Bihar flooded despite rainfall deficit; Nepal isn’t the reason

Why in the News

Bihar has flooded in a season of deficit rainfall. The State received 601.1 mm of rain between 1 June and 8 September, 27% below normal, and the Disaster Management Department recorded 2,157 villages across 14 districts affected. The Water Resources Minister has said this year’s flood pattern differed from previous years, with the Ganga rising first rather than the rivers that enter Bihar from Nepal. Discharge at the Valmikinagar Barrage on the Gandak stayed below what officials had expected, and the flooding continued anyway. The explanation offered is a backwater effect, so the immediate cause sits downstream in the main river rather than upstream across the border.

What is a backwater effect?

1. How a tributary drains: A tributary can discharge into a main river only for as long as the water level in the main river stays below its own.
2. What happens when the main stem rises: A high stage in the main river holds the tributary’s water back and spreads it across the tributary’s own floodplain, with no additional rain falling there.

Why did Bihar flood on a rainfall deficit?

1. The seasonal shortfall: Rainfall from 1 June to 8 September was 601.1 mm, 27% below normal, and the deficit stood at 30% as late as 1 September.
2. The month ran the other way: Rainfall during September itself was 31% above normal, so the cumulative figure conceals the period when the flooding worsened.
3. Localised extremes: Individual rain events delivered 214.92 mm in East Champaran and 154.55 mm in Sitamarhi.
4. The recorded damage: By 9 September the Disaster Management Department reported 2,157 villages in 14 districts affected and about 40.51 lakh people hit.
5. Seasonal totals are the wrong measure: A flood is produced by the intensity and timing of rain and by upstream discharge, not by the season’s aggregate.

How was this year’s flood sequence different?

1. The usual order: The Bagmati, Kamla, Kosi and Gandak, which enter Bihar from Nepal, normally rise first, and the Ganga follows.
2. What happened instead: The Ganga became the first source of concern this year, which inverted the sequence the State’s flood response is built around.
3. The catchment is not local: The Ganga’s catchment extends far beyond Bihar, so it carries water generated by rainfall upstream, including in Uttar Pradesh.
4. The stated drivers: The Disaster Management Department’s Principal Secretary identified rainfall around the Allahabad and Varanasi region and the resulting downstream discharge as important factors, with discharge from neighbouring States a major factor for the other rivers too.

Why did opening the Valmikinagar Barrage not settle the Gandak?

1. The gates were opened early: When floods hit Nepal on 26 August, Bihar opened all 36 gates of the Valmikinagar Barrage on the Gandak, which was then below its normal levels.
2. The peak came in under expectation: Discharge at the barrage reached 1,50,200 cusecs (cubic feet per second, the volume of water passing a point each second) and then declined, below what officials had expected.
3. Flooding continued regardless: The Gandak and the Punpun could not drain once the Ganga had swelled, which is the backwater effect at work.
4. A second local input: The Punpun was also carrying heavy rainfall from Jharkhand.
5. A flood travels: A river flood is a moving event, so a peak recorded at one gauge is transferred downstream and the flooded area is far larger than the area that recorded the heaviest rain.

What do Bihar’s embankments do, and what do they not do?

1. The length built: The State has built more than 3,730 km of river embankments.
2. What they have protected: These structures have historically shielded around 3,600 sq km of land during floods.
3. The limit of the structure: Embankments do not remove the underlying vulnerability of one of India’s flattest and most sediment heavy alluvial landscapes.
4. Sediment raises the bed: The Ganga, Gandak, Kosi and Bagmati carry enormous quantities of sediment, and accumulation within a channel lifts the riverbed relative to the land beside it. Silt is a permanent condition of Bihar’s rivers rather than an event.

Why has the Farakka Barrage entered the flood argument?

1. The State’s contention: State leaders hold that the Farakka Barrage has trapped large volumes of silt along the Ganga over the five decades since it was built.
2. The claimed consequence: That accumulation has made the riverbed shallower, so even normal seasonal monsoon flows now spill over the banks and produce annual flooding across the plains.
3. A treaty deadline gives it timing: The 1996 India Bangladesh Farakka Treaty expires in December 2026, and demands in Bihar are for a review of the pact.

What in Bihar’s own geography keeps exposure high?

1. The rivers move: The Ganga, Gandak and Kosi constantly reshape their channels, so the land at risk is not fixed from one year to the next.
2. People live at the water’s edge: High population density means many communities are settled close to rivers, and a rise in level turns into an evacuation rather than an inconvenience.

Challenges to Bihar’s flood management

1. An embankment concentrates risk at its weakest point: A breach releases water at high velocity onto land that the structure had kept dry for decades, so the damage is deeper than an unprotected flood. Eg. The Kosi breach at Kusaha in 2008 shifted the river’s course and displaced over three million people in Bihar.
   The Fix: Hold a pre positioned stock of boulders and geobags at identified weak reaches before each monsoon rather than mobilising material after a breach.
2. Land behind the line cannot drain itself: An area sealed off from the river also loses the outlet for its own rainfall, so ground protected from flooding turns permanently waterlogged. Eg. Large tracts in the Kosi and Bagmati belts of north Bihar have gone out of cultivation from persistent waterlogging.
   The Fix: Build and maintain sluices and drainage channels through the embankment line with a fixed operating protocol for the monsoon months.
3. Flood moderation depends on storage that does not exist: Peak attenuation on the Kosi and the Gandak requires reservoirs upstream in Nepal that have never been constructed. Eg. A high dam at Barahkshetra on the Kosi has been under discussion since the 1950s without being built.
   The Fix: Separate real time data sharing and joint forecasting from the dam negotiation, so warning improves without waiting on construction.
4. Warnings are issued off levels already recorded: Forecasts rest on gauge readings at the moment of the peak, which leaves little lead time on terrain where water spreads sideways for tens of kilometres. Eg. A level based warning gives downstream districts only hours once an upstream gauge has crossed its danger mark.
   The Fix: Build district level inundation forecasts from upstream rainfall and barrage release data rather than from gauge readings alone.

Conclusion

Bihar’s flood risk is no longer set mainly by how much rain falls inside the State. It is set by the level of the main river the State has to drain into, and by channels whose beds have risen relative to the land beside them. The unresolved tension is that the structures protecting settled land also hold in the sediment that raises those beds, so each decade of protection shortens the next decade’s margin. What to watch is whether flood planning shifts from adding embankment length to sediment management, drainage behind the line and forecasting built on upstream data.

Back2Basics: Farakka Barrage

1. What it is and where: A barrage on the Ganga in Murshidabad district of West Bengal, commissioned in 1975, a short distance upstream of the border with Bangladesh.
2. Why it was built: It diverts a part of the Ganga’s flow into a feeder canal to the Bhagirathi and Hooghly, to flush silt and maintain navigability for the port of Kolkata.
3. A barrage, not a dam: It regulates and diverts flow through gates rather than impounding a large storage reservoir behind it.
4. The water sharing arrangement: An agreement between India and Bangladesh shares the dry season flow measured at the barrage in ten day cycles between 1 January and 31 May.

Matching Previous Year Question

“[2024, GS3, 15 marks] What is disaster resilience? How is it determined? Describe various elements of a resilience framework. Also mention the global targets of the Sendai Framework for Disaster Risk Reduction (2015-2030).”