Rivers - Controlling

1. Many rivers and canals have locks to make them navigable.

2. Locks are necessary when the water level changes between one section of the river and another.

3. Locks are deep tanks of water, large enough to hold a river boat, with a set of gates at each end.

4. Lock gates work in pairs to control the flow of water into, and out of, locks.

5. When the gates are closed they create a watertight seal, preventing water entering or leaving the lock.

6. When the gates are open they allow the water to flow freely in and out.

7. Locks allow boats to travel between higher and lower water levels.

8. If the top gate is open and the bottom one closed water will pour into the lock.

9. If the top gate is closed and the bottom one open, water will pour out of the lock into the river.

10. A weir is a dam built across a river or stream to control the flow of the river water.

11. It is usually built to make a river navigable.

12. By creating a weir, the flow of the water upstream is slowed, and the depth of the water increased.

13. A sluice is a water channel controlled by gates used to control the depth and flow of water in a river.

14. Sluices and weirs often have walkways over the top to enable workers to remove debris which collects in them.

15. Heavy gates are lowered or raised in order to control the water.

16. When the gates are fully lowered, they prevent the water flowing through.

17. If they are raised, they allow the water to flow underneath

18. Dams are walls of earth, concrete or rock.

19. They are built to retain water, control floods, supply water, improve navigation and provide electric power.

20. An artificial lake, or reservoir, often forms behind the dam which can be used for water, or for recreational activities.

21. Flood plains are a river’s natural defence mechanism to provide relief and take up excess water.

22. Floodplains are areas of flat land around river channels.

23. They are formed during times of flood when the amount of water is greater than the river can hold.

24. The floodplain becomes covered with water and mud, known as alluvium, is left behind when the floodwaters go away.