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).
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.
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.
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.