Fluvial deposition

Alluvium is soil or sediments deposited by a river or other running water. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. It can be found in great thicknesses on the flood plain, especially where levees are formed.

Fluvial deposition is encouraged by several factors:

• A river carrying a large load will deposit more than a river carrying a small load as the amount of load provides the material for deposition. The geology of the area through which the river is flowing we impact upon the amount of load.
• A reduction in river velocity such as on the inside of a meander will cause a increase in deposition as velocity and therefore energy is needed for a river to carry it's load.
• A sudden change in the fluvial dynamics, for example when a river enters a lake or a river flows into the parapets of a bridge will interrupt flow, effect the amount of energy the river has and therefore it's ability to carry sediment.
• A fall in the volume of the water, for example periods of low flow (during droughts) will affect the rivers efficiently and therefore the amount of energy available to carry sediments.

Questions

1. What is alluvium?
2. Describe four factors that encourage fluvial deposition.

3. What is meant by the term sediment? [1 mark]
4. What is meant by the term deposition? [1 mark]
5. What natural feature (landform) is shown at Y? [1 mark]
6. Describe and suggest reasons for the likely differences in the amount of deposition accruing at points X, Y and W. [6 marks]
7. What natural feature is shown at W? [1 mark]