Case study: Boscastle Flood
Case study on the Boscastle flood
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?- Created by: Gabzay
- Created on: 24-04-13 12:41
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- Boscastle Flood
- Precautions put in place
- Improve culvert to carry more excess water away after heavy rain
- Widen and lower River Valency so it has more capacity to carry water
- Braided river channel to slow the flow of water
- Allows river to deposit large sediment before it reaches the village
- Raise the height of the car park and add barriers to prevent cars from washing away
- Build houses on raised platforms
- Replace low bridge (which acted like a dam) with a high bridge
- Debris grills placed at entrances of culverts and along edge of forests facing onto the river
- Flood warning box which sends information to the Environment Agency
- Impacts
- 116 cars swept away - 32 never seen again
- 58 properties flooded - 4 swept away
- 4 foot bridges swept away
- Sewage system overwhelmed by volumes of water
- Emergency services were overwhelmed
- 23,000 properties lost power
- 300 metres worth of sewer pipes were blocked or washed away
- Key Players
- Environment Agency
- Issues flood warnings, forecasts and implements major incident plans
- Monitors water levels and flows
- Local authorities
- Issues flood warnings, forecasts and implements major incident plans
- Local authorities
- Has a supervisory role over all flood defenses
- Local authorities
- Local authorities
- Police
- Co-ordinate emergency response in major floods
- Helps save lives and property
- Fire services
- Rescues people trapped by flood water
- Can pump water out of buildings
- Volunteer-run weather station
- Environment Agency
- What happened?
- Most widespread and long lasting flood (172 days of rain)
- Embankments along river sides failed to protect from flooding
- England's wettest year since records began in 1910
- 200mm of rain in 24 hours - mostly over a 5 hour period
- Peak intensity of rainfall was 300mm per hour
- Very localised storm
- Tarmacked (e.g. Old Road) / parking areas acted as false river beds creating flash floods
- 16th August 2004
- Causes
- Convergence of River Jordan and River Valencey is in centre of Boscastle
- Trough (localised rain and thunderstorms) hung over Bostcastle
- Geology - underlying rock is granite which is impermeable leading to high levels of run-off
- Many micro-climates because it is a hilly area
- The shorter the lag time, the more likely the flood
- Farming
- Ploughing up and down hills rather than across
- Creates channels which increase the speed rainwater reaches rivers
- Ploughing up and down hills rather than across
- Urbanisation
- Particularly on flood plains
- Impermeable surfaces reduce infiltration and increase run-off into drains and rivers
- Destruction of natural environments
- Increases run-off
- E.g. destruction of wetlands and grasslands, deforestation
- Precautions put in place
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