Flooding in drainage basins
Flooding is a major issue in drainage basins in Wales, the UK and around the world. This section will explore what a drainage basin is, what processes operate in a drainage basin and why flooding occurs. It will also look at the effects of flooding in one UK location, and what can be done to manage and reduce the threat of future flooding.
Managing flooding
River management
Steps can be taken to manage flooding. This is known as river management. Often these steps involve trying to lengthen the amount of time it takes for water to reach the river channel, thereby increasing the lag time.
Hard engineering methods tend to be more expensive and have a greater impact on the river and the surrounding landscape. They will require more extensive alterations to the river to try to stop flooding.
Soft engineering methods are usually more ecologically sensitive. They will attempt to manage flood rather than prevent it.
Hard-engineering
Dams
- Built along the course of a river to control the amount of discharge. Water is held back by the dam and released in a controlled way.
- Water is usually stored in a reservoir behind the dam. This water can then be used to generate hydroelectric power or for recreation purposes.
- Expensive to build.
- Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.
Flood walls
- Can be used to raise the height of the river bank to a level where the river might not burst its banks.
- Can be permanent features or incorporated into the design of an area and become invisible.
- Can also be temporary structures where flood gates or removable ‘stoplogs’ are built to protect a stretch of river.
Levees and embankments
- Artificial levees can be built along river banks so that if the river floods, the water will not be able to breach the wall and cause damage. Levees can be expensive and can spoil the look of rivers.
- Flood embankments are usually used in rural areas. They can take up a lot of space and are cheaper than flood walls but they can also cause the speed of the water in the river to be increased which will just move any potential flooding further downstream.
River engineering
- The river channel may be widened or deepened allowing it to carry more water. A river channel may be straightened so that water can travel faster along the course. The channel course of the river can also be altered, diverting floodwaters away from settlements.
- Altering the river channel may lead to a greater risk of flooding downstream, as the water is carried there faster.