Bihar floods despite a 27% rain deficit, and the Ganga, not Nepal, is behind it
How can a State short of rain be under water? Look downstream at the Ganga and Farakka, not north at Nepal.
Published 11 September 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
Floods in Bihar had affected about 40.51 lakh people in 2,157 villages across 14 districts by 9 September 2026, even though the State recorded a 27% rainfall deficit between 1 June and 8 September. The Hindu reports that this year's pattern was unusual. In most years, the rivers that flow in from Nepal, such as the Bagmati, Kamla, Kosi and Gandak, swell first and flood north Bihar. This time the Ganga rose first, fed by heavy rain upstream around Allahabad and Varanasi and by discharge from neighbouring States. Heavy, localised rain within Bihar in September, 31% above normal, made things worse.
The mechanism is the backwater effect. When the Ganga runs high, its tributaries, such as the Gandak and the Punpun, cannot drain into it. Their water backs up and spills over the land. The report also points to the Farakka Barrage in West Bengal, which became operational in 1975 to divert Ganga water into the Hooghly and keep Kolkata port navigable. Critics say the barrage traps large amounts of silt upstream, which has made the Ganga's bed in Bihar shallower and increased flood frequency. Bihar has more than 3,730 km of river embankments, but these do not remove the basic flood risk of a sediment-heavy alluvial plain.
The timing gives the issue a diplomatic edge. The Ganga water-sharing treaty between India and Bangladesh, signed on 12 December 1996 for 30 years, expires in December 2026, and there are demands in Bihar that it be reviewed. The treaty governs how Ganga water at Farakka is shared in the dry season. Any renegotiation must balance Bangladesh's lean-season share, West Bengal's need for water in the Hooghly and Bihar's concern over silt and floods. The report's larger point is that Bihar's floods cannot be blamed only on Nepal's rivers: the Ganga's own flow, silt and structures downstream shape the risk.
Prelims facts
- By 9 September 2026, floods had affected about 40.51 lakh people in 2,157 villages across 14 Bihar districts despite a 27% rain deficit from 1 June to 8 September.
- In 2026 the Ganga rose before the Nepal-fed rivers (Bagmati, Kamla, Kosi, Gandak), causing a backwater effect on tributaries such as the Gandak and the Punpun.
- The Farakka Barrage, on the Ganga in Murshidabad district of West Bengal, became operational in 1975 to divert water to the Hooghly for Kolkata port.
- The India-Bangladesh Ganga water treaty was signed on 12 December 1996 by H.D. Deve Gowda and Sheikh Hasina for 30 years and expires in December 2026.
Quick recall
- How large was Bihar's rainfall deficit from 1 June to 8 September 2026?
- 27%.
- How many people had Bihar's floods affected by 9 September 2026?
- About 40.51 lakh, in 2,157 villages across 14 districts.
- What is the backwater effect?
- A rise in a tributary's water level because the main river it drains into is running high.
- In which district is the Farakka Barrage?
- Murshidabad district, West Bengal.
- When did the Farakka Barrage become operational?
- 1975.
- Who signed the India-Bangladesh Ganga water treaty, and when?
- H.D. Deve Gowda and Sheikh Hasina, on 12 December 1996.
- For how long was the Ganga water treaty signed?
- 30 years; it expires in December 2026.
- How long is Bihar's network of river embankments?
- Over 3,730 km.
Prelims practice question
With reference to the Farakka Barrage, which one of the following is correct?
- It is in Murshidabad district of West Bengal and was built mainly to divert Ganga water into the Hooghly to keep Kolkata port navigable.
- It is in Bhagalpur district of Bihar and was built mainly to control floods of the Kosi.
- It is in Malda district of West Bengal and was built mainly for hydroelectric power.
- It is on the Brahmaputra and regulates water sharing with Bangladesh.
Show answer
Answer: (a) It is in Murshidabad district of West Bengal and was built mainly to divert Ganga water into the Hooghly to keep Kolkata port navigable.. The Farakka Barrage stands across the Ganga in Murshidabad district, West Bengal. It became operational in 1975 and diverts water through a feeder canal into the Bhagirathi-Hooghly to flush silt from Kolkata port. It is not a Kosi flood-control or hydropower project, and it is on the Ganga, not the Brahmaputra.
Use this in UPSC Mains: previous-year questions
Recurring theme: River systems, floods and disaster management in the Ganga plains
- How to use this
Bihar's 2026 floods amid a rain deficit show how barrages, embankments and silt, not rainfall alone, now decide how monsoon rain becomes floods.
- Floods affected about 40.51 lakh people in 2,157 villages across 14 Bihar districts by 9 September 2026 despite a 27% rainfall deficit from 1 June to 8 September.
- Critics say the Farakka Barrage (operational 1975) traps silt upstream, making the Ganga bed in Bihar shallower and raising flood frequency.
- Bihar's more than 3,730 km of embankments confine rivers but raise beds through silt deposition, and breaches cause sudden floods.
- How to use this
River structures in Bihar show how barrages and embankments create downstream and upstream hazards, supporting the causes part of the answer.
