Define the service problem
Identify where, when and under what operating conditions the network falls short. Distinguish a demand-driven pressure deficit from a closed valve, incorrect model elevation, constrained source head or control issue. An apparent pipe capacity problem may have a different root cause.
Build an assessment matrix
- Existing and future demands, including sensitivity to the timing and location of development.
- Normal operations and credible asset outages with realistic isolation boundaries.
- Relevant tank levels, source availability and pump duty combinations.
- Pressure, transfer capability, replenishment, water age and operational flexibility.
Compare coordinated options
Candidate responses include demand management, a revised pressure zone, control changes, a parallel or upgraded main, booster pumping and additional storage. Evaluate the whole operating cycle. A pump may improve local pressure while increasing upstream demand or changing reservoir drawdown.
Stage the investment
Link delivery to observable triggers such as connected dwellings, measured peak flow or a verified service shortfall. Include lead times, land, power and construction dependencies. Adaptive investment planning can preserve flexibility where growth is uncertain.
Define scenarios that represent real operating states
A scenario combines demand, source levels, available assets, controls and the assessment period. A peak-demand case with every reservoir fixed at its highest level can be less demanding than the actual operating cycle. Conversely, combining every worst value without considering whether the combination is credible can produce an unrealistic design requirement.
Build the matrix with operations staff and document why each combination matters. Separate normal service, planned maintenance, credible failure and emergency conditions. Apply the corresponding accepted criteria and response expectations, rather than assuming all scenarios require the same service outcome.
Find the bottleneck through a sequence of checks
- Confirm that the low-pressure result is not caused by an elevation, unit, demand or topology error.
- Trace the hydraulic-grade profile from the source to affected customers during the governing time.
- Identify where head is consumed and whether the constraint changes as storage falls or pumps switch.
- Check whether the upstream system can sustain the added transfer that a local upgrade would require.
- Test the candidate intervention alone, then assess its interaction with the full operating cycle.
A pipe with high velocity is a diagnostic clue, not an automatic instruction to increase diameter. Its loss, duration, criticality and interaction with the rest of the system matter. Apply project criteria in context and retain the evidence supporting the chosen intervention.
Understand why parallel paths do not simply double capacity
For two pipes between common end nodes, headloss across each path must be equal while the total flow is shared. Flow does not necessarily split equally when lengths, diameters, roughness or fittings differ. A new parallel main can also move the upstream pump operating point and change flows elsewhere.
In an isolated system with identical parallel pipes and fixed available head, the total flow can approach twice the single-pipe flow under the same resistance assumptions. In a real connected system, source, pump, treatment or downstream constraints may prevent that gain. Quantify the system response rather than assigning a generic capacity multiplier.
Compare options beyond the passing simulation
| Dimension | Questions for the option assessment |
|---|---|
| Service | Does it resolve the defined failures across relevant scenarios and future stages? |
| Operations | Can controls, isolation and maintenance be managed with available staff and assets? |
| Constructability | Are corridors, crossings, land, power and shutdown windows feasible? |
| Whole-of-life performance | What are capital, energy, maintenance, renewal and residual risks? |
| Water quality | Does the option alter residence time, blending, residual or turnover? |
Use a common comparison boundary and price basis. Keep uncertainties visible and test whether they change the ranking. A staged option can be attractive when growth timing is uncertain, provided an observable trigger and a feasible delivery lead time are established.
Write a result that can be reviewed
State the governing scenario, affected assets, duration and physical mechanism. Describe which model evidence was checked and the criteria applied. Explain how the selected option changes the mechanism and what residual dependencies remain.
A statement such as “the model passes” is incomplete without those conditions. Connect the findings to investment staging and the augmentation framework.
Sources & further reading
- EPANET 2.2 User Manual ↗US Environmental Protection Agency · 2020
External source · Checked 24 September 2026 - Best Practice Modelling Guidelines ↗eWater · 2011
External source · Checked 24 September 2026
Source findings are distinguished from editorial interpretation. Apply current local criteria and project evidence when making engineering decisions.