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In this lesson we are going to discuss the factors affecting river deposition and some of the features formed by river deposition

Answer Text:
Deposition
- Laying down of some of the load carried by the river when energy decreases.

Factors Influencing Deposition
a) Gradient
When gradient reduces the river’s speed decreases and hence its energy is reduced causing it to drop some of the heavy load.
b) Rivers Volume
When rivers volume decreases its energy also decreases causing it to deposit heaviest load then lighter ones.
c) Obstacles
Obstacles such as swamp vegetation and rock outcrop reduce the river’s speed and also trap some of the load thereby facilitating deposition.
d) River Bed Width and Depth
Where a rivers channel becomes wide and shallow there is less water per unit area and hence the river has lower capacity to transport so deposition of
excess load begins.

Resultant Features of River Deposition
a) Alluvial Fans and Bajadas
- Fan shaped deposits of alluvium.


Formation
- The river flowing through a narrow channel enters a plain from a higher ground and suddenly spreads out.
- There is a sudden loss of velocity causing the river to scatter alluvium all around to form an alluvial fan.
- Alluvial fans merge to form a continuous feature called bajada or piedmont fan.

b) Meanders and Oxbow Lakes
Meanders are loop-like bends in a rivers course.
Oxbow lake is a horse shoe shaped section of a former river.
Formation

- In mature stage river flows sluggishly due to reduced gradient.
- It meets an obstacle and flows around it.
- Erosion is greater on the outer bank and deposition on the inner bank causing the river to form loop like bends.

- Erosion continues on the outer bank (bluff) narrowing the land between the two outer banks forming a pronounced
meander e.g. on rivers Yala, Nzoia and Tana.

- During the floods when the river has more energy it cuts across the narrow land.
- The former bends are cut off by deposition to form an oxbow lake e.g. Kanyaboli on R.Yala and Shakababo on R.Tana.

Flood Plains

- Wide gently sloping plain of alluvium on the floor of a river valley.
Formation
- A river meanders.
- There is erosion on outer bank and deposition on the inner bank.
- The process continues and layers of alluvium deposited on inner bank join to form a plain e.g. Nzoia and Yala flood
plains.