The 1.4km tunnel will carry water from the reservoir to the two-turbine underground power station.

The first of the three construction packages (headworks, waterways, power plant, hydromechanical works, and the 33km transmission line) began in December 2018. The project is due to be commissioned in 2026.

The Tanahu hydropower project, located on the Seti River, about 150km west of Kathmandu, is estimated to generate around 1.1 terawatt hours (TWh) of energy, with an initial output of 586 gigawatt hours (GWh) expected within the first decade.

Contractor Tractebel, in collaboration with Canada’s Manitoba Hydro International, is responsible for the preparation of tender documents, tender evaluation, construction supervision, design checking, and advisory services during project operation and maintenance.

Tractebel senior engineering geologist Renos Christakis said because the headrace tunnel was the only waterway between the reservoir and the underground powerhouse, resilience and serviceability were vital for the lifetime of the project.

“For the last 29 months, the contractor’s designer, its engineering geologists and hundreds of workers, with the support and technical input of Tractebel and in particular its geologists, worked together and managed to excavate a large-span underground structure through challenging rock mass conditions; conditions that required excellent co-operation, mutual understanding, real-time support optimisation techniques, diligent monitoring and above all, engineering integrity,” he said.