Case study of flood risk management

• What happened to prevent future flooding?

  The environmental agency invested £10 million into several flood defences, such as:

  • Widening and deepening the river channel (capacity)
  • Removing low bridges and replacing them with wider bridges - water could flow freely underneath the bridge and the bridge wouldn't act like a dam due to debris build up
  • Raising the car park and using a permeable surface (height)
  • Tree management - dead trees were removed to prevent them being swept away, causing bridge dams. Land owners were encouraged to maintain vegetation and plant new trees.

  
• Location

  The town of Boscastle is located in South East England, on the North coast of Cornwall on the Bristol Channel. The town is 43 miles north west of Plymouth and 230 miles east of London, slightly south east.
• What happened?

  On the 16th August 2004, a devastating flood swept through Boscastle, a small village on the north Cornwall coast, with two billion litres of water rushing down the valley, causing the river to overflow.
• Social issues

  The rebuilding projects and construction of flood defences took several years which meant the lives of local people were disrupted for sometime. The risk of flooding has been reduced making Boscastle safer. The defences would not protect against a flood the same size as the one in 2004. The new bridge is not popular with local people as it is out of character compared to the rest of the building.
• Economic issues

  The risk of flooding has been reduced. Therefore, there is less risk of damage to property and businesses. The flood-defence scheme cost over £4 million. However, the scheme could have been significantly better, though some options were too expensive.
• Environmental

  Biodiversity has improved as have the river habitats. Vegetation in the area is now managed.
• Human Causes of the flood

  • Many tourists were in Boscastle during the day, as it was the middle of the summer holidays. This meant that a higher than normal number of people needed to be evacuated.
  • Many trees had been cut down for farming. This limited interception and water went straight into the river channel.
  • Increase in buildings meant that there were more impermeable surfaces which directed water back to the river faster.
  • A few old arch bridges got blocked up with the flood debris. The bridge acted like a dam and eventually smashed through causing a surge of water up to 5m high.
• Physical causes of the flood

  • Rain for 12 out of 14 days in August.
  • Steep valley sides - water flowed into the river channel very quickly
  • The rock in the local area is slate which does not allow perculation.
  • The soils were quite thin and made up of impermeable peat soils. These became saturated so water became surface run-off very quickly.
  • A depression brought a thunderstorm on 16 August with over 200mm (1 months worth) of rain in 24 hours.
  • There were very few trees to absorb water and slow the amount of water going into the river.
• Effects of the flood

  • Homes, businesses and cars were swept away, affecting more than 1,000 people. Income from tourism was lost. This had an impact on livelihoods and the local economy.
  • There were vast numbers of subsequent insurance claims.
  • No lives were lost, partly due to the rapid response of the emergency services.
  • More than 70 vehicles were washed downstream by the flash-flood in Boscastle.