representing a subregional area of interest. Click 'SaveShape' to open the Zone Attributes menu.
Step 3 — Activate as Submodel Domain
In the Zone Attributes menu (Flow Property tab), check the box next to 'Submodel Domain' and select the 'Active' option. This tells IGW-NET to use this zone as the computational domain for the next simulation — the grid will be generated within this zone, at finer resolution than the parent, while boundary conditions are extracted from the parent solution.
Step 4 — Create a Nested Site Zone Inside
Create another, smaller zone feature inside the first submodel zone — this represents the site-level area of interest. Check 'Submodel Domain' in its Zone Attributes, but this time select 'Polygon Only'. "Polygon Only" means the zone exists as a defined area but is not yet the active computational domain — it's queued for later use.
Step 5 — Simulate the Subregional Model
Click 
— in the Domain Attributes menu, apply 'Boundary Condition from Parent Model'. Submit for simulation. The solver runs within the larger (Active) submodel zone, producing a finer-resolution solution for the subregional area.
Step 6 — Switch: Deactivate the Subregional Zone
Click 
the 'Geometry unlocked' or 'ZoneAttr' tool to open the Zone Attributes of the larger submodel zone. Change its Zone Type from 'Active' to 'Polygon Only'. This deactivates it as the computational domain while keeping it visible in the model.
Step 7 — Activate the Site Zone
Open the Zone Attributes of the smaller (site-level) zone. Change its Zone Type from 'Polygon Only' to 'Active'. Save changes and apply 'Boundary Condition from Parent Model' in the Domain Attributes menu. Now the site zone becomes the computational domain.
Step 8 — Simulate the Site Model
Submit for simulation. The solver now runs within the smaller site zone at even finer resolution — boundary conditions inherited from the subregional solution. You've zoomed from regional → subregional → site, all within one model file.
Active vs Polygon Only
Active: This zone IS the computational domain. The grid is generated within it, the solver runs within it, and results are produced for it. Only one submodel zone can be Active at a time.
Polygon Only: The zone exists as a drawn feature — visible on the map, stored in the model file — but it's not being used as the computational domain. It's a placeholder that you can activate later. Think of it as a "bookmark" for an area of interest.
The workflow is: draw all your zones of interest upfront, set one to Active, simulate, review results. Then switch Active/Polygon Only status and simulate the next area. All zones, all scales, one model.
When to Use Zone-Based vs Nested Modeling
Use nested modeling (Tutorial 2) when: You want clean separation between parent and child. Each model is an independent file. Simple, straightforward, good for single-site studies where you're zooming into one area.
Use zone-based hierarchy (this tutorial) when: You're managing multiple areas of interest within one region. You want to switch between scales without loading different files. You want all your features and zones visible simultaneously. Good for multi-site projects, teaching scenarios where you demonstrate different zoom levels, or collaborative environments where different team members work on different zones.
2What's Next
With zone-based hierarchy mastered, continue the learning path:
Tutorial 12: Profile Modeling — view and analyze flow in cross-section
Tutorial 13: Importing Shapefiles — bring external GIS data into your hierarchical model
Tutorial 14: Post-Analysis Tool — load and inspect completed models across your hierarchy