Why does encroachment along river banks increase disaster risk?

Correct answer: Because construction occurs in the river’s spread zone

A river channel and its floodplain need space to carry and temporarily spread excess water during heavy rain. When people build houses, roads, walls, or other structures in this natural spread zone, the water loses room and its flow may be obstructed. Drainage can become slower, water levels can rise locally, and nearby people and property face greater flood damage.

Option A is correct because it identifies construction in the river’s spread or flood zone as the cause of increased risk. A calm current does not explain a rise in disaster danger, increased vegetation generally does not create this problem, and water treatment is unrelated to bank encroachment. The issue is not simply that construction is near water; it is that it occupies space needed during floods. The supplied answer is accurate.