Transportation
Rivers will pick up and move rocks, silt and other material as they move downstream. There are four main ways in which this is done:
Solution: Minerals that are dissolved into the river are carried along.
Suspension: Fine material is swept along in the water.
Saltation: Small pebbles and stones are bounced along the riverbed.
Traction: Larger stones are rolled along the river bed.
Rivers use energy to move material, and a rivers energy level changes between source and mouth.
When energy levels are very high, large rocks and boulders can be transported. Energy levels are usually higher near a river's source, where it's course is steep and valley narrow. Energy levels also rise in times of flood.
When energy levels are low, only small particles can be transported. Energy levels are lowest when velocity drops as a river enters a lake or the sea.
Deposition
When a river loses energy, it will drop, or deposit the material that it is carrying.
Deposition can occur when a river enters an area of shallow water or when the volume of water decreases, for example, after a flood or during a drought.
Deposition commonly occurs at the end of a river's journey, when it enters a lake or the ocean.
Deposition at the end of a river can form river deltas.
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