Assertion (A) : The frequency of floods in North Indian plains has increased during the last couple of decades. Reason (R) : There has been reduction in the depth of river valleys due to deposition of silt.

The assertion is correct: multiple studies and assessments report increasing frequency and magnitude of extreme rainfall and flood events over the Indo‑Gangetic/North Indian plains in recent decades, linking these changes to enhanced extreme precipitation trends [1] and observed rise in inundation incidents across northern states in recent decades [2]. The reason is also valid: rivers carrying large sediment loads deposit silt in lower reaches, causing channel aggradation and build‑up of the floodplain which reduces effective channel depth and elevates flood risk during high flows [3]. Anthropogenic factors such as encroachment and construction in floodplains further amplify flood impacts by restricting natural flood storage and conveyance [4].

Sources

1. [2] INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 6: Natural Hazards and Disasters > Floods > p. 62
2. [3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > Chambal Ravines > p. 14
3. [4] https://www.niti.gov.in/sites/default/files/2021-03/Flood-Report.pdf