ISLAMABAD - The water storage capacity of Tarbela Dam has been reduced by 40.58 percent owing to silting in the reservoir as a per Hydrographic Survey 2017, Adviser to Prime Minister Dr Babar Awan told Senate on Tuesday.

Answering a question of Senator Samina Saeed, he said as per results of Hydrographic Survey 2017 of Tarbela reservoir, since operation 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 arrangement will be to provide an upstream storage to catch the sediment before entering the Tarbela reservoir. There is no provision for raising of Tarbela Dam.

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. Wapda had conducted sedimentation studies in the years 1987, 1991, 1997, 1998, 1999, 2007, 2013 and 2014 for evaluation of possibilities of desilting Tarbela reservoir.

Quoting studies, he said, sediment flushing is uneconomical, technically risky, impacts on the existing infrastructure will be overwhelming resulting into increased variation in bed profile of downstream river system 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. Hence the desilting is neither technically feasible nor economically favourable.

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.

4.731MAF SEDIMENT DEPOSITED IN TARBELA

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. Seran catchment forms hardly two percent. The investment made for reducing sediment yield in this small catchment area does not make it a viable project like at Mangla where almost all catchment area is favourable for watershed checks and interventions.

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.

INP adds: The government is continuously trying to engage government of Afghanistan into dialogue for a possible water treaty in future or at least to develop mechanism for sharing of information between the countries.

In response to a question of Senator Dr Jehanzeb Jamaldini in the Senate, in a written response on Tuesday, the government said the sharing of information between the two countries will include knowledge about the future impacts on the flows from Afghanistan but so far Afghanistan is non-responsive to the Pakistani initiative.

The government of Afghanistan has reconstructed the hydropower projects destroyed during the war including Kama and some other hydroelectric plants, therefore, till to date there is no impact on the inflows in the common rivers with Afghanistan. However, there are certain new projects in the pipeline as per information gathered from different sources. After the completion of the new projects there will certainly be some impact on the water inflows in the common rivers.

An Afghanistan Cell has been established in the office of Pakistan Commissioner for Indus Water which collects data through different sources and is monitoring inflows on the common rivers with Afghanistan.