Fluvial Depositional Landforms | Types of Deltas

Environment

Fluvial Depositional Landforms are landforms created by the depositional activity of rivers.

Landforms and Cycle of Erosion

Fluvial landforms and Cycle of Erosion – Erosional Landforms [Previous Post: Fluvial Erosional Landforms – Drainage Patterns – River Valley] and Depositional Landforms [This Post].

  • Glacial landforms and Cycle of Erosion
  • Marine landforms and Cycle of Erosion
  • Arid landforms and Cycle of Erosion
  • Karst landforms and Cycle of Erosion

Fluvial Landforms and Cycle of Erosion

  • The landforms created as a result of degradational action (erosion) or aggradational work (deposition) of running water are called fluvial landforms.
  • The fluvial processes may be divided into three physical phases – erosion, transportation and deposition.

Fluvial Depositional Landforms

  • 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.
  • Various landforms resulting from fluvial deposition are as follows:

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.
Alluvial Fans-Cones fluvial
Alluvial Fans-Cones

Natural Levees

  • 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.

Natural Levees - flood barriers

Delta

  • 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 rejoin to form a network of channels.

A delta is formed by a combination of two processes:

  1. load-bearing capacity of a river is reduced as a result of the check to its speed as it enters a sea or lake, and
  2. clay particles carried in suspension in the river coagulate in the presence of salt water and are deposited.
  • The finest particles are carried farthest to accumulate as bottom-set beds.
  • Depending on the conditions under which they are formed, deltas can be of many types.

Delta -river mouth

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.

Arcuate or Fan-shaped delta - nile

Bird’s Foot Delta

  • This type of delta emerges when limestone sediment deposits do not allow downward seepage of water.
  • The distributaries seem to be flowing over projections of these deposits which appear as a bird’s foot.
  • The currents and tides are weak in such areas and the number of distributaries lesser as compared to an arcuate delta. Example: Mississippi river.

Bird’s Foot Delta mississippi

Estuaries

  • 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.

Estuaries-judson estuary

Cuspate Delta

  • This is a pointed delta formed generally along strong coasts and is subjected to strong wave action. There are very few or no distributaries in a cuspate delta.
  • Example: Tiber river on west coast of Italy.

Cuspate Delta

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