1Fort Custer Aquifer Water Balance
Step 1 — Load Parent Model and Create Submodel
Click 
to load the regional model from Tutorial 1. Click 
to simulate, then add a submodel and apply 'Boundary Conditions from Parent Model' in the Default Model Input Parameters and Display Options Menu.
Step 2 — Add a River (Prescribed Head Boundary)
Click 
the 'DrawLine' and 'SaveShape' buttons to add a polyline feature along the Kalamazoo River. Assign this as a prescribed head boundary condition — the river stage is fixed, and the aquifer exchanges water with it depending on the head difference.
Step 3 — Add a Wetland Drain (One-Way Head-Dependent)
Click 
the 'ZonePoly' and 'SaveShape' buttons to add a wetland zone near the Kalamazoo River. Assign this as a one-way head-dependent boundary condition (drain) — water can only leave the aquifer through the drain when the water table is above the drain elevation. Water cannot enter the aquifer from the drain.
Step 4 — Add a Lake (Two-Way Head-Dependent)
Click the 'ZonePoly' button to add a lake zone on the east side of the Fort Custer area. Assign this as a two-way head-dependent boundary condition — the lake can both gain water from the aquifer (when water table is above lake level) and lose water to the aquifer (when lake level is above water table).
Step 5 — Add a Pumping Well
Click 
the 'Well' button to add a pumping well to the model domain. The well appears as a yellow dot on the map. Set the pumping rate in the well properties dialog.
Step 6 — Submit for Simulation
Click 
to submit the model for simulation. The solver computes the flow field with all boundary conditions active — river, drain, lake, recharge, and pumping well all interacting simultaneously.
Step 7 — View the Mass Balance Chart
Click 
the 'Analysis' button, then select 
'Display Charts' from the submenu. This launches analysis windows including the Mass Balance Bar Chart — showing every inflow and outflow component: recharge, river exchange, lake exchange, drain discharge, well pumping, and boundary fluxes. The chart quantifies exactly where water comes from and where it goes.
Step 8 — Save or Publish
Click 
to save or publish the model for future use.
Key Concepts
Three types of head-dependent boundaries: Prescribed head (river — fixed stage, bidirectional flow), two-way head-dependent (lake — exchange depends on head difference, bidirectional), and one-way head-dependent (drain — water can only leave the aquifer, not enter). Each type has different physics and different impacts on the water balance.
The mass balance chart is automatic: Every boundary condition you add to the model is automatically reflected in the mass balance chart. No manual setup needed — the chart reads directly from the solver output. Add a feature → simulate → see its contribution to the budget immediately.
Mass balance as quality control: A large mass balance error (inflows ≠ outflows) indicates a numerical problem — the grid may be too coarse, the solver may not have converged, or a boundary condition may be poorly configured. Always check the mass balance before interpreting results.
2What's Next
With water balance analysis mastered, continue the learning path:
Tutorial 5: Contaminant Transport — add solute sources and simulate plume migration through the flow field you've built
Tutorial 6: Vertical Details — extend to 3D with multiple layers and confining units
Tutorial 7: Transient Modeling — add time-varying pumping, seasonal recharge, and dynamic water levels