- 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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- 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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- 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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- 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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- 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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- Sand sized particles are bounced along the river bed by the flow of water.
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- Some minerals, such as calcium carbonate, dissolve in water.
- This requires very little energy.
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- Fine clay and sand particles are carried along within the water, even at times of low discharge.
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- 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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