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Nepal is promoting hydropower as a foundation for its economic development. Theoretically, about 83,000 MW of electricity can be generated, while only around 5 percent of this potential has been developed so far. The government is focusing on the hydropower sector because Nepal’s favorable topography, high-gradient rivers and significant hydropower potential are expected to strengthen national energy security, support industrialization and expand electricity exports. Hydropower is essential to the economy and to meeting the country’s growing energy demand. The government also aims to completely replace fossil fuels by 2045, with hydropower serving as the backbone of this transition.

The Electricity Development Department has already issued construction licenses for around 263 projects with a combined capacity of 13,177.42 MW, while the number of survey licenses continues to increase. Hydropower development is advancing rapidly, with numerous companies involved in the sector. However, amid the race to increase installed generation capacity, an important question requires attention: Are worker safety and emergency preparedness receiving the attention they deserve?

Most hydropower projects constructed in Nepal’s mountainous terrain include long headrace tunnels. These tunnels convey water from the dam site to the powerhouse and form a critical component of a project’s hydraulic system. Tunnels and underground powerhouses are essential components of hydropower projects and must be designed with great care.

Floodwater intrusion, landslides, debris flows blocking tunnel portals, tunnel inundation, structural damage or ventilation-system failures can rapidly isolate workers from the outside world. One of the most serious vulnerabilities in such situations is dependence on a single access route. If the main tunnel portal is blocked by flooding, landslides, rocks, debris or structural damage, rescue teams may have no way to reach people trapped inside. In such circumstances, removing the obstruction from outside or attempting to create a new access route may be the only option, significantly delaying rescue operations.

Therefore, a fundamental question must be addressed during the design of hydropower tunnels: If the main entrance is completely blocked, how will rescuers reach the people inside?

Depending on project size, tunnel length, geological conditions and the level of identified risk, the feasibility of an emergency escape route, rescue adit, alternative access tunnel or cross-passage should be assessed during the design stage. Construction, test and access tunnels can also be designed from a safety perspective so that they can be used during emergencies. In suitable geological and topographical conditions, a vertical emergency shaft connecting the tunnel to the surface may provide an alternative means of access or evacuation. If the main tunnel becomes inaccessible, such structures could provide workers with an exit and rescue teams with an alternative entry route.

However, an alternative exit alone is not sufficient. Another critical life-safety requirement is a reliable ventilation system. During an emergency, the main electrical supply may fail, shutting down ventilation equipment. Inside a tunnel, deteriorating air quality, reduced oxygen levels, dust, smoke, harmful gases and rising temperatures can create life-threatening conditions.

Therefore, an independent emergency ventilation system, supported by backup power, emergency lighting and reliable communication systems, should be considered an essential component of tunnel safety planning. For tunnels where immediate evacuation may not be possible, the feasibility of refuge chambers or protected emergency shelters should also be evaluated. Such facilities can provide protection and may be equipped with breathable air, communication facilities, emergency power and other essential life-support systems.

The devastating flood in the Trishuli region and the difficulties experienced in rescuing people trapped inside a tunnel should not be regarded merely as another disaster. The incident raises serious questions about Nepal’s approach to hydropower and tunnel design.

Engineers calculate flood discharges, determine tunnel hydraulic capacity, design support systems and assess rock-mass conditions. However, an equally important question must be asked: If a tunnel is completely blocked and people are trapped inside, what alternative rescue system is available?

Future hydropower projects in Nepal must move away from a single-point-of-failure approach. A situation in which the failure of one portal, one access route or one ventilation system causes the entire emergency response system to fail should not be acceptable. Risk-based design must incorporate a level of redundancy and independent backup systems.

The challenges faced during rescue efforts in the Trishuli region show how difficult such operations can be when alternative access routes are unavailable. If proper emergency access and backup systems had been in place, the rescue could potentially have been carried out more quickly and effectively, reducing the risks faced by those trapped inside the tunnel.

The Government of Nepal should therefore consider requiring an Emergency Access and Evacuation Plan before approving projects involving tunnels. Based on tunnel length, geological conditions, topography and risk assessments, projects should be required to evaluate the need for emergency exits, rescue adits, emergency access shafts or refuge chambers. Independent backup ventilation, emergency power supplies, communication systems, hazardous-gas monitoring and regular emergency rescue drills should also be incorporated into project design.

The Trishuli disaster has delivered an important lesson: a hydropower tunnel is not merely a structure for conveying water; the safety and survival of the people working inside it must also be central to its design.

Future hydropower development cannot focus solely on increasing megawatt capacity, reducing costs and accelerating construction. Extreme rainfall, exceptional floods, debris flows, landslides and the increasing risks associated with climate change and global warming must be incorporated into hydropower tunnel design and safety assessments.

The guiding principle for Nepal’s hydropower development should be clear: If people are trapped inside a tunnel, there must be a safe and practical means of reaching or evacuating them, even if the main entrance becomes inaccessible. A tunnel constructed for power generation must never become a death trap during an emergency.

The Trishuli disaster should not be remembered only as an accident. It should be treated as a lesson and a turning point for improving the safety standards and emergency design of Nepal’s future hydropower tunnels. While catastrophic events may be impossible to prevent entirely, their devastating impacts can be reduced through sound geological understanding, rigorous risk assessment and appropriate engineering design.

The author is a geologist and Master of Geoscience graduate specializing in Mining and Mineral Exploitation. His interests include engineering geology, mineral resource exploration and exploitation, mine design and infrastructure development in Nepal. He currently works as an Exploration Geologist with a consultancy company.