Reading: Diagram Label Completion: Question 6

Run-of-river hydroelectric schemes generate electricity by diverting a portion of a river's natural flow through a low, compact dam, rather than storing enormous volumes of water behind a high one. The scheme built across the Kestrel River in 2021 by the regional utility Marrowvale Power illustrates the basic arrangement shared by most such dams.

At the upstream end of the structure, a concrete spillway allows excess floodwater to pass safely over the crest of the dam whenever the reservoir behind it rises above its normal operating level, preventing the structure from being overtopped in an uncontrolled way. Immediately beside the spillway, water destined for power generation first passes through a trash rack, a steel grille of closely spaced bars that stops branches, leaves and other floating debris from reaching the machinery further downstream. Water that clears the trash rack enters an intake channel, a short, gently sloping passage cut into the dam that funnels the flow toward the generating equipment and gradually narrows to increase its speed.

From the base of the intake channel the water is forced into a penstock, a large steel pipe that carries it under considerable pressure down to the turbine hall at the foot of the dam. Engineers at Marrowvale Power chose a steel penstock over a concrete one because steel tolerates the sudden pressure surges that occur whenever the flow is throttled quickly. Inside the turbine hall, the pressurised water strikes the curved blades of a turbine, spinning a shaft connected to a generator on the floor above; the turbine's rotational energy is converted into electrical energy at this point, and cables carry the output to a substation on the riverbank.

Having passed through the turbine, the water is not stored again but is released into a tailrace, a wide open channel that returns it to the natural riverbed a short distance downstream of the dam. Because the dam interrupts the river's natural course, a fish ladder, a stepped series of pools running alongside the main structure, allows migratory fish such as salmon to bypass the dam and continue upstream to their spawning grounds, a feature required by Marrowvale Power's environmental operating licence.

The diagram below shows a cross-section of the Kestrel Gorge dam, viewed from upstream to downstream (left to right). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The structure at the top of the dam that lets floodwater pass over the crest when the reservoir is too full 2 ____________________. A steel grille positioned beside it that stops debris before it can reach the generating equipment 3 ____________________. The narrowing passage that funnels water from the grille toward the generating equipment 4 ____________________. The large steel pipe that carries pressurised water down to the turbine hall 5 ____________________. The part inside the turbine hall struck directly by the pressurised water, turning the connected generator shaft 6 ____________________. The open channel that returns water to the riverbed after it leaves the generating equipment 7 ____________________. The stepped series of pools beside the dam that lets migratory fish continue upstream