Patna: “The situation is under control, but the danger is not over yet.”
Bihar Chief Minister Samrat Choudhary’s assessment after the recent disaster in Nepal has offered temporary relief to people living in the state’s vulnerable areas, while also underlining the need for continued vigilance.
The key question now is whether Nepal could witness another major flood or landslide-related event and, if that happens, how much impact it could have on Bihar.
The answer depends largely on developments in the Himalayan region, rainfall over Nepal and the behaviour of rivers such as the Gandak, Kosi and Ganga, which carry water downstream into Bihar.
Could Nepal witness another flood?
Experts have not ruled out the possibility of further flooding or debris flows in parts of Nepal.
Scientists have warned that unstable mountain slopes and partially collapsed glacial formations could create conditions for fresh debris flows in the coming days. Nepal’s Home Minister Sudan Gurung has also said that the Lhende River has not yet been completely cleared, indicating that the risk in the affected area has not disappeared.
The International Centre for Integrated Mountain Development (ICIMOD) has said that persistent cloud cover has made satellite monitoring of the affected region difficult. Scientists are continuing to monitor glacial lakes and other high-risk areas.
China has also reported a potentially dangerous situation downstream. According to China’s Ministry of Water Resources, a large barrier lake has formed near the confluence of the Chotchen and Purupu Tsangpo rivers.
A report by the Global Times said that around 2 million cubic metres of water had accumulated in the lake by Thursday morning, with water beginning to flow out. China Central Television (CCTV) reported that another 3 million cubic metres could enter the lake over the following three days, raising concerns about the stability of the barrier.
Chinese authorities are monitoring the lake and conducting flood simulations to assess the possible consequences of a breach, while preparing emergency response and rescue measures.
The Chotchen and Purupu rivers originate in Tibet and merge before entering Nepal, where the river is known as the Bhote Koshi. The Bhote Koshi is a major upper tributary of the Trishuli River.
However, Kathmandu University climate researcher and professor Rijan Bhakta Kayastha has cautioned against drawing premature conclusions.
Kayastha said there had initially been concern that another large lake could form upstream, but there was not yet enough evidence to confirm the existence of such a lake.
He also warned that the broader risk remains because rising temperatures can contribute to glacier melt, the destabilisation of ice and rocks and an increased possibility of avalanches in the Himalayas. However, he said it is not possible to predict precisely where the next event could occur.
Why does a glacier-related disaster in Nepal threaten Bihar?
The geography of the Himalayan river system explains why developments in Nepal can have a direct bearing on Bihar.
Several rivers originating in or passing through Nepal eventually enter Bihar or join major river systems that flow into the state.
Route 1: Narayani-Gandak river system
The Trishuli River, one of the rivers associated with the recent disaster in Nepal, flows through the country’s mountainous region before joining the Kali Gandaki at Devghat. The combined river is known as the Narayani in Nepal.
The Narayani enters Bihar near West Champaran, where the river is known as the Gandak.
The Gandak then flows through parts of East Champaran and Gopalganj before passing through the wider Saran region and reaching Hajipur, where it meets the Ganga.
Any significant increase in upstream water flow can therefore affect several districts along the Gandak system.
Route 2: Bhote Koshi-Sapta Koshi system
The Bhote Koshi flows southwards through Nepal and joins the Sunkoshi and other rivers that form the Sapta Koshi system.
The Koshi enters Bihar through the Kosi Barrage at Bhimnagar, near Birpur in Supaul district.
Further downstream, the river system is influenced by tributaries including the Bagmati and Kamla before eventually meeting the Ganga near Kursela in Katihar district.
This makes districts such as Supaul, Saharsa, Madhepura and Khagaria particularly sensitive to major changes in the river system.
Route 3: Nepal’s western rivers can also affect Bihar
Water originating in western Nepal can also reach Bihar through Uttar Pradesh.
The Mahakali River flows towards Uttar Pradesh, where it is known as the Sharda. The Sharda eventually joins the Ghaghara system.
The Karnali River, another major river originating in Nepal, also enters Uttar Pradesh and becomes part of the Ghaghara river system. The Ghaghara subsequently joins the Ganga at Revelganj in Bihar’s Saran district.
In simple terms, major hydrological events in Nepal’s northern and western regions can potentially have downstream implications for Bihar, depending on the volume and speed of water released into connected river systems.
Could another glacier-related event worsen the situation in Bihar?
There is concern because Bihar’s major rivers are already carrying substantial amounts of water.
Following the flooding in Nepal’s Rasuwa district on August 26, all 36 gates of the Gandak Barrage were opened in Bihar to regulate the flow. More than 1.5 lakh cusecs of water per hour was reportedly being released from the Valmikinagar Barrage.
The Central Water Commission has warned of the possibility of large waves in the Gandak and flash flooding in vulnerable areas.
1. Ganga and Gandak systems are already under pressure
According to Bihar’s Water Resources Department, as of the evening of August 27, the Gandak at Dumariaghat in Gopalganj, Ganga in Patna, Budhi Gandak in Khagaria, Ghaghara at Darauli in Siwan and Kosi at Kursela in Katihar had crossed their respective danger levels.
The increase in water flow has already affected low-lying areas. In Khagaria, rising water levels in the Ganga and Budhi Gandak have reportedly inundated 20 panchayats and more than 50,000 houses.
Any additional major inflow from Nepal could put further pressure on these river systems. However, the scale of any impact would depend on the amount of water generated upstream, rainfall conditions and the ability of barrages and river channels to carry the flow.
Chief Minister Samrat Choudhary, after inspecting the situation on August 27, said the danger had not yet passed and urged people to remain cautious.
2. Rainfall could add to the pressure
Another factor is the weather.
Rainfall alerts have been issued for both Nepal and Bihar, with heavy rain forecast in parts of the region. Intermittent rainfall is expected to continue into early September.
If substantial rainfall occurs over the river catchment areas, it could increase water levels in the Gandak, Kosi and other rivers.
For people living along these river systems, the combination of heavy rainfall, high river levels and any sudden upstream water release remains the key concern.
Two factors offer some relief
Despite the risks, there are also reasons to avoid panic.
First, Bihar’s Water Resources Department said that the water levels of Nepal’s 22 monitored rivers were below their danger marks as of the evening of August 27. The Trishuli-Narayani and Bhote Koshi-Sapta Koshi systems were reportedly around four feet and three feet below their respective danger levels.
This indicates that the monitored river levels in Nepal were not uniformly at critical levels at that point. However, conditions can change rapidly during intense rainfall or a sudden glacial or landslide-related event.
Second, the Gandak Barrage still has some water-level margin.
According to the Water Resources Department, the upstream level was 353.770 feet, while the downstream level was 350.930 feet, against a stated benchmark of 362 feet.
The relatively small difference of about 2.84 feet between the upstream and downstream levels indicates that the barrage gates were open and water was being released.
The figures suggest that the barrage was not experiencing the kind of extreme pressure that would, by itself, indicate an immediate structural crisis.
What happens next?
For Bihar, the immediate focus is not simply whether another glacier breaks in Nepal. Authorities will have to monitor rainfall in Nepal, glacial lakes, landslide-dammed water bodies, river levels and the volume of water entering Bihar.
The situation remains fluid.
A second major upstream event could increase the pressure on Bihar’s already swollen rivers, but it would be incorrect to assume that every glacier-related incident in Nepal will automatically result in catastrophic flooding in Bihar.
For now, continued monitoring and timely warnings remain critical for communities along the Gandak, Kosi, Ganga and Ghaghara river systems.
