Meander Formation
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Meander Formation

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This powerpoint looks at the formation of meanders. It leads students through their formation and then ends with an exam question.

This powerpoint looks at the formation of meanders. It leads students through their formation and then ends with an exam question.

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Meander Formation Presentation Transcript

  • 1. Meander Formation
  • 2.  
  • 3.  
  • 4. Learning Outcomes
    • You will be able to explain the sequence involved in the formation of a meander.
    • You will be able to explain the sequence using the key terminology.
    • KEY WORDS – helicoidal flow
    • sinousity
    • thalweg
    • centripetal force
  • 5.  
  • 6. Meander Formation
    • Riffles and Pools
    • Riffle – a shallow part of the channel
    • Pool – a deep part of the channel
    • On average pools occur 5-6 times the width of the river bed
  • 7. Meander Formation
    • The riffle reduces the hydraulic radius of that section of the channel as the water flows inefficiently over it.
  • 8.  
  • 9. Asymettrical shape
  • 10. The meandering Thalweg
    • Thalweg – the line of fastest flow in a river
  • 11. Centripetal Force
    • At times of high flow the water is thrown around the riffles and is thrown to the edge by centripetal force eroding and undercutting it. (MAINLY ABRASION AND HYDRAULIC ACTION)
  • 12. Deposition
    • Slower flow on the inside of the bend leads to depostion there.
    • It is slower because the reduction in the rivers efficiency being reduced due to the frictional contact with the river bed.
  • 13. Helicoidal Flow
    • The movement of water in a meander has been found to move from the outside to the inside.
    • This helicoidal flow allows material eroded from the outer bank to be moved to the point bar on the inside of the next meander downstream.
  • 14. Helicoidal Flow
    • Corkscrew motion
    • In bends, water forced to outside of bend hits bank with force
    • Water piles-up on outside of bend
    • Forced downward along river cliff, back towards point bar
    • Transfers and reverses motion around next alternating bend
  • 15.  
  • 16. Exiting the meander
    • As the water exits the meander the channel becomes shallower. This reduces the hydraulic radius thus increasing deposition.
    • As such new riffles are created.
  • 17.  
  • 18. Sinuosity
    • Actual channel length
    • Straight Line Distance
    • A sinuosity of 1.5 is the dividing line between a straight and meandering channel.
    = sinousity
  • 19. Point Bar River Cliff Thalweg
  • 20. Thalweg Deposition Point Bar Helicoidal Flow River Cliff Abrasion Hydraulic Action Riffle Pool Sinuosity Meander Centripetal Force
  • 21.
    • Explain the formation of a meander
    • (8 marks)
  • 22.  
  • 23.  
  • 24. Meander Formation
    • Explain the formation of a meander using
    • helicoidal flow
    • sinousity
    • thalweg
    • centripetal force