the lynmouth flood 1952

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The Lynmouth Flood 1952. Lynmouth Floods 1952. A flash flood! Was this natural disaster made worse by human activity? What lessons can be learned from the disaster?. Where is Lynmouth?. Location: Country: United Kingdom Region: South West England County: Devon - PowerPoint PPT Presentation

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Lynmouth Floods 1952

The Lynmouth Flood 19521Lynmouth Floods 1952A flash flood!Was this natural disaster made worse by human activity?What lessons can be learned from the disaster?

2Where is Lynmouth?

Location:Country: United KingdomRegion: South West EnglandCounty: Devon

A small coastal town , Lynmouth is located in steep-side narrow valley at the confluence of two rivers the East Lyn and the West Lyn.

3What caused the flood?4Flash Floods

5What caused the flood?Meteorology -The WeatherCombination of factors:Dry summer up to early AugustPeriod of heavy rain leading up to Aug 15thExtreme rainfall event on August 15th weather on line

Image from BBC Devon6The Weather

Low pressure system centred over the South Devon/Dorset coastA zone of warm damp air produced heavy thunderstorms during afternoon of Aug 15thLate evening the Low moved east & caused a rapid movement of cold air to force its way up the northern slope of Exmoor.This cold air shunted the already unstable air upwards, accelerating uplift -chilling of damp air and produced violent downpour!

7What happens in a Low Pressure System?

8Early AfternoonThunderstorms unstable warm air risingExmoor warm ground9August 15th 1952 Late AfternoonWedge of Cold Air forces warm air upwardsRapid ChillingRapid CondensationMassive downpour Saturated groundRUN-OFF10Rainfall in August 1952

Graph shows rainfall in the 2 days leading up to the disaster.Peaks at 5pm on the 15th and 9pm on the 16th August230mms of rain in 14 hrs!11Rainfall on 15 August 1952

The map opposite shows the area of maximum rainfall

Notice:Over 204mm on Longstone Barrow & The Chains area of moorland we visitedNumerous tributaries feed East and West Lyn RiversRivers meet (confluence) at Lynmouth

Figure from Lyn in Flood, Keene & Elsom, Oxford Brookes Univ.199012What caused the flood?Relief /Topography the shape of the landThe Lyn Valleys are both narrow and steep sidedThe rivers drop steeply from the moors of ExmoorBoth rivers meet at the end of the drop at Lynmouth

Image from Google Earth13What caused the flood?Relief /SoilsThe black, peaty, soils on Exmoor are very thin.The heavy rain in August meant that they became saturated.The rain falling on Aug 15th could not be absorbed by the soil and simply ran off, carrying the soil with it.

The Moors (taken 4 Sept 2009) 14The East Lyn Valley our walk!

Extract from Lynton Lynmouth Walking Map. www.croydecycle.co.ukDrop off pointWatersmeetTechnocentric bridgeEcocentric bridgeNotice the tight contours in the valley evidence of steep slopes!15The East Lyn Valley Narrow and Steep

16A Raging Flood in two confined valleys!13.6 million cubic meters of water fell on the drainage basin of the East and West Lyn Rivers.The water surged down the valleys picking up boulders weighing 50 tonnes.Rivers carried huge volume of soil from moorsTrees swept into riversBridges formed natural dams when they gave way a 12 meter high wall of water thundered through the town of Lynmouth.

BBC reportPathe Newsreel17How did Lynmouth Change?

Look the this map of Lynmouth as it was before the flood.

18This is Lynmouth today

Changes made to the town.

Both river beds widened and deepened.Soak-away areas built into river channelBanks strengthened and reinforcedBridges designed to allow flow of much larger volumes of water.Buildings in high risk areas not replaced or demolished

19Bridges Ecocentric or Technocentric?

Which bridge is designed to easily wash away and which is designed to resist a flood?20A very similar event!Boscastle Flood 2004Video News Report

http://www.youtube.com/watch?v=AszCGAETLt4&feature=player_embedde d21Beware the unexpected!

What do Lynmouth & Boscastle have in common?

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