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

Find out more about human and physical causes of flooding.

Relief can increase flood risk because:

• Steep sided slopes mean that it is hard for infiltration to occur which leads to greater surface run-off
• Low lying flood plains are at risk of flooding because they do not have enough gradient to move the water on quick enough. This risk increases when the soils have a high clay content.
• Upland areas are more likely to experience rain due to relief rainfall. This increases the likelihood of high levels of precipitation and therefore surface run-off.

Find out more about human and physical causes of flooding.

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.

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

• Building new infrastructure e.g. roads and paths
• Building new houses
• Disappearing gardens

Find out more about human and physical causes of flooding.

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

Find out more about human and physical causes of flooding.