Kathmandu — The devastating Bhote Koshi floods have prompted calls to revise hydropower project design standards in Nepal after extensive damage to surface structures and underground powerhouses exposed serious gaps in worker safety and emergency evacuation arrangements.
The floods damaged both operational and under-construction hydropower projects, with water entering underground powerhouses through main access tunnels and trapping workers. The disaster raised concerns about how employees can be rescued during extreme floods and where they can take shelter or escape when underground facilities become inaccessible.
According to the details reported, six people were trapped in the underground powerhouse of a 22-megawatt hydropower project. The bodies of five were recovered, while one person remained missing. At the 111-megawatt Rasuwagadhi Hydropower Project, 93 people were present, and the bodies of seven were recovered. At the Upper Trishuli-3A Hydropower Project, two people were rescued alive, while 39 remained unaccounted for.
Two people trapped at the Nepal Electricity Authority (NEA)-built Upper Trishuli-3A project were rescued 10 days after the flooding. Similarly, Chinese nationals trapped in a tunnel at the 216-megawatt Upper Trishuli-1 Hydropower Project, being developed under the leadership of Korean companies, were rescued unharmed 11 days after the disaster.
Overall, around 800 people were reported missing or unaccounted for from operational and under-construction hydropower projects affected by the Bhote Koshi floods.
Floodwaters swept away surface structures so extensively that virtually no trace of some facilities remained. At Upper Trishuli-3A, locating the project site, workers’ camps and tunnels became extremely difficult after floodwaters submerged the area. The disaster raised urgent questions about how workers trapped in underground powerhouses could be rescued and how they could reach safety during similar events.
Experts said the floods exceeded the levels anticipated in conventional design assessments. Although underground structures are generally considered safer against earthquakes, floods and landslides, the Bhote Koshi disaster demonstrated that they are not necessarily safe when floodwater enters through tunnels connecting them to the river.
Experts call for emergency escape tunnels
Civil engineer and energy expert Taranath Sapkota said underground powerhouses should have tunnels connecting them to safe locations, while surface powerhouses should also include emergency escape routes. He said the damage to operational and under-construction projects showed that greater attention must be given to project design.
Sapkota said hydropower projects are generally designed using flood data covering a maximum period of 100 years, but the Bhote Koshi disaster showed that such assessments might no longer be sufficient.
He stressed that developers should analyse the entire river basin when planning hydropower projects, particularly in areas where multiple projects share the same river system. He also called for revised design criteria and greater attention to worker safety.
The orientation of access tunnels was another important factor. Except for Upper Trishuli-1, the river-facing structures of the affected projects were aligned with the direction of river flow. Experts said this allowed floodwater to enter through the inlets of the main tunnels and reach underground powerhouses.
At Upper Trishuli-1, the access tunnel leading to the powerhouse was oriented away from the direction of river flow, preventing floodwater from entering through the tunnel entrance. Workers there remained safe. Experts have suggested adopting similar design approaches, installing automatic gates and constructing separate escape tunnels for underground facilities.
Existing escape arrangements proved insufficient
Former president of the Nepal Tunnel Association Gyanendra Lal Shrestha said escape tunnels are generally designed to allow workers to exit during emergencies such as fires or short circuits. However, these tunnels usually connect to the main tunnel rather than providing an independent route to the outside.
Underground powerhouses also have ventilation tunnels containing enough oxygen for several days, but separate escape routes leading to higher ground had not previously received sufficient attention.
Shrestha said underground powerhouses are generally built when surface space is limited or other circumstances make them necessary, and they are more expensive to construct. However, he said safety considerations must now take priority alongside construction costs.
He added that developers of projects under construction should be consulted about building separate escape tunnels leading to higher ground. Experts have also recommended providing dedicated emergency shelters where workers can remain safe until rescue teams reach them.
Glacial lake risks extend beyond Bhote Koshi
The risks are not limited to the Bhote Koshi River. The headwaters of other major rivers in Nepal also contain glacial lakes, raising concerns that similarly devastating disasters could occur if these lakes burst.
According to the United Nations Development Programme’s Inventory of Glacial Lakes 2020, there are 3,624 glacial lakes across Nepal’s Koshi, Gandaki and Karnali river basins, as well as in China and India. Of these, 2,060 are in the Koshi Basin, 1,128 in the Karnali Basin and 432 in the Gandaki Basin.
The Koshi Basin comprises the Tamor, Arun, Dudhkoshi, Likhu, Tamakoshi, Sunkoshi and Indrawati sub-basins. The Gandaki Basin includes the Trishuli, Budhi Gandaki, Marshyangdi, Seti and Kali Gandaki sub-basins. The Karnali Basin comprises the Bheri, Tila, Mugu, Kuwari, West Seti, Humla, Kali and Karnali sub-basins.
Hydropower projects have already been built or are under construction across these sub-basins, increasing the importance of assessing risks across entire river systems rather than considering individual projects in isolation.
Calls for updated scientific and technical standards
Subarnadas Shrestha, former president of the Independent Power Producers’ Association, Nepal (IPPAN), said floods and landslides have caused significant damage to Nepal’s hydropower sector every year since the 2015 earthquake. He cited damage in the Mai Khola area of Ilam, the Bagmati and Heuwa corridors, and the recent disaster in the Bhote Koshi.
He said the Bhote Koshi incident demonstrated that underground construction alone could not guarantee safety.
“We built underground structures, but we failed to adequately address how to protect the lives of the people working inside them,” he said, stressing the need to prioritise human safety alongside underground technology.
Bikash Adhikari, head of the Department of Environmental Engineering at Kathmandu University, said hydropower design standards must be revised immediately. He said structures designed using historical data and 100-year flood estimates had suffered extensive damage from debris-laden floods.
Adhikari said conventional river-flow models had become inadequate due to accelerated glacier melting, the risk of glacial lake outburst floods and changes in river sources. He added that Nepal continues to rely on standards developed decades ago or adopted directly from India, China and European countries, which may not adequately account for local climatic conditions.
He called for Nepal-specific scientific standards, satellite technology and artificial intelligence-based systems. He also recommended installing automatic gates at water intakes and tunnels so that tunnel entrances could be closed when floodwaters approach.
Government forms committee to review designs
Energy Ministry spokesperson and Joint Secretary Mohan Kumar Shakya said a scientific and technical committee had been formed under the Water and Energy Commission Secretariat to study hydropower project designs and the possibility of similar disasters in other river corridors.
The committee will recommend the changes needed in hydropower project designs and propose appropriate technical standards. The ministry will make decisions based on its findings, Shakya said.
Billions invested in hydropower projects
According to IPPAN, 347 operational and under-construction hydropower projects with a combined capacity of 7,251 megawatts have attracted investments of Rs 1.243 trillion.
Another 576 projects with a combined capacity of 27,535 megawatts are at various stages of development, including surveys, studies, design and applications for survey and construction licences. Investments in these projects total Rs 6.662 trillion.
The Bhote Koshi disaster has intensified calls for Nepal to update hydropower design standards, strengthen flood-risk assessments and ensure that emergency escape routes, safe shelters and rescue provisions are incorporated into project designs. Experts say the growing scale of hydropower development makes it increasingly important to protect both infrastructure and the people working within it.
Kantipur