LAHORE: Pakistan Water and Power Development Authority (WAPDA) is executing Tarbela 4th Extension Hydropower Project (T4) to generate 1410-MW electricity with its scheduled completion in February 2018. However, an accelerated construction programme was devised with approval of World Bank - financer of the project - to complete the project by mid 2017 to benefit from the high water flow season of the year.
To execute T4 project, intake structure of Tunnel No. 4 was redesigned to fit generating machines. With a view to carrying out construction work to modify the intake tunnel in accordance with its new design, a concrete coffer dam was built in the reservoir. Height of the coffer dam i.e. 1512 feet above mean sea level was ascertained in consultation with Indus River System Authority (IRSA) and keeping in view the water inflow pattern to the reservoir, where construction work can be continued until the reservoir level is reached 1483 feet. It was considered that the water level in the reservoir would rise to 1483 by mid July 2016 and subsequently over flow the coffer dam. It is pertinent to mention that water from Tarbela can be released through spillways once the reservoir attains the level of 1505 feet. Prior to this level, water flows out of the reservoir from tunnel No. 1, 2, 3 and 5.
Due to pre-monsoon rains and abnormal increase in temperature in the catchment areas, Indus River average inflows are 27,000 cusecs and 53,000 cusecs higher than the last five years average during the May and June respectively. Maximum capacity to release water from tunnel 1, 2, 3 & 5 is 1,90,000 cusecs, whereas current inflows are in the range of more than 2,50,000 cusecs. Consequent to the 99ohigh water inflows, the reservoir will attain the level of 1483 feet by June 19, 2016. Resultantly, the work on intake of tunnel 4 will have to be stopped due to overlapping of coffer dam. This eventuality is likely to adversely affect the on-going works on T-4 project, as completion of construction work on the intake of tunnel 4, which was planned to be completed by mid July 2016. It is pertinent to mention that construction work on intake tunnel of Tarbela 4th Extension Hydropower Project was also suffered last year for about 4-6 weeks due to erratic flows and early increase in reservoir level and its late depletion in accordance with IRSA indent.
IRSA wrote a letter to the project authorities that in view of existing trend of inflows in the river Indus it is expected that Tarbela may touch to 1490 SPD level by June 30, 2016 despite the maximum release from the dam. This eventuality is likely to adversely affect the ongoing works in Tarbela 4th Extension Hydropower Project.
A high level technical team headed by Member (Water) will immediately leave for Tarbela Dam to coordinate with the contractor for expediting the construction work on intake of tunnel 4 to the maximum in the remaining days till water attains the level of 1483 feet.
World Bank - financer of the project - will be immediately informed of the phenomena, as accelerated construction work was also approved and is being monitored by the bank.
Contractor to be pursued for carrying out the work round-the-clock to attain maximum progress in the intake area before overlapping the coffer dam.