- Critics say the Farakka Barrage, operational since 1975 to divert Ganga water to the Hooghly, traps silt upstream, raising flood frequency in Bihar.
- Bihar's more than 3,730 km of embankments raise river beds through silt deposition; the 2008 Kosi embankment breach shows how such structures can fail suddenly.
- Policy point: manage sediment at and above Farakka and strengthen flood forecasting on the Ganga main stem, not only on Nepal-fed rivers.
The Bhojpur region lies in Bihar's Ganga plain; knowing its monsoon winds and rivers helps explain how rain upstream and within Bihar drives floods like those of 2026.
Mains practice question
Floods in Bihar in a rain-deficit year show that flood risk is shaped as much by river behaviour and structures as by rainfall. Discuss with reference to the backwater effect and the Farakka Barrage. (250 words)
Model answer
In 2026 Bihar recorded a 27% rainfall deficit (1 June to 8 September), yet floods affected about 40.51 lakh people in 14 districts by 9 September. The paradox shows that floods are a river-system problem, not only a rainfall problem.
Role of river behaviour
- Upstream rain: heavy rain around Allahabad and Varanasi raised the Ganga before Nepal-fed rivers rose.
- Backwater effect: a high Ganga blocked outflow of tributaries like the Gandak and the Punpun, which spilled over.
- Local bursts: September rain in Bihar was 31% above normal.
Role of structures
- Farakka Barrage (1975): diverts water to the Hooghly for Kolkata port; critics say it traps silt upstream, making the Ganga bed in Bihar shallower.
- Embankments: over 3,730 km confine rivers but raise beds through silt deposition, and breaches cause sudden floods, as in the 2008 Kosi breach.
Policy implications
- Treat the Ganga basin as one unit, including sediment management at and above Farakka.
- Use the review of the 1996 India-Bangladesh treaty, which expires in December 2026, to address silt and flood concerns alongside dry-season sharing.
- Strengthen flood forecasting on the main stem, not only on Nepal-fed rivers.
- Restore wetlands and floodplains to store excess water, and follow the NDMA flood guidelines on zoning.
Balancing interests
- Bangladesh's lean-season needs and Kolkata port's navigability must be weighed against Bihar's flood risk.
Bihar's floods call for managing water, silt and structures together across the whole basin, not just blaming heavy rain in Nepal.
The basics
Why this matters
Bihar is among India's most flood-prone States, and we usually blame heavy rain in Nepal. In 2026 the State had a 27% rain deficit from 1 June to 8 September, yet about 40.51 lakh people in 14 districts were hit by floods by 9 September. To understand why, you need three ideas: how Bihar's rivers are arranged, the Backwater effect, and what the Farakka Barrage does to silt.
Bihar's river layout
The Ganga flows west to east across Bihar. From the north, rivers that rise in or pass through Nepal, such as the Gandak, Bagmati, Kamla and Kosi, drop steeply onto the plain carrying heavy silt. From the south, smaller rivers such as the Punpun join the Ganga. All of them must drain into one main river, which then flows on to Farakka in West Bengal.
- 1GangaThe main river that every tributary must drain into
- 2Nepal-fed north-bank riversGandak, Bagmati, Kamla, Kosi: steep, silt-laden, usually the first to flood
- 3South-bank riversThe Punpun and others that join the Ganga from the south
- 4Farakka BarrageDownstream structure in West Bengal that diverts water and traps silt
How a full river floods its tributaries
When the main river is high, it acts like a closed door for tributaries. Their water slows, backs up and spreads over the land. This year the Ganga rose first because of heavy rain upstream around Allahabad and Varanasi, so the door closed early.
- 1Upstream rainHeavy rain around Allahabad and Varanasi and inflow from neighbouring States raise the Ganga
- 2Ganga rises firstUnlike most years, the main river swells before the Nepal-fed rivers
- 3BackwaterTributaries such as the Gandak and Punpun cannot drain and back up
- 4Local downpoursSeptember rain in Bihar, 31% above normal, adds water that has nowhere to go
- 5Flooding2,157 villages in 14 districts are affected by 9 September
The silt problem and the treaty
The Farakka Barrage, operational since 1975, traps silt upstream, and critics link it to a shallower Ganga bed in Bihar. Bihar's 3,730 km of River embankments add their own risks. The Ganga Water Treaty, 1996 with Bangladesh expires in December 2026, and Bihar wants its concerns on the table.
- 1962Construction of the Farakka Barrage begins
- 1975The barrage becomes operational
- 12 December 1996India and Bangladesh sign the 30-year Ganga water-sharing treaty
- September 2026Bihar floods despite a rain deficit; demands to review the treaty
- December 2026The treaty is due to expire
Go deeper
In one line: Bihar flooded in a rain-deficit year because the Ganga rose early and blocked its tributaries, a problem worsened by silt trapped upstream of the Farakka Barrage.
Why it matters for UPSC
The story ties physical geography (river systems, alluvial plains) to disaster management and to India-Bangladesh relations, since the Ganga treaty expires in December 2026.
The core idea
Floods are not only about rain. When a main river is high, the Backwater effect stops tributaries from draining. The Farakka Barrage traps silt upstream, and critics say this makes the Ganga shallower in Bihar. River embankments confine rivers but can raise their beds and fail suddenly. The Ganga Water Treaty, 1996 now comes up for renewal, bringing these concerns into diplomacy.
Numbers and dates to remember
- 27% rain deficit in Bihar, 1 June to 8 September 2026.
- About 40.51 lakh people, 2,157 villages, 14 districts affected by 9 September.
- September rain in Bihar 31% above normal.
- Over 3,730 km of embankments in Bihar.
- Farakka Barrage operational in 1975; treaty signed 12 December 1996 for 30 years.
Where to go next
- Backwater effect: why a full river floods its tributaries.
- Farakka Barrage: the structure at the centre of the silt debate.
- Ganga Water Treaty, 1996: the India-Bangladesh pact that expires in December 2026.
- River embankments: the flood defence that can raise the risk it guards against.
Go deeper: who pays for a barrage's silt?
Bihar's case. Bihar's leaders have long argued that the Farakka Barrage has slowed the Ganga and let silt pile up upstream, raising the riverbed and worsening floods. The 2026 pattern, where the main river rose first and the Backwater effect did the damage, strengthens the argument that the Ganga's own condition matters as much as Nepal's rivers.
West Bengal's and Kolkata's case. The barrage exists to push water into the Hooghly and keep Kolkata port usable. Removing or changing it would hurt the port and the river's water supply.
Bangladesh's case. Under the Ganga Water Treaty, 1996, Bangladesh depends on assured dry-season flows at Farakka. Any renegotiation that raises India's withdrawals, or changes how the barrage is run, will face resistance there.
The engineering debate. Embankments have been Bihar's main defence, but River embankments trap silt inside the channel and can fail catastrophically, as in the 2008 Kosi breach. Many experts now argue for room for rivers: floodplain zoning, wetland storage, sediment management and better forecasting on the main stem.
What a good renewal could do. The treaty review is a chance to add sediment data sharing, joint monitoring and flood forecasting to a pact that so far mainly deals with dry-season water sharing.
Backwater effect
Why a full river floods its tributaries
In one line: The backwater effect is the rise in water level along a tributary when the main river it flows into is running high.
How it works
A tributary drains because its water level is higher than the main river's at the meeting point. If the main river rises, that difference shrinks or reverses. The tributary slows, water piles up behind the confluence, and it spills over banks far from the main river. The same effect occurs behind dams and barrages, where a reservoir raises water levels upstream.
Why it is in the news
In 2026 heavy upstream rain raised the Ganga before the Nepal-fed rivers swelled. Tributaries such as the Gandak and the Punpun could not drain, so Bihar flooded despite a 27% rain deficit.
Where to go next
Farakka Barrage
The structure at the centre of the silt debate
In one line: The Farakka Barrage is a barrage across the Ganga in Murshidabad district of West Bengal that diverts water into the Hooghly.
Purpose and history
Construction began in 1962 and the barrage became operational in 1975. A feeder canal carries water from the Ganga to the Bhagirathi-Hooghly, to flush out silt deposited at Kolkata port and keep it navigable.
The criticism
A barrage slows the river, and slow water drops its silt. Large volumes of sediment are trapped upstream of Farakka. Critics, especially in Bihar, link this to a shallower Ganga bed and more frequent floods upstream. Downstream, Bangladesh has long complained about reduced dry-season flows.
Where to go next
Ganga Water Treaty, 1996
The India-Bangladesh pact that expires in December 2026
In one line: The Ganga Water Treaty is a 30-year agreement between India and Bangladesh on sharing Ganga water at Farakka in the dry season.
Key terms
It was signed on 12 December 1996 by Prime Ministers H.D. Deve Gowda and Sheikh Hasina. The sharing formula depends on flow at Farakka: at 70,000 cusecs or less, each side gets half; between 70,000 and 75,000 cusecs, Bangladesh gets 35,000 cusecs and India the balance; at 75,000 cusecs or more, India gets 40,000 cusecs and Bangladesh the balance.
Why it is in the news
The treaty expires in December 2026. Bihar wants its flood and silt concerns heard, West Bengal wants water for the Hooghly, and Bangladesh wants assured lean-season flows.
Where to go next
River embankments
The flood defence that can raise the risk it guards against
In one line: Embankments are earthen walls built along rivers to keep floodwater within the channel.
Why they help and hurt
Embankments protect towns and fields from moderate floods. But silt that would have spread over the floodplain settles inside the channel, raising the riverbed. Over time the river flows higher than the land around it, so a breach releases water with great force. The 2008 breach of the Kosi embankment at Kusaha in Nepal is the best-known example.
Bihar's case
Bihar has over 3,730 km of embankments. The 2026 floods show that they cannot remove the risk on a sediment-heavy alluvial plain, especially when the Ganga itself is high.
Where to go next
Take the 11 September 2026 quiz: 54 Prelims-style questions with answers