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
        • Has a supervisory role over all flood defenses
          • 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
      • 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
        • 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

    Comments

    Abraham Somers

    It's good.

    Mr A Gibson

    A decent factual case study. Effectively categorized into "Cause", "Effect" etc. Add to your Rivers, Floods and Management revision materials.

    Gabzay

    Thanks! :)

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