Why can floods increase when the bed of a Himalayan river becomes shallow?

Correct answer: A shallow bed can force the river to spread even with less extra water

A river channel becomes shallower when sediment accumulates on its bed. This reduces the cross-sectional space available for water. During rainfall or a period of high discharge, the increased volume may not fit safely within the shallow channel. Water can then rise to the banks and spread across nearby low-lying land. Thus, a shallow bed can increase flood risk even when the additional water is not exceptionally large. Sediment deposition and reduced channel capacity are the important ideas.

Option A is correct because it connects a shallow bed with the spreading of water. The statement does not mean that every shallow river floods immediately; rather, shallow conditions make flooding more likely when discharge rises. Options B, C, and D are unrelated or impossible. A shallow bed does not dry the river, stop the sea, or turn the river into a volcano. In geographical reasoning, remember the sequence: more sediment in the bed → less channel capacity → higher water level and possible overflow.