AQA AS Geography Rivers: Flooding and Flood Management

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  • Created on: 22-08-13 20:13
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Causes of Flooding
Flooding occurs when the discharge of a river is so high that the river spills over its banks
onto the flood plain.
There are three different contributors to flooding:
Natural causes
Physical factors
Human factors
Natural Causes
Natural causes of river flooding may be classified as follows:
Primary Causes Usually the result of climatic factors e.g. heavy rainfall
Secondary Causes Drainage base specific
Natural causes of flooding
Prolonged rainfall After a long period of rain, the ground
becomes saturated
Any further rainfall can't infiltrate, which
increases surface runoff, which increases
Heavy rainfall Leads to rapid surface runoff if the rainfall is
too intense for infiltration to occur
This can lead to a sharp rise in river
discharge called a flash flood
Melting snow and ice Increase river discharge quickly

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Physical Factors
Sparse vegetation Means little rainfall is intercepted so more
water reaches the ground
Increases the river discharge
Deciduous trees Have no leaves in the winter
Little rainfall is intercepted
Impermeable ground Clay soils and some rocks, such as granite
and shale, are impermeable ­ they don't
allow infiltration of surface water
This increase surface runoff, which increases
If the ground has been baked hard by the
heat of the summer, or it's frozen ­ water
can't infiltrate, increasing surface runoff and
discharge…read more

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Human Factors
Human factors often make flooding more frequent and more severe by changing things in
the drainage basin.…read more

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Impacts of Flooding
Social Economic Environmental
People and animals can die Businesses often have to Floodwater contaminated
shut down as premises are with sewage and rubbish can
inundated and power pollute rivers
supplies are affected
Floodwater is often Rescue work and repairs are River banks are eroded
contaminated with sewage, usually costly
which can lead to a lack of Insurance premiums go up
clean drinking water after floods
Contaminated water can also Unemployment levels often River sediment is deposited
put people at risk of diseases…read more

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Flood Management
Flood management strategies seek to reduce the effects of flooding on the human
The main strategies can be grouped as follows:
Structural methods
River basin management
Modifying the burden of loss
Bearing the cost of flood damage
The combination of methods used to combat the threat from flooding varies greatly from
country to country.
Developing countries may avoid expensive engineering solutions for economic reasons and
rely on bearing the loss when it occurs.…read more

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Hard Engineering Defences
Defence How it works Disadvantages
Dams Huge walls built across rivers Very expensive
A reservoir is built behind Land is flooded when
Flood water caught by dam reservoir is created
Prevents flooding downstream Affect wildlife
Water is released as steady flow Trap sediment
Cause floods if they burst
Flood walls Increase the height of the channel Restrict access to the
Stop water spilling onto the floodplain riverside
Levees Embankments built along rivers Quite expensive
The river can hold more water without…read more

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Soft Engineering Defences
Scheme How it works Disadvantages
Land use management Planning restrictions to Restricts development
prevent buildings or roads Problem if there's a shortage
being constructed on flood of housing
plains Can't be used in areas that
More water can infiltrate so are already urbanised
less surface runoff which
reduces discharge
Wetland and bank Wetlands store flood water Less land is available for
conservation and also slow it down farming
Reduces flooding
Gives natural protection
from flooding
Planting trees and shrubs
increase interception…read more

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Floodplain Zoning
Areas of a floodplain that are likely to be affected can be mapped as zones of relative risk.…read more


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