Environment · 21 Jul 2026

Yamuna floodplain formative discharge

Which one of the following statements, based on the 200-year hydrogeomorphic study of the Yamuna in Delhi, is correct?

AThe July 2023 flood reached Delhi's highest-ever recorded water level despite carrying a lower peak discharge than the 1978 flood.
BThe Yamuna's channel in Delhi has widened by 68% over the last two centuries due to increased monsoon rainfall.
CNearly 90% of the Yamuna's flow is diverted downstream of Delhi at the Okhla Barrage, depleting the river before it reaches the city.
DSediment deposit area within the Yamuna's channel increased from about 4 sq km in 1985 to 20 sq km by 2020 due to reduced formative discharge.
This question is based on: Delhi's "Natural" Floods Are Actually a Century of Engineering Decisions
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About this question

Why in news

A Delhi University-IISER Bhopal study published in the Journal of the Geological Society of India traces 200 years of Yamuna channel narrowing and floodplain disconnection, directly linking this to the record-breaking July 2023 Delhi flood.

Why for UPSC

UPSC frequently tests whether an aspirant can identify a counter-intuitive but well-evidenced causal claim (lower discharge, higher flood level) amid several plausible-sounding but factually reversed distractors.

Prelims summary

The Yamuna's Delhi channel narrowed 68% over 200 years, with sediment deposits shrinking from 20 sq km (1985) to 4 sq km (2020) and ~90% of flow diverted upstream at Hathnikund - explaining why 2023's flood peaked higher than 1978's despite less discharge.

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