More Renewable Energy for Nepal: River Diversion at Tanahu Project

Surrounded by the spectacular panorama of the Himalayan mountains, the Tanahu hydropower project (HPP) reached a major milestone in November 2023: diversion of the Seti River around the dam site. Located about 150 km west of Kathmandu, this storage-type hydropower project has a planned installed capacity of 140 MW and an estimated energy generation of 585.7 GWh within the first ten years. At 140 m high, the concrete gravity dam, with a storage reservoir of a total volume of some 295 million m³, will be the largest dam in the country. Our hydro experts are an integral part of this monumental initiative.

River diversion ceremony on November 6, 2023

Tractebel supports tendering, construction supervision and design checks.
Our team from Tractebel in Germany, in association with Canadian-based Manitoba Hydro International, has been awarded the contract by client Tanahu Hydropower Limited for:

• Preparation of tender documents
• Tender evaluation
• Construction supervision
• Design checking
• Advisory services during project operation and maintenance

Construction began in 2018 and the project is expected to be commissioned in 2026.

Dam abutment excavation, October 2022

Securing Nepal’s seasonal energy supply
For now, the Seti River, on its way from the Annapurna Massif to the Bay of Bengal, is diverted around the dam foundation pit. Once the dam is completed as scheduled in 2026, the diversion tunnels will be permanently plugged. The dam will form a massive reservoir to buffer the fluctuating river flow, which varies from tens of m3/sec during the dry season to some thousand m3/sec during the July to October monsoon. The Tanahu project, designed for peak operation during the driest months of the year, will generate renewable electrical energy year-round for several hours per day. The HPP will play a vital role in Nepal’s seasonal energy security and reduce dependence on imported energy.

The diversion tunnel under construction in April 2023

And then in June

140 MW to hit the grid by 2026
The dam will sit in a narrow canyon close to the end of a steep valley formed by the Seti River, and takes advantage of ideal natural boundary conditions. Fed through a 1.4-km headrace tunnel, the two Francis turbines in an underground powerhouse with a total capacity of 140 MW will generate an estimated over one TWh, including 586 GWh within the first 10 years. Additionally, the separate facilities for environmental flow will generate around 1.8 MW of power.

   
The underground powerhouse, March 2023

Tanahu dam site, October 30, 2023

‘With a large gravity dam, several kilometers of tunnel systems, and an underground power plant of considerable size, the Tanahu project is of national importance. It is characterized by its multidisciplinary nature, considering the large number of international actors involved. The river diversion is an important milestone in the Tanahu hydropower project, for Tractebel and partners and for Nepal, one of our most important markets for hydropower development. The Nepalese people and economy will greatly benefit from the renewable, sustained energy provided Tanahu. The project will further stabilize the national grid, while supporting the economy with the returns of exporting energy to neighboring countries such as India.’


Dr. Frank Zöllner, Acting Project Manager, Tractebel in Germany