EAM.4:5 - Archetypal Grounding
EAM.4:5.1 - Use a supplied requirement
In CityWater, North’s dry-window minimum is 700 m³/h and its wet-season minimum is 1,100. Current usable capability is 1,000. An annual average of 800 would not establish adequacy for the wet season: the explicit deficit is 100 m³/h at that required time. Both shortlisted C arrangements add 200 and pass this quantity comparison under their supplied qualifications.
Now suppose a new forecast suggests 1,250 in a later period. That forecast is not automatically a revised mandate. The practitioner reports that the current 1,200-capability option would fall short by 50 under this scenario and identifies which service or investment decision would use it. A sufficiently credible and consequential scenario can warrant another option without inventing a new commitment.
EAM.4:5.2 - Build the scenario from its components
In a separate constructed district, Westbank, compatible observations of an unrestricted critical hour give 1,000 m³/h at the inlet: 600 for households, 300 for other users and 100 losses. The case supplies compatible measurement coverage and the loss estimate. Proposed usable capability at the same inlet is 1,200 m³/h; required quality is unchanged.
| Component at the common critical hour | Observed base, m³/h | Scenario assumption | Scenario demand, m³/h |
|---|---|---|---|
| Household use | 600 | 10% more use on the same service basis | 660 |
| Other use | 300 | No material change | 300 |
| Losses | 100 | Qualified future estimate of 140 | 140 |
| Total at the inlet | 1,000 | Sum of compatible components | 1,100 |
The calculation is 600 × 1.10 + 300 + 140 = 1,100. It leaves 100 m³/h of contribution available within the proposed capability. A separately supported new industrial requirement of 150 during that same hour gives 1,250 and exceeds capability by 50. The industrial addition is counted once: it was absent from the 300 base.
If the industrial maximum occurs at another hour, the practitioner obtains the other components for that hour before forming its total. Adding unrelated maxima would not establish the actual peak. If the original 1,000 observation was rationed, the unrestricted baseline first needs an applicable estimate of suppressed use.
A proposed leakage measure may reduce the scenario’s losses from 140 to 80. With the industrial addition, the total would then be 660 + 300 + 150 + 80 = 1,190. EAM.7 can compare that measure with added supply, using its cost and evidence of achievable reduction. The ten-unit margin exists only while the assumed reduction, coincidence and other contributions remain supported. Treating the proposed 80 as the unchanged-policy loss estimate would hide the intervention that makes the option work.
These values illustrate the construction. They neither reconstruct CityWater’s supplied demand figures nor establish an empirical forecast for another district.