WAPDA executing Tarbela 4th extension hydropower project
18 June, 2016
LAHORE: The Pakistan Water and Power Development Authority (WAPDA) is executing Tarbela 4th extension hydropower project (T4) to generate 1,410MW electricity with its scheduled completion in February 2018.
However, an accelerated construction programme was devised with approval of the World Bank – the 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 – 1,512 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 would be continued until the reservoir level reaches 1,483 feet.
It was considered that the water level in the reservoir would raise to 1,483 by mid July 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 1,505 feet. 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 May and June, respectively. Maximum capacity to release water from tunnel 1, 2, 3 and 5 is 190,000 cusecs, whereas current inflow is more than 250,000 cusecs. Consequent to the high water inflows, the reservoir will attain the level of 1,483 feet by June 19. 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 ongoing works on T4 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 the IRSA indent.
The IRSA wrote a letter to the project authorities that in view of existing trend of inflows in the Indus River, it is expected that Tarbela may touch to 1,490 SPD level by June 30, despite the maximum release from the dam. This eventuality is likely to adversely affect the ongoing work on Tarbela 4th extension hydropower project.