All questions of Landforms made by running water for UPSC CSE Exam

Neither of the statements is correct.

1. The first statement is incorrect. During annual or sporadic floods, it is not the hard materials that are spread over the low-lying adjacent areas, but rather a mixture of sediment, silt, and other organic material carried by the floodwaters. These materials are usually fine-grained and easily transported by the flow of water. As the floodwaters recede, they deposit this sediment, gradually building up layers of sediment over time. Levees, on the other hand, are natural or man-made embankments that are formed along the sides of a river to prevent flooding. They are not formed by the deposition of hard materials during floods.

2. The second statement is also incorrect. A floodplain is a flat or gently sloping area adjacent to a river that is periodically flooded. It is not formed by the accumulation of deposits in the riverbed or the dropping of material on the sides. Instead, a floodplain is formed over a long period of time as the river naturally meanders and changes its course. As the river meanders, it erodes its banks and deposits sediment on the floodplain, creating a flat and fertile area. The accumulation of sediment in the riverbed does not result in the formation of a floodplain.

To summarize, neither statement is correct. Floodplains are formed by the natural meandering of rivers and the deposition of sediment over time, not by the accumulation of deposits in the riverbed or the spreading of hard materials during floods. Levees, on the other hand, are embankments formed along the sides of a river to prevent flooding and are not formed by the deposition of materials during floods.

A positive movement occurs when there is a depression of land or a sea level rise. This will submerge the lands along the coast, drown' the valleys, and weaken the river's erosive power. The flow is checked, and large quantities of sediment will be dropped.

The correct answer is option 'C' - Both of them.

Explanation:

Statement 1: The flood plains of large rivers with their thick mantles of fine silt are some of the richest agricultural areas of the world.
The flood plains of large rivers are typically formed by the deposition of sediments such as silt, clay, and sand during floods. These sediments are rich in nutrients and make the soil very fertile. The fine silt in particular is known for its high fertility and ability to retain moisture. As a result, the flood plains of large rivers are highly suitable for agriculture and are considered some of the richest agricultural areas in the world. Farmers in these areas can grow a wide range of crops, including rice, wheat, maize, and vegetables. The fertility of the soil allows for high crop yields, making these areas economically important for food production.

Statement 2: They may support very dense populations and a chain of large cities may be strung along their banks.
The rich agricultural resources provided by the flood plains of large rivers often lead to the development of dense human settlements and the growth of cities. The fertile soil supports intensive agriculture, which in turn can support larger populations. The availability of food and water resources from the rivers facilitates the growth of settlements along their banks. These settlements may start as small villages, but as the population grows and agricultural production increases, they can evolve into larger towns and cities. Examples of large cities that have developed along the flood plains of rivers include Cairo along the Nile River, Dhaka along the Brahmaputra River, and Bangkok along the Chao Phraya River.

Conclusion:
Both statements 1 and 2 are correct. The flood plains of large rivers are indeed some of the richest agricultural areas in the world due to their fertile soil, and they often support dense populations and the growth of cities along their banks.

Lower or Plain Course of a River

The lower or plain course of a river is the final stage of its journey towards the sea. The following statements explain the characteristics of the lower course of a river:

Heavy with Debris: The river moving downstream across a broad, level plain is heavy with debris brought down from the upper course. This debris includes boulders, pebbles, and sand that have been eroded from the upper course of the river.

Lateral Corrasion: Vertical corrasion has almost ceased through lateral corrasion still goes on to erode its banks further. Lateral corrasion is the process by which a river erodes its banks through the sideways movement of water.

Deposition: The work of the river is mainly deposition, building up its bed and forming extensive flood plains. Deposition is the process by which a river drops the sediment it has been carrying, forming features such as sandbars, levees, and floodplains.

Conclusion

All of the above statements are correct. The lower or plain course of a river is characterized by the heavy deposition of sediment brought down from the upper course, erosion of banks through lateral corrasion, and the formation of extensive floodplains.

Explanation:
The correct statement is option 'A' which states that statement 1 is correct.

Statement 1: When a river reaches the sea, the fine materials it has not yet dropped are deposited at its mouth, forming a fan-shaped alluvial area called a Delta.

Explanation:
A river delta is a landform that forms at the mouth of a river where it flows into an ocean, sea, lake, or another river. Deltas are formed as a result of sediment deposition by the river as it reaches the sea. When a river flows into a body of water, it loses its energy and velocity, causing it to drop the sediments it was carrying. The fine materials such as silt, clay, and sand are deposited near the mouth of the river, forming a fan-shaped alluvial area called a delta. Deltas are often characterized by their rich fertile soil and are important areas for agriculture and wildlife.

Statement 2: Due to the obstruction caused by the deposited alluvium, the river may discharge its water through several channels called tributaries.

Explanation:
This statement is incorrect. Tributaries are not channels through which a river discharges its water. Instead, tributaries are smaller rivers or streams that flow into a larger river. They contribute their water to the main river, increasing its volume and flow. The main river, not the tributaries, is responsible for discharging its water into the sea or another body of water.

In summary, the correct statement is option 'A' which states that statement 1 is correct. Deltas are formed when a river reaches the sea and deposits its fine materials, forming a fan-shaped alluvial area. However, statement 2 is incorrect as tributaries are not channels through which a river discharges its water.