Mangdechhu hydroelectric project - A game changer for Bhutan
The Mangdechhu hydroelectric plant in central Bhutan, the country’s latest hydro plant to come online, has brought a significant increase in the installed power capacity, providing additional energy security nationally as well as the opportunity for further exports to India.
The Mangdechhu hydroelectric plant on the Mangdechhu River in the Trongsa district of central Bhutan is considered a gamechanger for the mountainous landlocked Himalayan country.
The 720MW run-of-river project, which was inaugurated after threemonth commissioning in August 2019, is the country’s second-largest power project to date and marked an almost 50% increase in the installed hydro capacity.
On 2,335MW currently, hydro accounts for 99% of the power generation capacity, with the majority of the rest diesel-powered generation.
The project was conceived in 2010 in a bilateral agreement with the government of India, to which Bhutan is an important exporter of energy – particularly in the wet summer months when the generation output far exceeds the local requirements.
With financial support from the Indian government in the form of a combined grant and loan, the project was completed within seven years from the award of the major civil, electromechanical and hydromechanical packages in March 2012.
The concrete dam, the work of Indian conglomerate Jaiprakash Associates Limited, has a height of 56m above the river bed level and is 141.28m long and with a top width of 10m.
The plant is comprised of a 682m, 8.5m diameter diversion tunnel, 13.56km, 6.5m headrace tunnel and 1.33km, 8m diameter tailrace tunnel.
Other constructions included two 340m long desilting chambers, a 13.5m, 152m deep surge shaft, two 1.86km, 3.5m diameter steel-lined pressure shafts, a 155m, 41m deep underground powerhouse cavern and a 135m, 23m deep underground transformer cavern.
Other key contractors were Gammon India Limited/Gammon Engineers & Contractors, PES Engineers and Kalpataru India from India, Alstom/GE T&D, and Hyosung Corporation and L S Cable from South Korea.
The four hydro turbines are Pelton wheel turbines, each rated for a head of 692m and 180MW capacity.
The design output is 2,925MWh based on 95% machine availability. Power evacuation is via a 400kV double line transmission corridor via Jigmeling in southern Bhutan to Alipurdwar in West Bengal.
In addition to the short project execution timeframe, another key standout is its cost, which is estimated to total around Rs.5110 crores ($700.69 million). This corresponds to a cost per megawatt of around Rs.7.1 crores ($0.97 million).
“The Mangdechhu plant is an exemplary project,” says AK Mishra, Managing Director of the Mangdechhu Hydroelectric Project Authority, which was founded to manage its development.
“This is the most economical project for cost and time when compared with the contemporary hydropower projects of similar size and capacity in the South Asian cooperation region.”
The project was recognized for “outstanding civil engineering works” with the award of the Brunel Medal – named after the 19th-century engineering giant Isambard Kingdom Brunel – from the UK Institution of Civil Engineers in October 2020.
Among other notable features was the creation of 500 new jobs for engineers and support staff locally, benefitting affected families among others.
The project has also supported various schools and health facilities with the upgrading of infrastructure and has provided drinking water and water irrigation facilities.
Mishra comments that various challenges were encountered, notably around the technical complexities of the project with placements, and non-shifting of underground structures in a low dipping shear zone, as well as on contractual issues and coordination and implementation.
“These involved out of the box thinking from the project management side and we introduced new technologies and construction methods to expedite the excavation and concreting works.”
The Mangdechhu project is registered as a clean development mechanism project with the UN Framework Convention on Climate Change (UNFCCC) and is estimated to achieve savings of 2.4Mt CO2e annually.
The initiative also intends to earn revenue from carbon trading.
FUTURE HYDRO PROJECTS
Mangdechhu is the first to be completed of the ten hydro megaprojects totalling 10,000MW in various stages of development in Bhutan with support from the government of India.
The next most advanced are the Punatsangchhu I and II projects of 1,200MW and 1,020MW capacity respectively in the Wangdue Phodrang district in western Bhutan. Of these, Punatsangchhu II is due to come into operation in 2022 followed by Punatsangchhu I in 2025.
Others include the 600MW Kholongchhu, 180MW Bunakha, 570MW Wangchu and 770MW
Chamkarchu schemes, which are to be constructed under a joint venture model. Of these, the most advanced is Kholongchhu in Trashiyangtse district of eastern Bhutan, for which the foundation stone was laid by Indian Prime Minister Narendra Modi in 2014 and the concession agreement signed in June 2020. The operation may start in late 2025.
Looking ahead, Mishra says that some key learnings that emerged from the Mangdechhu development that can be applied to future projects include the importance of the adoption of a standard bidding document by the development authority and the need for efficient monitoring of every aspect of the development.
“We carefully monitored the overall progress on daily, weekly and monthly timeframes and with the limited manpower we also monitored the productivity to meet the time and cost targets,” Mishra says.
Another is the settlement of contractual issues and claims in parallel with the execution of the works.
India and Bhutan have a long history of hydropower relations, dating as far back as 1961 with the Jaldhaka project, which was built at the joint border with the powerhouse on the Indian side but initially most of the power production was exported to southern Bhutan.
These relations form the centrepiece of the countries’ economic cooperation and are mutually beneficial in terms of providing clean electricity to India, generating export revenue for Bhutan and further strengthening the bilateral economic linkages.
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