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.

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