Case Study - Rivers MEDC - Lynmouth

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Causes of the Lynmouth Flood

  • The small but steep sided drainage basin in which Lynmouth was situated increased the risk of flooding in the area. The steep sides encouraged greater surface runoff and combined with the small drainage basin size meant any water could reach the river fairly quickly
  • This was made worse by the high drainage density of the area due to the impermeable rocks of the area around Exmoor which formed the source of the river; again increasing the amount of surface runoff following rainfall
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Causes of the Lynmouth Flood cont.

  • Prior to August 15th 1952 Lynmouth had received above average rainfall for 12 out of the first 14 days of the month meaning the soils were already saturated and the river levels high.
  • On August 15th a heavy thunderstorm resulted in 200mm falling in 14 hours, one of the three heaviest rainfalls recorded in the UK. This heavy rain combined with the saturated ground and rapid surface runoff resulted in a huge volume of water flowing down the river.
    • As Lynmouth is situated at the confluence of the East and West Lyn rivers the volume of water was increased further at this point and the was far beyond the capacity of the river channel causing the river to burst its banks.
      • This resulted in devastating floods as the West Lyn which had been diverted during the construction of parts of Lynmouth retook its natural course, flowing straight through the village.
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  • Debris built up behind bridges resulting in the build up of a flow of water which eventually burst resulting in torrents of water flowing through Lynmouth with 34 people being killed in the disaster
  • The West Lyn river took its original course flowing straight through Lynmouth destroying 90 houses and hotels
  • 130 cars and 19 boats were also lost, swept into the river or out to sea as the force of water was able to transport large amounts of debris (including gigantic boulders)
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Flood Management

  • The mouth of the East Lyn was widened to increase capacity and allow water to quickly pass into the Bristol Channel
  • The West Lyn was straightened to increase channel efficiency - straightening the channel reduces friction and increases velocity, enabling water to travel through the channel as quickly as possible making it more efficient in coping with flood waters
  • The West Lyn was not rediverted, instead being allowed to follow its natural course
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Flood Management cont.

  • Floodplain zoning was used to identify areas around the river most at risk from flooding. Building restrictions were then put in place with areas close to the river which are most prone to flooding being left as open spaces such as car parks.
  • Bridges were made wider and taller to allow flood water to tr avel quickly beneath them and to reduce the likelihood of debris becoming trapped and acting like a dam as had happened in 1952
  • Embankments were built by the river to increase channel capacity and reduce the likelihood of flooding
  • More trees were planted upstream in the source area to try and reduce initial surface runoff through interception and the soaking up of water. Tree roots also help to improve infiltration by opening up the soil and slowing down the rate at which water reaches the ground
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