AFTER SUFFERING SEVERE flood damage in August 2000, Bhutan’s ambitious 1020MW Tala project is back on track for completion in March 2005, only three months behind the original schedule, according to Tala Hydroelectric Project Authority (THPA) chairman Lyonpo Khandu Wangchuk.

Immediately after the damage, likely completion was feared to be as late as March 2006, 15 months after its original 15 December 2004 target. If the new date can be met, some of the slippage that occurred before the floods will also have been recovered.

Tala is an impoundment/run-of-river project on the Wangchu tributary of the Brahmaputra river in western Bhutan, whose 92m high dam will store sufficient water to feed a 23km, 50m2 headrace tunnel year-round.

All the main elements except the dam and switchyard are underground.

Power will be evacuated via 400kV double circuit transmission lines to the Bhutan-India border 63km from the power house, after which it will be carried a further 1500km inside India to the New Delhi area. Construction under five civil works contracts began in November 1998 after THPA had already completed some 80km of access roads to five sites on the river. Hindustan Construction Company (HCC) and Jaiprakash Industries have two contracts each while Larsen & Toubro (LT) has the final and smallest contract.

LT also has the transmission line contract to the Bhutan-India border on which work has also already begun. Indian government-owned Bharat Heavy Electricals (BHEL) is undertaking the electro-mechanical work while Power Grid India is responsible for the Indian portion of the transmission line. Virtually all power will be exported to India.

Rapid mobilisation on site was assisted by THPA who supplied a starter pack of basic equipment for each contract on a cost reimbursement basis. However, extremely difficult geological and weather conditions soon caused difficulties.

For example, Jaiprakash Industries quickly faced a 15m long face collapse on C-2 when its tunnel intersected an aquifer. More recently, HCC has also reported tunnelling difficulties.

The major challenge so far, however, occurred when 1700mm of rain fell from 1-3 August 2000. Eight of the 1000 plus workers at the five sites were either buried in landslides or washed away. Indian Air Force helicopters had to drop food and medicines to over 800 others who were marooned. Roads were cut, bridges, protection works and site camps washed away, and on site power transmission and telecom lines lost.

Total costs, including contractors’ compensation, came to US$19M out of a total project budget of US$720M. It was feared the event would delay the project by nine months in addition to the six-month slippage that had already occurred.

But recovery has been largely completed. An accelerated construction schedule, as well as rapid reimbursement of contractors’ claims, has meant that some 40% of the project was completed by late 2001. This is only marginally behind the original schedule and includes 17km of headrace tunnel.