Environmental Chemistry

River Deltas – Introduction, Formation, Types

The submission of sediments by a river near its mouth point before it drains into a body of water leads to the formation of river deltas. A river delta forms at the mouth of a river where the river deposits the sediment load which it carries. Moreover, it drains it into a slower-moving or static body of water.

River Deltas

Introduction to River Deltas

Formation of a River Delta usually occurs when the river joins a sea, estuary, ocean, lake, reservoir or in rare cases a slower moving river. The deltas of rivers are usually highly fertile areas and thus some of the most densely populated settlements of humans are based on such deltas. Major examples of major deltas of the world are the Nile River delta and the Ganges River delta.

Formation of River Deltas

There are various criterions which constitute the formation of a river delta. Under this segment of the article, we will discuss some of those points:

  1. The river needs to carry sufficient sediment to deposit at its mouth to form the delta.
  2. The tidal currents or waves of the river need to be weak. It is because the river is unable to carry the sediments into the body of water which it joins.
  3. The river must drain into a body of water that is either static or has a slow flow rate to prevent the fast removal of sediments carried by the river at its mouth.

When a river enters its last phase before it drains into another body of water, it is usually no longer confined to the channel in which it flows but its waters spread out as it enters another body of water. The spreading out of the river decreases its velocity and this, in turn, reduces its capacity to carry the great load of sediments with it. Hence, the sediments get deposited on the river bed and river banks. As the sediments build up over time, the river no longer flows through a single channel since the heavy deposits of sediments impede the flow of water.

Download River Deltas Cheat Sheet PDF

Types of River Deltas

1. Wave-dominated deltas

In wave-dominated deltas, wave-driven sediment controls the shape of the delta. Waves also cause deltas to retract and reflect by eradicating sediments from the river’s mouth.

2. Tide dominated deltas

A tide controls the shape of the delta in the case of tide-dominated deltas. Erosion plays a significant role in shaping such deltas. Distributaries are formed in such deltas when there is sufficient water in the region like during storm surges and floods. These distributaries gradually silt up and finally become non-existent. The Ganges river delta is a great and famous example of the tide-dominated delta.

Solved Question For River Deltas

Question: Write a short note on Gilbert Deltas

Answer: A Gilbert delta is formed when the sediments deposited to form the delta are coarse in nature. While some suggest that Gilbert deltas are formed at both marine and lacustrine locations, others suggest that they are formed when the river waters blend more easily with the waters of a freshwater lake. Moreover, usually in cases of rivers entering the sea or a salt lake, the waters of the river float.

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