Floods

Story hook

It is 18 August 2008, late evening. 80 km north of Birpur, Bihar, the Kosi River — historically called the "Sorrow of Bihar" — breaches an eastern afflux bund at the Kusaha point in Nepal. The river, which had been flowing on its western channel since 1963, abruptly shifts back 120 km eastward to an old paleochannel. In 72 hours, 30 lakh people in Saharsa, Madhepura, Supaul, Araria, Purnia are inundated. 250 villages disappear. The Indo-Gangetic plain witnesses one of the largest peacetime evacuations in Indian history — 30 lakh displaced.

By the time the waters recede in October, ~250 dead, ~30 lakh displaced, 3.5 lakh hectares of cropland destroyed. Damage: ₹1,000 crore. Bihar State government flounders; PM Manmohan Singh declares national calamity.

Why? The Kosi has the largest sediment load per square km of catchment in the world (~1,915 tonnes/sq km/year). Its bed rises faster than its banks can be raised. Embankments fail every 5-10 years. In 1954, the Kosi Barrage at Birpur was the engineering solution. By 2008, the river had silted up above the floodplain — engineering gravity-defying. Embanked flooding is a unique Indian flood disaster: when an embanked river breaches, the flood is catastrophic because the river-bed is above the surrounding plain.

This unit covers river flooding, flash floods, urban floods, the Central Water Commission (CWC), NDMA flood guidelines, and the climate change-flood nexus.

Why this matters for UPSC

Floods are India's most frequent and destructive natural disaster. They affect 75 million people annually on average, cause ₹1,800 crore + losses every year. Prelims tests CWC, flood forecasting stations, embankments. Mains demands the flood- management policy debate: embankments vs catchment management, reservoir operation, urban drainage. Interview boards probe Wayanad, Sikkim GLOF, Chennai 2015 — recent cases.