Indian companies have won all five contracts for the civil works at Bhutan’s 1020MW Tala hydro project. In October Hindustan Construction of Mumbai and Jaiprakash Industries of New Delhi were awarded the most lucrative contracts, worth a total of US$209M, by Tala Hydro- electric Project Authority, the developer.

The project’s civil works were divided into five packages: the dam, intake and desilting system, and the first 6km of the 22.64km-long headrace tunnel (C1); 5.2km of the headrace tunnel (C2); 4.4km of the tunnel (C3); 7.1km of the tunnel (C4); and the construction of the powerhouse complex (C5).

Hindustan Construction was awarded both the dam complex package (C1), worth US$77.7M, and C4, valued at US$31.3M. Jaiprakash Industries was awarded construction of the powerhouse complex (C5), worth US$77.3M, and the second part of the headrace tunnel (C2), valued at US$22.8M. These contracts are scheduled for completion in 66 months. Larsen and Toubro of Chennai received the C3 package, a contract worth US$21.2M, also for completion in 66 months. Supply and erection of electrical generating equipment has been entrusted to another Indian company, Bharat Heavy Electricals.

The Tala project dates back to 1995, when Bhutan and India agreed jointly to develop the US$400M scheme sited in the Wangchu river basin, southern Bhutan. Construction took off with a groundbreaking ceremony in April 1997. Work on access roads, site infrastructure and power lines is now at an advanced stage.

The project is being executed by the Tala Hydroelectric Project Authority (THPA) which is an autonomous body set up by the Royal Govern-ment of Bhutan and the Government of India. Water and Power Consultancy Ser-vices of India (WAPCOS) is the consultant for the project. WAPCOS is being assisted by other Indian Government bodies, including the Central Water Commission, Central Electric-ity Authority, Geological Survey of India, Survey of India and the Central Water and Power Research Station.

The project is fully funded by the Government of India, with a grant of 60% of the cost and a loan of 40%. It is scheduled for completion in 2004. Once completed, India will operate the project for two years, then transfer control to the Government of Bhutan. India will purchase its surplus power.

This is the second India-Bhutan bi-national hydro power development, following the construction of the 336MW Chukha scheme which was completed in 1986. Bhutan has immense hydroelectric potential, estimated at approximately 12,000MW. To date Chukha is its only large hydro power plant, but more are in the pipeline: the 45MW Kurichi hydro power project, designed and constructed by NHPC of India; and the Austrian-funded 23.8MW Basochhu project, scheduled for commercial operation by the end of 1999.

Bhutan’s electricity supplies are due to be extended to rural areas in pace with the construction of the new power stations. As regards the rest of the power, within 10-12 years export of electricity to India will become Bhutan’s most important source of national revenue. As a result, Bhutan’s economic situation will depend on whether it gets a reasonable price for the electricity it supplies; recently proceeds from Chukha have been significantly below world market prices.

The Tala project

Tala comprises a 92m-high concrete gravity diversion dam, with a crest length of 130m and a crest elevation of 1343m. It will impound a reservoir with a capacity of 9.8 x 106m3. It will also include three underground desilting chambers; a flushing tunnel for sediment; a 22.7km-long concrete-lined headrace tunnel; an underground powerhouse housing six five-jet 170MW Pelton turbines; and transmission lines connecting to the Indian and Bhutan electricity grids.
The concrete dam, which will be constructed 3km downstream of the tailrace tunnel exit of the 336MW Chukha plant, will divert water into three desilting chambers and transfer it further on into a modified horseshoe headrace tunnel.
From there it will be transferred up through a 178m-high underground surge shaft near the village Tala, and then down through two 1.1km-long, 4m-wide steel-lined pressure shafts towards the underground powerhouse. Each pressure shaft will divide into three branches, putting into motion the six turbines.
The project has a high gross head of 860m for power generation. It will operate with a design discharge of 142.5m3/sec to provide an average annual generation of 4865GWh.