Why does flooding occur?
A flood occurs when a river bursts its banks and the water spills onto the An area around a river that is covered in times of flood. Alluvium (silt) is deposited when floodwater covers the area. .
The causes of Floods will happen when there is a temporary increase in the amount of water in the river. The water will overflow from the river channel onto the surrounding land (flood plain). are usually a result of both physical and human factors.
Physical factors
Climate
Flooding is caused by heavy rainfall. The faster the rainwater reaches the The part of the river that holds the water., the more likely it is to flood. The nature of the landscape around a river will influence how quickly rainwater reaches the channel.
A steep-sided channel
A river channel, surrounded by steep slopes, causes fast Water moves across the surface of the earth becoming a stream, tributary or river (transfer)..
A lack of vegetation/woodland
Trees and plants intercept precipitation, ie they catch or drink water. If there is little vegetation in the drainage basin then surface run-off will be high.
Impermeable rock
A The area of land that is drained by a river and all its tributaries., consisting of mainly Rock type in which water cannot pass through. rock will mean that water cannot percolate through the rock layer, and so will run faster over the surface.
Human factors
Drainage basins in urban areas
A drainage basin in an urban area consists largely of impermeable rock and concrete, which encourages overland flow. Drains and sewers take water quickly and directly to the river channel. Houses with sloping roofs further increase the amount of overland flow.
Deforestation
In areas where trees and forests have been purposely cut down and destroyed by humans, flood risk dramatically increases. This is because trees intercept and absorb water as part of photosynthesis. Without trees, rainfall directly hits the surface and may quickly saturate soils or run-off into nearby rivers, causing the rivers to rise quickly.