Reading: Diagram Label Completion: Question 1

A canal that crosses hilly or uneven ground cannot simply be dug at a single level, since water will not stay in a channel that slopes continuously downhill. Engineers solve this problem with a device called a pound lock, a mechanism that lifts or lowers boats between two stretches of canal, known as pounds, that sit at different heights.

A pound lock consists of a rectangular chamber built between two sets of watertight gates. At the upstream end, where the chamber meets the higher pound, stand the upper gates; at the downstream end, where it meets the lower pound, stand the lower gates. Each gate is a heavy timber or steel structure hinged at one edge and closes against a stone ledge, called the cill, set into the floor of the chamber; the cill prevents water from forcing the gates open from the wrong side. Fixed to the top of each gate is a long wooden balance beam, which projects out over the towpath; a lock keeper, or on quieter canals a boater, pushes against this beam to swing the heavy gate open or shut, since the beam's length provides enough leverage for one person to move it.

Built into the lower part of each gate is a small sliding panel called a paddle. Raising a paddle in the upper gates allows water to flow from the upper pound into the chamber, gradually raising the water level inside until it matches the upper pound; only then can the upper gates be opened safely, since gates can never be opened while there is a difference in water level across them. To lower a boat, the process is reversed: with both gates shut, the paddles in the lower gates are raised instead, draining water out of the chamber into the lower pound until the level inside falls to match it, at which point the lower gates can be swung open and the boat continues on its way.

The diagram below shows a lengthwise cross-section of a pound lock, running from a higher stretch of canal on the left to a lower stretch of canal on the right, with the chamber in between.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the stretch of open water at the higher level, to the left of the lock
2. the gates at the left-hand (upstream) end of the chamber
3. the ledge set into the floor of the chamber that each gate closes against
4. the long wooden arm fixed to the top of each gate, used to push it open
5. the small sliding panel built into the lower part of each gate
6. the enclosed section of water between the two sets of gates
7. the stretch of open water at the lower level, to the right of the lock