Flooding occus when the discharge of a river is so high that the river spills over its banks and onto the floodplain.
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How does prolonged rainfall cause flooding?
After a long period of rain, the ground becomes saturated and any further rainfall can infiltrate, which increase surface runoff, which increases discharge.
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How does heavy rainfall cause flooding?
This can lead to rapid surface runoff if the rainfall is too intense for infiltration to occur. This can lead to a sharp rise in river discharge, also known as a flash flood.
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How can melting snow and ice lead to a huge increase in a rivers discharge?
Melting snow, for example in the Himalayas, contributes to the annual summer flooding of the river Ganges in Bangladesh.
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What physical factors increase the risk of flooding?
Sparse vegetation, impermeable ground, circular drainage basins, high drainage density and Steep slopes.
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How does sparse vegetation increase the risk of flooding?
Sparse vegetation in the drainage basin means little rainfall is intercepted, so more rain reaches the ground. This increases the volume of water reaching the river, which increases discharge.
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How does impermeable ground increase the risk of flooding?
Clay soils and some rocks, such as granite and shale are impermeable. This means it doesnt allow infiltration of surface water. This increases surface runoff, which increases discharge.
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How do circular drainage basins increase the risk of flooding?
Water draining into the main river channel will all arrive in a short space of time because all points in the basin are similar distance from the river. This increases discharge.
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How does high drainage density increase the risk of flooding?
Drainage basins with a high drainage density drain quickly, so have a short lag time. Lots of water flows from the streams into the main river in a short space of time.
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How do steep slopes increase the risk of flooding?
If a drainage basin has steep-sided valley, water reaches the river channel much faster because it flows more quickly on a steeper slope.
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What human factors increase the risk of flooding?
Urbanisation, deforestation, flood management strategies, agriculture and climate change.
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How does urbanisation increase the risk of flooding?
Urban areas have large areas of impermeable tarmac and concrete, surface runoff is very rapid. Gutters and drains quickly take runoff to rivers. Both of these things reduce lag time, so therefore increase discharge.
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How does deforestation increase the risk of flooding?
Clearing trees and plants reduces interception and evapotranspiration. This increase the volume of water that reaches the channel, which increases discharge.
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How do flood management strategies increase the risk of flooding?
Some strategies can actually end up making flooding worse. if dams fail, they release a huge volume of water all at once, giving a huge increase in discharge.
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How does agriculture increase the risk of flooding?
Overgrazing leaves areas with less vegetation, so has the same effect as deforestation. Overgrazing and ploughing also increase soil erosion.
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How does climate change increase the risk of flooding?
Climate change could cause an increase in rainfall and more storms in some areas which could result in more flooding.
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How does flooding affect people?
People and animals can be killed. Contaminated flood water (disease). Damaged possessions. People can be made homeless. Lack of clean drinking water.
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How does flooding affect the economy?
Businesses shut down. Rescue work = costly. Unemployment levels rise. Public transport destroyed. Crops destroyed.
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How does flooding affect the environment?
Contaminated water pollutes rivers. River banks are eroded. Land becomes more fertile. Wetlands created -> home to rare species of animals.
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What type of floods dont happen often?
large magnitude floods dont happen as often as smaller floods.
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How can people predict how often a flood of a certain magnitude may occur?
Using the flood return interval (RI) - records are kept of floods, and looking back over them an estimate of the return interval (RI) can be estimated.
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What is the average return interval (RI) of a small flood?
RI = 1 - 3 years
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What is the average return interval (RI) of a large flood?
RI = 100years+
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Other cards in this set
Card 2
Front
When does flooding occur?
Back
Flooding occus when the discharge of a river is so high that the river spills over its banks and onto the floodplain.
Card 3
Front
How does prolonged rainfall cause flooding?
Back
Card 4
Front
How does heavy rainfall cause flooding?
Back
Card 5
Front
How can melting snow and ice lead to a huge increase in a rivers discharge?
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