The correct option is (a).
Explanation
The rivers originating from the Himalayas pass through three distinct courses: the upper course (mountainous), the middle course (plains), and the lower course (near the delta). The physiography of the Northern Plains significantly influences the behavior of these rivers.
- Statement 1 is Correct: As the rivers enter the Northern Plains and progress towards the sea (lower course), the gradient or slope of the land becomes extremely gentle. This reduction in slope causes a significant decrease in the velocity of the river water compared to the upper and middle courses.
- Statement 2 is Incorrect: The decrease in river velocity in the lower course reduces the water's capacity to carry sediments. Consequently, the heavy load of silt and debris settles down. This process leads to the formation of various depositional features such as riverine islands (e.g., Majuli in the Brahmaputra), sandbars, and deltas, rather than preventing them.
- Statement 3 is Incorrect: Due to the extensive deposition of silt, the riverbed rises, and the water flow is obstructed. To bypass these obstructions, the main river splits into numerous smaller channels. These channels are known as distributaries because they distribute water away from the main river. Tributaries are smaller streams that join the main river to add water, typically found in the upper and middle courses.
Key Takeaway: In the lower course of a river, the gentle slope reduces velocity, leading to heavy sediment deposition. This results in the formation of distributaries and depositional landforms like deltas and riverine islands.