ISLAMABAD: The water storage capacity of Tarbela Dam has been reduced by 40.58 percent owing to silting in the reservoir as a per the Hydrographic Survey 2017, Adviser to Prime Minister Dr Babar Awan told the Senate on Tuesday.
Responding to a question by Senator Samina Saeed, Awan said as per results of the Hydrographic Survey 2017 of Tarbela reservoir, the live and gross storage capacities of Tarbela reservoir have been reduced by 37.524 percent and 40.58 percent respectively.
He said the best possible arrangements will be made to provide an upstream storage to catch the sediment before entering the Tarbela reservoir.
Inflow of sediment is a natural phenomenon and cannot be prevented. However, the Government of Pakistan has taken steps for construction of Diamer Bhasha Dam which will help reduce the inflow of silt into Tarbela Dam.
Quoting studies, he said, sediment flushing is uneconomical, technically risky and the impact of it on the existing infrastructure will be overwhelming and will impact on barrage operations with increased sediment entering the canals. Additionally, it will accompany the loss of electricity generation at Tarbela and Ghazi Barotha besides the loss of water storage for the irrigation purpose.
Babar Awan said the relevant departments would be directed to arrange a detailed briefing to Upper House of the Parliament on overall situation of dams.
Total sediments deposited in Tarbela reservoir from 1974 to 2017 is 4.731 Million Acre Feet (MAF), Minister for Water Resources Makhdoom Khusro Bakhtiar told Senate Tuesday.
In a written reply to the question of Senator Syed Muhammad Sabir Shah, the minister said the contribution of silt form Siran River is 0.192 MAF which is only about 4.05 percent of the total sediment deposited in Tarbela reservoir so far.
He said it is notable that only 20 percent of Tarbela watershed is under the influence of monsoon.
He said technical investigation of various aspects of the sediment problem at Tarbela have been performed by TAMS Consultants of the project since 1967.
The objectives of this study were to determine possible means of reducing the amount of sediments that would reach the reservoir. The field reconnaissance covered the Indus River up to Parkuta and the lower reaches of Shyok, Shigar, Hunza and Gilgit rivers.
The principal conclusion of the study was that watershed management and upstream debris check dams could accomplish little towards reducing the quantity of the sediments inflow.
He said there is no proposal under consideration of WAPDA to construct check dams on various locations of river Siran to control silting in Tarbela Dam and avail full benefits of the present storage capacity and production of electricity of the dam.