Building a new housing estate on the floodplain increases the risk of flooding because the surface becomes impermeable due to the construction of houses, tarmac roads and concrete pavements. Surface run-off increases leading to a rapid increase in a river’s discharge.

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Geology can increase the risk of flooding when:

• The upland bedrock is impermeable, such as slate, which means there is more surface run-off
• Soil in low lying areas is made up of clay. Because it is so compact it is difficult for infiltration to occur.
• Areas of permeable rock, such as limestone, become inundated with water leading to increased surface run-off

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Three ways humans can increase the risk of flooding in rural areas are:

• Deforestation
• Intensive farming, leaving fields bare in the winter
• Overgrazing
• Increased use of polytunnels

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Natural ways flood risk can be increased include:

• heavy rainfall caused by depressions causing heavy, continuous rain which saturates the soil. The land can no longer absorb water as it is saturated increasing surface run-off, higher river discharge and flooding.
• sudden downpours occurring following a very dry period can lead to flooding because the surface is baked hard. Surface run-off occurs as water cannot infiltrate leading to higher river discharge and flooding.
• sudden snowmelt releases stored water that flows over the land as surface run-off
• the loss of vegetation cover through drought or disease can lead to flooding as less interception occurs so more precipitation reaches the surface leading to increased surface run-off.

Find out more about human and physical causes of flooding.

A change from pastoral to arable farming increases the risk of flooding because once crops have been harvested the soil is sometimes left bare in the winter. This reduces interception because there is no vegetation.

Find out more about human and physical causes of flooding.