River Flooding & Man
Why do rivers flood?
Floods are natural events. They mainly happen when the river catchment, (that is the area of land that feeds water into the river and the streams that flow into the main river) receives greater than usual amounts of water (for example through rainfall or melting snow). The river cannot cope and this extra water causes the level of the water in the river to rise and a flood to take place. This flooding may take place at any point along the river course and not necessarily at the place where the extra water has entered.
In 1947 a severe winter blew into Europe from Russia. "When it began to thaw the River Trent burst its banks and brought floods to Nottingham. Fifty thousands acres of farmland were engulfed by water with hundreds of homes cut off from dry land. Two and a half thousand acres of the city were waterlogged, submerging 28 miles (45 km) of streets."
Although man often seeks to protect himself and his property from the often-damaging effect of floods, man can use them to his advantage.
The people of Egypt used the regular event of the River Nile flood to their advantage. Until 1970, the Nile had flooded every Spring as the mountain snows melted. This flooding of the flat land (floodplains) alongside the river enriched the soils leaving behind rich silt in which crops could be grown.
The construction of the Aswan Dam in the 1960's meant that from 1970 the annual flood was controlled - many people do not agree with interfering with nature!
Man has long tried, not always successfully, to control and prevent the damaging effects of flooding rivers. River engineers may build artificial flood banks, straighten the river course, or dredge the riverbed to make it deeper. All of these methods of control can work, although they often have a negative effect on the river as a habitat.
The Environment Agency has a major role in the control of river flooding and the protection of people and their property. Their job is a difficult one has there is an increasing tendency of rivers towards 'flash flooding' - this is where rainfall or melting ice and snow result in a rivers level rising extremely quickly, often far more quickly than in past years.
Thames Barrier the world's largest movable flood barrier, spans 520 metres (a third of a mile) across the Thames at Woolwich Reach, South East London, where it protects the UK's capital city from flooding.
Answer the following:
1 Briefly describe what causes a river to flood.
2 Describe how man can use a flood to their advantage.
3 Describe the different ways in which we can control the flow of a river.