Heavier rainfall plus sea level rise – which make storm surges bigger and more likely to breach coastal defences
The flooding across England in summer 2007 and in Cumbria and Aberdeenshire during November 2009 highlighted the various forms of flooding that the UK faces. It also highlighted the significant and widespread impact on people, businesses, infrastructure and essential services that flooding can cause. The rising temperatures and sea levels associated with climate change are likely to increase the frequency and severity of extreme weather events, and hence the flood risks across the UK.
The three main types (or sources) of flooding are from the sea (coastal or tidal), from rivers and streams, and from surface water (caused by excess rainfall before it enters the drainage system). All three forms of flooding could occur during a single storm. A further scenario, such as a major reservoir dam collapse or failure, could bring about rapid flooding and is included in the major industrial accidents section. The term ‘inland flooding’ is used to describe all forms of flooding other than coastal.
Coastal flooding has the potential to have the most widespread impact in a single event.
The last significant event of this type to affect the UK was in January 1953 when the east coast of England suffered one of the biggest environmental disasters ever to have occurred in this country. Flood defences were breached by a combination of high tides, storm surge and large waves. Coastal towns in Lincolnshire, Norfolk, Suffolk, Essex and Kent were devastated as sea water rushed into the streets. Over 600km2 of land were flooded, 307 people killed and 200 industrial facilities were damaged by floodwater. Over 32,000 people were safely evacuated. A month after the flooding, the estimated cost was £40 –50 million, the equivalent of around £1 billion today, not including the cost of relocation and interruption of business activity.
Since 1953, much work has been done to improve flood defences. Consequently, the likelihood of defences failing or being overtopped by sea tides is now substantially lower. In particular, the construction of the Thames Barrier in London and associated flood defence systems along the east coast of England now means that there is a good level of protection against sea and tidal surges. In Wales, large-scale coastal defence schemes are being processed at a number of locations including Borth in Ceredigion, Colwyn Bay in Conwy, West Rhyl and Denbigh in Denbighshire and Riverside in Newport. These schemes are being taken forward with the support of the European Regional Development Fund and are part of a programme aiming to reduce risk for over 3,000 properties across Wales. However, the improvements in flood defences have led to significant development of homes, businesses and infrastructure behind them. The consequences of any breach or overtopping of flood defences will now be much greater than previously experienced.
The frequency of inland flooding is increasing; this is evidenced by several examples of river and surface water floods over the last few years. Of these, the events of summer 2007 were the most widespread. In June–July 2007, severe rainfall during an extremely wet summer led to the flooding of 48,000 households and 7,300 businesses across England. Other effects of recent flooding have included the closure of primary transport routes, the loss of some critical services such as electricity, telecommunications and water supplies, and large numbers of people requiring evacuation and alternative accommodation. Businesses as well as homes have been made inaccessible for many months while buildings dry out and damage is repaired. The flooding in Cumbria in November 2009 caused six bridges to collapse, severing the road network and cutting off communities.