Rivers deposit sediments in different parts of their courses and thus form three major types of landforms which are called Fluvial Depositional Landforms such as alluvial fans cones, natural levees and deltas.
- The depositional action of a stream is influenced by stream velocity and the volume of river load.
- The decrease in stream velocity reduces the transporting power of the streams which are forced to leave some load to settle down.
- Increase in river load is effected through accelerated rate of erosion in the source catchment areas consequent upon deforestation.
Alluvial Fans and Cones
- When a stream leaves the mountains and comes down to the plains, its velocity decreases due to a lower gradient.
- As a result, it sheds a lot of material, which it had been carrying from the mountains, at the foothills.
- This deposited material acquires a conical shape and appears as a series of continuous fans. These are called alluvial fans.
- Such fans appear throughout the Himalayan foothills in the north Indian plains.
- These are narrow ridges of low height on both sides of a river, formed due to deposition action of the stream, appearing as natural embankments.
- These act as a natural protection against floods but a breach in a levee causes sudden floods in adjoining areas, as it happens in the case of the Hwang Ho river of China.
- A delta is a tract of alluvium at the mouth of a river where it deposits more material than can be carried away.
- The river gets divided into distributaries which may further divide and re- join to form a network of channels.
- Arcuate or Fan-shaped
- This type of delta results when light depositions give rise to shallow, shifting distributaries and a general fan-shaped profile.
- Examples: Nile, Ganga, Indus.
- Sometimes the mouth of the river appears to be submerged.
- This may be due to a drowned valley because of a rise in sea level.
- Here fresh water and the saline water get mixed.
- When the river starts ‘filling its mouth’ with sediments, mud bars, marshes and plains seem to be developing in it.
- These are ideal sites for fisheries, ports and industries because estuaries provide access to deep water, especially if protected from currents and tides.
- Example: Hudson estuary.
Fluvial Depositional Landforms,Fluvial Depositional Landforms
Read more : Erosional Landforms