Flood risk

Flooding is a natural event. It occurs when there is heavy rainfall that fills rivers and streams above their normal capacity, or if there are very high river or coastal tides that cause levels to rise or surge.

The excess water that gathers cannot be restrained by normal boundaries (such as a river embankment) and follows the path of least resistance.  This means areas that are low lying and close to the source of a flood will be the most vulnerable.

Floods can also occur when rainwater collects on the ground and cannot find a source to drain into. A typical example is surface water run-off (for example, if you are located at the bottom of a hill or slope of ground).

Localised flooding mainly happens when the ground cannot absorb any more water in a particular area, or if sewers and underground drains become blocked or cannot cope with the excess water trying to drain into them.

When we talk about flood risk we mean two things:

  • The likelihood of a particular flood happening, best expressed as a chance or probability over a period of one year. For example, 'There is a 1 in 100 change of flooding in any given year in this location'
  • The impact or consequences that will result if the flood occurs

It is important to know both how high the probability is of flood occurring and the severity of any impact (which may change depending on how extreme the flood is).

Only by determining both for a range of flood events of different sizes can the risk to a particular area be assessed. 

When submitting an application for planning permission you might need to provide a Flood Risk Assessment.  Find out more about applying for planning permission.