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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:…

Page 2

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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…

Page 3

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

Urbanisation Urban areas have large areas of
impermeable tarmac and concrete, so when
it rains surface runoff is very rapid

Gutters and drains quickly take runoff to

Both of these…

Page 4

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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,…

Page 5

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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…

Page 6

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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…

Page 7

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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…

Page 8

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

Zone A: Prohibitive Zones Areas nearer to the channel with a relatively high
risk of flooding
Essential waterfront developments may be permitted
but future development is unlikely to be allowed…


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