Head and elevation
For a connected point in a hydraulic model, pressure head depends on hydraulic head and ground elevation. Higher terrain can have insufficient pressure while lower terrain experiences excessive pressure within the same supply system.
A zone is also an operating arrangement
A GIS boundary helps organise customers and demand. It does not by itself control hydraulic connectivity. Identify the boundary valves, inlets, pressure controls and pumping arrangements that actually establish the supply zone. Keep the model and asset records aligned when a boundary changes.
Test interfaces and exceptions
- Verify normal valve statuses and possible emergency interconnections.
- Test zone inlet head over reservoir drawdown and changing demand.
- Check pressure-reducing valve behaviour and upstream availability.
- Review demand allocation around boundary properties and large customers.
Use combined models deliberately
Separate administrative supply zones may need one combined hydraulic model when transfer paths or shared assets influence performance. Preserve zone reporting so that balancing errors and service shortfalls remain visible. Read the hydraulic modelling guide before interpreting contour maps as evidence of compliance.
Use a hydraulic-grade profile
Plot ground elevation and hydraulic head along a supply route for relevant operating states. Their vertical difference gives pressure head at ordinary junctions. The profile makes it easier to distinguish terrain-driven low pressure from headloss along a constrained transfer route.
For an illustrative fixed-head source at 100 m, a node at 40 m with 5 m of cumulative headloss has 55 m pressure head. A node at 75 m with the same loss has only 20 m. Raising the source head helps the high point but also increases pressure at low points. The zoning decision therefore involves both ends of the elevation range.
Choose a zone boundary with operational meaning
A supply-zone polygon is a planning representation. The actual hydraulic boundary depends on valves, check valves, pressure-reducing valves, pumps and interconnections. Confirm which links are normally open, which can change state and which provide emergency transfer. A single model can represent several distinct zones when their interaction is part of the assessment.
Use asset records and operational evidence to explain each connection. An apparent overlap on a map may be a cartographic issue, while an unrecorded open valve can create a real hydraulic interaction. Resolve both before interpreting zone inflow or demand balance.
Pressure-reducing valves and booster pumps
A pressure-reducing valve dissipates available head to control a downstream condition within its operating capability. It cannot create head when upstream pressure is insufficient. Under some conditions it may become fully open and the downstream target will no longer be maintained. Check the valve state and upstream margin rather than assuming the setting is always achieved.
A booster adds energy but depends on inlet conditions, pump curves, control logic and power. Assess low-suction conditions, pump combinations, downstream maximum pressure and the response to shutdown. An added booster may move the problem upstream if the supplying main or reservoir is already constrained.
Separate normal, maximum and contingency states
| State | Why it matters |
|---|---|
| High demand, low source or tank level | Often relevant to minimum available pressure. |
| Low demand, high source level | Can govern maximum pressure in low-lying areas. |
| Valve bypass or alternate feed | Changes the hydraulic boundary and can affect both zones. |
| Pump trip or rapid valve event | May require transient assessment beyond an ordinary hydraulic run. |
Use current project requirements for acceptable service. Convert units explicitly: 1 m of water head is approximately 9.81 kPa at ordinary density. A pressure gauge reading, pipe elevation and terrain model can use different reference points, so verify the comparison basis.
Check zone changes against demand and quality
Rezoning moves demand between supply paths and may change flow direction, residual disinfection and storage turnover. Reconcile customer allocation before and after the change and simulate the full replenishment cycle. Check whether the newly supplying zone can sustain both its existing demand and the transferred load.
Retain boundary-valve states, operating instructions, telemetry changes and transition arrangements as part of the option. The GIS tutorial develops the customer membership comparison; the WS Pro guide connects that comparison to model demand and allocation.
Sources & further reading
- EPANET 2.2 User Manual ↗US Environmental Protection Agency · 2020
External source · Checked 24 September 2026
Source findings are distinguished from editorial interpretation. Apply current local criteria and project evidence when making engineering decisions.