The impact of human activities on flooding
Urbanisation
More people are living in towns and cities
Population growth + urbanisation= demand for land to build on - floodplains are flat and are food for housing
Concrete and tarmac = impermeable = preciptation cannot infiltrate = into the river much more quickly = reaches bank full discharge = floods
Less interception - trees and plant matter is removed = precipitation gets into the river much more quickly = reaches bank full discharge = floods
Surface water = channelled directly into drains and sewers = precipitation reaches the river much more quickly.
Bridges over rivers can constrict rivers, slow discharge and reduce the carrying capacity of the river.
Population growth + urbanisation= demand for land to build on - floodplains are flat and are food for housing
Concrete and tarmac = impermeable = preciptation cannot infiltrate = into the river much more quickly = reaches bank full discharge = floods
Less interception - trees and plant matter is removed = precipitation gets into the river much more quickly = reaches bank full discharge = floods
Surface water = channelled directly into drains and sewers = precipitation reaches the river much more quickly.
Bridges over rivers can constrict rivers, slow discharge and reduce the carrying capacity of the river.
Deforestation
In poor countries = rapid deforetation has taken place.
Land = used for framing, settlement and mining etc.
No trees = greater risk of soil erosion = the preciptation is not intercepted.
Flood damage = greatest near the mouth of a river - wide,flat floodplains = most susceptible to damage.
The volume of water is greatest here because many tributaires have joined the river.
Land = used for framing, settlement and mining etc.
No trees = greater risk of soil erosion = the preciptation is not intercepted.
Flood damage = greatest near the mouth of a river - wide,flat floodplains = most susceptible to damage.
The volume of water is greatest here because many tributaires have joined the river.
River Management
River management = reduce the likelihood of flooding.
However, in some circumstances it can actually increase the risk:
Bangladesh: flood embankments have built along some river channels = increase river capacity but at times have prevented floodwater draining back into the rivers
Farakka Dam, India: Lots of rainfall = lake behind the dam could burst = floodgates of the dam were opened = stopped the dam from bursting = increased the discharge of the river in Bangladesh.
This coincided with the normal floods and made the severity much worse
However, in some circumstances it can actually increase the risk:
Bangladesh: flood embankments have built along some river channels = increase river capacity but at times have prevented floodwater draining back into the rivers
Farakka Dam, India: Lots of rainfall = lake behind the dam could burst = floodgates of the dam were opened = stopped the dam from bursting = increased the discharge of the river in Bangladesh.
This coincided with the normal floods and made the severity much worse
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