New Delhi: Ahead of its commissioning slated for October this year, Prime Minister of Bhutan Tshering Tobgay has inaugurated the initial reservoir filling of the India-funded 1,020 MW Punatsangchhu-II hydroelectric project in Bhutan in the presence of Indian Ambassador to the Himalayan kingdom Sudhakar Dalela.
Among others present during the event held on Wednesday were Bhutan’s Minister for Energy and Natural Resources Gem Tshering and the chairman of the Punatsangchhu Hydroelectric Project Authority (PHPA) Tandin Wangchuk, the PSU Connect news website reported.
Reservoir filling is an important activity in the concluding phase of constructing a hydroelectric power plant. This process typically involves finalising the river diversion scheme closure, initiating the functionality of discharge structures, and commencing powerhouse operations. Successful completion of this task marks the readiness to initiate power generation within the hydroelectric power plant.
The Punatsangchhu II is a run-of-the-river hydroelectric power generating facility in the Wangdue Phodrang district of Bhutan. The project is being developed by the Punatsangchhu II Hydroelectric Project Authority (PHPA II) under an inter-government agreement between the Government of India and the Royal Government of Bhutan.
According to the PHPA-II website, the project was sanctioned at a cost of Rs 37,778 million (base cost excluding interest during construction and March 2009 price level) with an installed capacity of 990 MW (latter on revised to 1,020 MW). It is completely funded by the Government of India - 30 percent in the form of a grant and 70 percent as a loan component at 10 percent annual interest.
India’s Water and Power Consultancy Services (WAPCOS) provided engineering and design consultancy services during the project study phase, while the National Institute of Rock Mechanics (NIRM) was engaged for modelling and geotechnical engineering services.
Construction of the project started in December 2010 with an ambitious completion schedule of seven years, including two years of infrastructure development. However, that deadline could not be met and a second deadline of end of 2022 was set. However, the second deadline too was missed and the final deadline for commissioning of the project has now been set for October 2024.
The project is located on the right bank of Punatsangchhu river along the Wangdue-Tsirang highway between 20 km and 35 km downstream of Wangdue Bridge. The dam site is about 94 km from Thimphu along the highway. Paro, the nearest airport is about 125 km away. The nearest railway station is at Hasimara on Siliguri-Alipurduar Broad Gauge line of India’s Northeast Frontier Railway. The project area is also accessible from Bagdogra Airport near Siliguri in West Bengal and via Phuentsholing-Semtokha (near Thimphu)–Dochula (about 440 km). The project area can also be approached from the proposed Gelephu smart city near the south central border of Bhutan.
The Punatsangchhu river originates at the confluence of the rivers Phochhu and Mochhu at an altitude of about 1,200 metres above sea level at Punakha. The Punatsangchhu river then flows southerly to enter the Indian plains of West Bengal and eventually flows into the Brahmaputra.
The diversion dam of the run-of-the-river Punatsangchhu-II hydroelectric project is located about 20 km downstream of Wangduephodrang bridge. All other project components are situated on the right bank. Its underground power house is 15 km downstream of the dam at Kamechu, Dagar Gewog (administrative unit under a district in Bhutan).
The Punatsangchhu II hydroelectric project encompasses the construction of a concrete gravity dam measuring 91 m in height and 223.8 m in length. Additionally, it includes the establishment of an 877.46 m-long diversion tunnel with a diameter of 12 m, capable of discharging 1118 cubic metres of water per second.
The project also incorporates the construction of an upper cofferdam, measuring 168.75 m in length and 22 m in height, as well as a downstream cofferdam with dimensions of 102.02 m in length and 13.5 m in height. The primary dam will be equipped with seven sluice gates, each measuring 8 m in width and 13.20 m in height.
The power plant will have an underground powerhouse measuring 240.7 m in length, 23 m in width and 51 m in height. It will have six units of 170 MW each.
According to Ramesh Kumar Chandel, managing director of PHPA-II, of these six units, two will be ready for commissioning by October 2024. The rest four will be commissioned by the end of this year, Chandel told Bhutan’s Kuensel newspaper in August last year.
Once fully commissioned, the Punatsangchhu II hydroelectric project will generate 4,357 million units of electricity annually. All the surplus power generated from the project will be exported to India.
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