River transportation processes. Image credit BBC.

River transportation processes. Image credit BBC.

ZIMSEC O Level Geography Notes: River Transportation Processes.

  • Any energy left after a river has overcome friction is used to transport sediment.
  • This energy varies directly with a river’s discharge, velocity and turbulence
  • That is if they increase the amount of a river’s energy to erode and transport also increases until a river reaches flooding level when deposition is likely to occur due to an increase in the wetted perimeter and thus friction.
  • There are three main processes by which a river’s load is transported:
  • suspension, solution and bedload (sometimes divided into saltation and traction making them four methods instead of three in this case).

Suspension

  • This is when light silt and mud floats along with the water.
  • Very fine particles of silt and clay are dislodged and carried away in the turbulence of the flowing water.
  • The greater the turbulence the greater larger the quantity and size of particles picked up by and carried away by the river.
  • This partly explains why flooded river often have mud coloured water, it is due to the heavy amounts of suspended material with the water.
  • The suspended material usually forms the largest part of a river’s total load.
  • It increases in amount towards a river’s mouth also giving the black/brownish colour to the water that is similar to that of most rivers after a storm.

Solution/Dissolved Load

  • Is when material dissolves in the water and is carried away  in solution form for example rock salt.
  • Flowing water within river channels almost always contain acids in the form carbonic and nitrous acids especially after a storm or due to pollution.
  • This dissolves the bedrock especially if it is soluble for example limestone.
  • It dissolves in water and is carried away in solution form.
  • This is a very active form of transportation in limestone regions and in other regions it forms a comparatively small part of the load.

Bedload

  • Is divided into two processes traction and saltation.
  • Saltation is when smaller particles bounce along the bed of the river.
  • Traction is when larger boulders and pebbles roll and are dragged along the river’s bed.
  • Since larger particles cannot be picked up by the current they are moved along the bed of the river in these two ways.
  • Saltation happens when pebbles,sand and gravel are temporarily lifted up by the river’s current and bounced along the bed of the river in a hopping motion.
  • Traction occurs when the largest cobbles and boulders roll or slide along the bed of the river.
  • The largest loads can only be moved in this way during flood periods for example after a storm.

To access more topics go to the Geography Notes page.

 

 

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