Flooding
Overview
Everyone should be aware of the dangers of flooding. It can endanger lives and property.
Who is at risk from flooding? » River flooding » Sewerage flooding » Flooding on coasts and in estuaries » How do we manage the risk from flooding?
Who is at risk from flooding?
Flooding happens naturally and can’t be completely avoided. River flood plains and low-lying coastal areas are at higher risk than other areas. Around five million people, in two million properties, live in flood risk areas in England and Wales. Changes in climate, such as more severe storms and wetter winters, will increase that risk.
Roads, railways, housing and commercial developments are often built in floodplains because it is relatively easy and cheap to build there. Some 11 per cent of new homes are built in flood risk areas in England.
Development on a flood plain reduces the space available to floodwaters. The speed and height of the flood increases as it moves down stream.
In some cases development in the flood plain acts like a dam, increasing flooding upstream. Drainage systems and hard surfaces, such as roads and car parks, can also increase flooding by quickly transferring rainwater into rivers.
Any new developments on floodplains increase flood risk. We advise local authorities on flood risk when they are considering planning issues. We also encourage using sustainable drainage systems in new developments to limit the chance of flooding.
Anyone who has experienced flooding will confirm the stress, disruption and grief that can be caused as well as the physical danger. To find out more follow the 'Am I at risk of flooding?' link below.
River flooding
River channels can only carry a limited amount of water. Heavy rain or sudden snowmelt can cause rivers to rise to the point where they overtop their banks. During a flood, the excess water flows onto the low-lying areas on either side of a river – the flood plains. Periodic flooding of low-lying areas nourishes the soil. Flooding has benefited farmers in this way for centuries.
A devastating river flood hit the village of Boscastle in Cornwall on August 16 after 200 millimetres (8 inches) of rain fell in 24 hours. Floodwater rampaged through the village taking cars, trees and other debris with it. Around 2 million tonnes (440 million gallons) of water flowed through Boscastle that day.
There is some evidence that the frequency of peak river levels is increasing (Indicator: Flood Levels - click to enlarge). There is evidence that flooding comes in cycles and the rivers with a long data record will give a more reliable assessment of trends. The two rivers with the longest records are the Severn and the Wye. The Severn shows a constant trend, but the Wye has an increase in frequency of peak river levels.
Sewerage flooding
Very heavy rain can result in severe, but localised flooding. Some sewerage systems, for example London’s Victorian system, can be easily overloaded in heavy rain. Properties can be flooded and large amounts of raw sewage released into water bodies. The ecological consequences can be severe. In August 2004 heavy rainfall in London lead to appalling pollution events that killed thousands of fish, left sewage debris and a foul smell along the foreshore of the tidal Thames, and significantly increased E. coli levels in the river. The Thames Tideway Strategic Partnership are developing a solution to London's problem. It will need substantial investment.
Flooding on coasts and in estuaries
Low-lying, open coastal areas are at risk of being flooded (Figure 1 - click to enlarge). In estuaries, flooding can occur as a result of ‘surges', caused by the combined effects of atmospheric pressure, high tides and high winds. In addition, sea levels around the UK are about 10cm higher than they were in 1900.
We can control the frequency, extent and size of flooding to some degree. We own and operate several tidal barrages, including the Thames Barrier, which protects 150km² of London that lies below the high tide level.
The Barrier was closed 72 times to protect London from tidal flooding between 1983 and 2007(Indicator: Thames Barrier closures - click to enlarge).
The Barrier can also be used to reduce flood risk from high rainfall upstream. In these cases the Barrier closes against the tide to keep water levels low in the down stream portion of the Thames so that increased water volume from upstream has somewhere to go. For example, between New Years’ Day and 8 January 2003 high rainfall upstream and high spring tides increased London’s flood risk. During this period we closed the barrier a record 14 times. This is double the previous record of seven consecutive closures during the floods of October 2000.
How do we manage the risk from flooding?
We use regulation, land use planning, flood and coastal defences, flood warning systems and emergency response procedures to limit the impact that floods can have on people living in an 'at risk' area.
However, flooding is a natural hazard and we must accept that we cannot eliminate flood risk entirely, only reduce it.
This work is worth doing. Flood damage already costs about £1billion a year and our flood risk management prevents further yearly damages of £3.4 billion. But we can’t defend everywhere.
Damage costs from flooding are predicted to be as much as £25 billion under a worst case climate change scenarios in the 2080s.
Since 1988 the cost of repairing the damage from extreme weather events and floods has increased by 60%. Climate change in the UK could bring more extreme weather conditions, including more frequent floods and storms.
We estimate that over the next 80 years we will need to spend £22 to £75 billion on flood defences in England and Wales to combat the effects of climate change.
- Current Flood Warnings in Force
Allows you to view flood warnings in place and flood warnings issued. Updated every 15 minutes. - Flood
Around 5 million people live in flood risk areas in England and Wales. We warn people about flooding and build flood defences. - Am I at risk of Flooding?
Use our Flood Map to find the likelihood of flooding in your area. You can also check current flood warnings in force from here and find more details on how flooding could affect your home insurance.
- Met Office
Click here to get more information from the Met Office website.
Environmental indicators:
