Gandak Floods: Less Water, Higher Level, Why? | CLAT Explainer

VIDEO EXPLAINER | 10 OCTOBER 2026

In the last days of September 2026, the Gandak, a Himalayan tributary of the Ganga, broke its own all-time record. At the Bagaha gauge in West Champaran, the river touched 91.25 metres, which is 35 centimetres above the previous highest flood level of 90.90 metres, set on 29 September 2024. Records fell at four gauge sites in all. Embankments were breached at several points, dozens of villages went under water, and Indian Air Force helicopters air-dropped relief packets. This explainer covers the cause, the river’s course, a surprising detail in the data, and the India–Nepal treaty behind the Gandak barrage.

What happened

The figures come from the Bihar Water Resources Department, as reported by news agencies. Up to noon on 30 September, new records were set at four gauges: Bagaha (91.25 m), Dumariaghat (64.64 m), Rewaghat (55.55 m) and Lalganj (52.19 m).

On the night of 28 to 29 September, the left-bank Champaran embankment was breached at Khairatwa and Phuliakhad; later reports added two more breaches, for four within about ten hours. The right-bank Saran embankment was also damaged, and an embankment was damaged in Kushinagar in Uttar Pradesh. By 3 October, the department counted seven major breaches in the Gandak embankment. The State sought the Air Force’s help, and helicopters dropped dry-ration packets for about three days before boats took over. Reports of deaths and of the number of people affected conflict with one another, so we do not give a figure here.

Why: rain in Nepal

The trigger was torrential rain in Nepal’s Lumbini and Gandaki provinces from 24 to 27 September 2026, which caused landslides and pushed the river to record levels in both countries. In Nepal, the Devghat gauge reached 11.94 metres on 27 September, the highest since measurements began in the 1960s. NASA’s Earth Observatory published satellite images of the flooding on 2 October 2026, comparing the river on 20 September (before) with 29 September (during).

The river’s course

The Kali Gandaki rises in the Nepal–Tibet Himalaya, in Mustang. Lower down in Nepal it is called the Narayani, after the Trishuli joins it. It enters India near Triveni / Valmikinagar in West Champaran and joins the Ganga at Sonepur, opposite Patna, near Hajipur. Because most of its catchment lies in Nepal, heavy rain across the border drives the floods downstream in India.

The puzzle: less water, higher level

Here is the most interesting detail. On 28 September, the Valmikinagar barrage released 5,43,500 cusecs. In 2024, the peak release was higher, at 5,62,500 cusecs. So less water came through in 2026, yet the level at Bagaha went higher (91.25 m against 90.90 m).

The general mechanism that explains such floods in the region is silt. Young, fragile Himalayan geology and intense monsoon rain cause heavy erosion, so these rivers carry a large silt load. When embankments confine a river, the silt settles between them and raises the riverbed. A higher bed means the same, or even a smaller, volume of water stands higher, and when an embankment breaks, water spreads over a wide area. Think of sand settling at the bottom of a bucket: the more sand, the less water it takes to overflow. This is the general reason; it is not a measured cause of the 2026 record.

The India–Nepal Gandak Agreement

The Gandak Agreement between India and Nepal was signed at Kathmandu on 4 December 1959, came into force on signature, and was amended in 1964. It covers a barrage, canal head regulators and canals for irrigation and power for both countries, built at India’s cost; Nepal gets irrigation water and a share of the power. The Gandak barrage at Valmikinagar straddles the border and has been operated by India.

The Kosi comparison

The Gandak is not the only Himalayan river with this problem. The Kosi, called the “Sorrow of Bihar”, carries one of the heaviest silt loads in the world and is known for shifting its course. In August 2008, it breached its embankment at Kusaha in Nepal, affecting about 2.7 million people. India and Nepal signed the Kosi Agreement in 1954. For any exam, the lesson is the same: embankments protect, but they can also trap silt and raise the stakes when they fail.

Sources

PTI (via ThePrint) and ANI reports of 29 to 30 Sep 2026 quoting the Bihar Water Resources Department; Patna Press and Daily Pioneer (Sep–Oct 2026) on barrage releases and breaches; ETV Bharat and Telangana Today (Oct 2026) on later breaches and relief; NASA Earth Observatory, “Rains Swamp the Gandak River” (2 Oct 2026); the India–Nepal Gandak Agreement text (FAO FAOLEX; International Water Law Project); India Water Portal on the 2008 Kosi flood.