Rivers

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  • Created by: katie
  • Created on: 04-04-13 14:48

Hydraulic Action

  • The force of the water on the bed and banks of the river.
  • It is particularly powerful when the river is in flood.
  • The force of the water wears material away from the bed and banks of the river. 
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Abrasion

  • The river carries particles of sand and silt.
  • It moves pebbles and boulders at times of high flow.
  • The material rubs against the bed and banks of the river and wears them away.
  • Also called corrasion.
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Solution

  • Some rock minerals, such as calcium carbonate (in limestone and chalk) slowly dissolve in river water, which is sometimes slightly acidic. 
  • Also called corrosion
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Attrition

  • The load being carried by the river collides and rubs against itself, breaking up into smaller pieces. 
  • The rough edges become smooth, forming smaller, more rounded material. 
  • Eventually the particles are reduced to sand and silt sized particles
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Traction

  • Boulders and pebbles are rolled along the river bed at times of high discharge
  • This requires the most energy because the boulders are heavy so a lot of energy is needed to push them along the river bed. 
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Saltation

  • Sand sized particles are bounced along the river bed by the flow of water
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Solution

  • Some minerals, such as calcium carbonate, dissolve in water
  • This requires very little energy
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Suspension

  • Fine clay and sand particles are carried along within the water, even at times of low discharge
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Deposition

  • This is when a river drops its load. It could be because:
    • There is a smaller volume of water - not enough energy to carry the load
  • The river is shallower
    • There is more friction so the river slows down and less energy
  • There is a bend/meander in the river
    • It slows down on the inside bend and it is shallower
  • There is human activity, e.g. a dam
    • There is a lot of depostition behind the dam
  • Input of sediment
    • There is too much sediment so it is too heavy to carry, e.g. a landslide
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