EAM.6:5 - Archetypal Grounding

EAM.6:5.1 - A sufficient outage and buffer bound

CityWater’s North area has 1,000 m³/h usable capability before C is modified and needs 700 during the dry work window. Removing A’s 200 leaves 800; removing C’s 300 leaves 700. Each isolated outage passes the quantity bound. Removing both leaves 500, a 200 m³/h shortfall. Their individual feasibility therefore does not justify simultaneous work.

In an additional constructed variant, an independently qualified usable buffer contains 400 m³ and can cover that deficit at the required delivery conditions. The arithmetic gives 400 ÷ 200 = two hours. It cannot support a three-hour combined outage without another qualified contribution. This calculation assumes the stated usable volume and delivery rate; it does not derive them from tank size or establish water quality.

After the selected 200 m³/h addition, normal North capability is 1,200 against the wet minimum of 1,100. That comparison does not establish performance under every loss of station, power or control. Any such stronger claim needs its own applicable scenario or model.

EAM.6:5.2 - Shared failure and different recovery intervals

A separate constructed water system must continuously deliver 400 m³/h. Two units each supply a qualified 250 m³/h but share one feeder. An independent third source supplies 100 m³/h. Usable stored reserve is 300 m³, with delivery qualified for the deficits considered here. These are teaching inputs, not additional CityWater facts.

A feeder loss removes both 250 contributions. One returns after one hour and the other after two. During the first hour, only 100 m³/h remains, so preserving service requires (400 − 100) × 1 = 300 m³. The reserve is exhausted at one hour. During the next hour, 250 + 100 = 350 m³/h leaves another 50 m³/h deficit. The arrangement fails the continuous-service requirement despite normal capability of 600 m³/h.

Now consider a qualified additional 250 m³/h supply that can operate independently of this feeder loss and is usable after half an hour. Its support and connection are supplied as case premises.

Before the first feeder-dependent unit returns, required reserve is 150 + 25 = 175 m³. The initial 300 therefore covers the stated intervals, leaving 125 m³; no replenishment is assumed. From one hour, the available contributions meet the 400 requirement. The added supply is a feasible response to this constructed scenario, to be compared with other supported remedies and their burden.

If the added supply actually depends on the failed feeder, remove its contribution and the first conclusion returns: service fails after one hour. If it is independent but becomes usable only after 1.5 hours, the first hour exhausts storage and the next half-hour has a 50 m³/h deficit. Independence alone therefore does not establish timely service. Earlier availability, a further usable 25 m³ of reserve, a different restoration arrangement or another supported alternative could change that latter result.

Use actual dependency and restoration evidence before relying on such a calculation. The case establishes neither the probability of feeder loss nor the hydraulic feasibility of an unexamined network. EAM.7/.8 compare the supported remedy; EAM.11 must retain its half-hour availability and restoration conditions in the time arrangement.