Nepal Flash Flood: Why Bihar Is on Alert as Gandak and Kosi River Levels Rise

Patna, 27th August 2026: Bihar has been placed on alert after a devastating flash flood originating near the Nepal-Tibet border swept through parts of Nepal, raising concerns over rising water levels in the Gandak and Kosi river systems downstream.

The disaster struck Nepal’s Rasuwa district on Wednesday morning after a sudden surge of water entered the Bhote Koshi River. The flood devastated settlements including Timure and Syaphrubesi, washed away bridges and roads and damaged several hydropower projects. Nepalese authorities have confirmed 95 deaths, while hundreds of people remain unaccounted for.

The disaster has also triggered concerns in Bihar because the rivers affected in Nepal are connected to river systems that flow into the state.

Why is Bihar at risk?
The potential risk to Bihar is primarily linked to the Trishuli-Gandak and Bhote Koshi-Kosi river systems.

The Trishuli flows south through Nepal before joining the Kali Gandaki near Devghat. The combined river is known as the Narayani and eventually enters India near Valmikinagar in West Champaran, where it is known as the Gandak.

Any significant increase in discharge through the Trishuli-Narayani system can therefore affect downstream areas of Bihar. Districts that could face increased pressure include West Champaran, East Champaran, Gopalganj, Saran and Muzaffarpur, particularly low-lying and diara areas.
The Bhote Koshi, meanwhile, joins the larger Sunkoshi river system, which forms part of the Sapta Koshi. The Kosi enters India near the Bhimnagar barrage and flows through Bihar before joining the Ganga near Kursela in Katihar.

A major increase in water flowing through the Bhote Koshi could therefore add pressure to the wider Kosi river system, with Supaul, Saharsa, Madhepura and Khagaria among the districts that could be vulnerable.
However, the extent of any downstream impact will depend on the volume and duration of the water surge, river levels and conditions along the river systems. It would be premature to compare the current situation with the catastrophic 2008 Kosi floods.

What caused the flash flood in Nepal?

The exact cause of the disaster is still being investigated.
Initial scientific assessments point to a major ice-and-rock avalanche or rockslide near the Nepal-Tibet border that blocked the Lhende River for some time. When the natural obstruction gave way, a large volume of water was released suddenly, producing a flash-flood-like surge.

Experts are also examining the possibility of a glacial lake outburst flood (GLOF), but that explanation has not been conclusively established. Recent assessments have linked the flooding to an ice-rock avalanche, while Nepalese authorities have also reported that the disaster was not caused by heavy rainfall in Rasuwa.

A 4.4-magnitude earthquake was also reported in the Tibet region shortly before the flooding, and authorities are examining whether the tremor contributed to the geological event.

Large-scale destruction in Nepal

The flash flood swept through Rasuwa and neighbouring districts, destroying homes, roads and bridges.

Nepal’s authorities have reported damage to at least 19 motorable bridges and around 40 kilometres of roads. Several hydropower projects have also been damaged.

The 42-km road connecting Betrawati with the Rasuwagadhi border crossing was severely damaged, disrupting an important route towards the Tibet border.

The flood also affected the Rasuwa settlements of Timure, Syaphrubesi, Mailung, Haku Besi, Salletar, Shantibazar, Pairebesi and other areas before moving downstream towards Nuwakot, Dhading and other districts.

The Nepal Tourism Board has reported hundreds of travellers unaccounted for, including foreign nationals. Indian nationals are among those reported missing.

Bihar government steps up preparedness

The Bihar government has activated its flood preparedness machinery following the developments in Nepal.

Chief Minister Samrat Choudhary reviewed the situation with senior officials from the Chief Secretary’s office, the Disaster Management Department and the Water Resources Department.

Deputy Chief Minister and Water Resources Minister Vijay Kumar Choudhary appealed to residents to remain alert but not panic. He said the next 24 hours would be important for monitoring the situation.
The government has increased the deployment of teams for flood relief and rescue operations and has arranged essential relief material.

The Centre has also assured support to Bihar. Union Home Minister Amit Shah spoke with the chief ministers of Bihar and Uttar Pradesh and assured assistance, while additional NDRF teams were placed on alert for the border areas.

Valmikinagar barrage on high alert

The Valmikinagar Gandak Barrage in West Champaran has been placed under close watch as authorities monitor the rising water levels and possible increase in pressure.

All 36 gates of the barrage have been opened to regulate the flow, according to the information provided by the state authorities.
Officials have also been asked to remain on duty, with leave cancelled for personnel involved in monitoring and flood management over the coming days.

People living in low-lying areas and settlements inside or near embankments are being alerted through public-address systems and advised to move to safer locations if required.

The Water Resources Department and Disaster Management Department are monitoring the situation through emergency control rooms.

Is another 2008-like Kosi flood possible?

The present situation is serious, but there is no basis at this stage to suggest that Bihar is heading for a repeat of the 2008 Kosi disaster.
In 2008, the Kosi breached its embankment at Kusaha in Nepal and shifted towards an old channel, causing widespread flooding in Bihar. More than three million people were affected in what became one of the state’s worst flood disasters.

The current Nepal disaster, by contrast, has been associated with a sudden geological event and a flash flood along the existing river system. There is no indication that the Kosi has changed its course in the manner seen in 2008.

That distinction is important when assessing the immediate risk to Bihar.

Why Nepal’s rivers are a recurring flood concern for Bihar

Bihar’s geography makes the state particularly vulnerable to floods originating in Nepal.

Nepal’s Himalayan and hill regions receive significant rainfall and contain the headwaters of several rivers that eventually flow into Bihar, including the Kosi, Gandak, Bagmati, Kamla-Balan and Mahananda systems.

Because Nepal’s terrain is considerably higher than the plains of Bihar, water flows rapidly downstream during periods of heavy rainfall or sudden increases in river discharge.

The absence of sufficient large-scale storage infrastructure in the upper reaches also remains a longstanding concern in flood management.

High dam proposal remains unresolved

The proposal for a high dam on the Sapta Kosi to provide flood control and other benefits has been discussed between India and Nepal for more than a century.

Discussions on a major Kosi dam date back to the late 19th century. A joint project office was subsequently established in Nepal to examine the feasibility of the proposed project, but a final agreement on construction has remained elusive.

The issue has again gained political attention amid the latest flood threat.
On August 21, Bihar Chief Minister Samrat Choudhary held discussions with Union Finance Minister Nirmala Sitharaman and External Affairs Minister S. Jaishankar on flood-related issues.

Following the meeting, the Centre directed the Water Resources Ministry to release funds for the first phase of the Kosi-Mechi project and move ahead with technical approval for the second phase.

Choudhary has also said that a detailed project report for a high dam on the Kosi should be prepared soon. JD(U) leader Sanjay Jha has described a high dam in Nepal as a long-term solution and said the DPR is expected by 2028.

For now, Bihar authorities are focusing on the immediate threat: monitoring water levels in the Gandak and Kosi systems, strengthening rescue preparedness and ensuring residents in vulnerable areas receive timely warnings.