Loss of storage capacity: Senate panel briefed on threats to Tarbela reservoir tunnels

ISLAMABAD: The government Friday said that the loss of gross storage capacity and live storage capacity of Tarbela reservoir is 43 percent and 39 percent, respectively due to sedimentation and any earthquake can choke its tunnels.

Briefing Senate Standing Committee on Water Resources, chaired by Senator Pir Sabir Shah, the officials of Ministry of Water Resources and Wapda deputed at Tarbela reservoir said that the gross storage capacity of reservoir has reduced from 11.62 MAF to 6.53 MAF whereas live storage capacity of reservoir reduced from 9.679 MAF to 5.8 MAF till 2022.

To ascertain the actual sediment inflow in reservoir, annual hydrographic survey of Tarbela reservoir began in 1979 which has been continuously conducted every year. The results of hydrographic survey reveal the average annual sediment inflow in the reservoir to be about 200 million tons (0.100 MAF). It is estimated that useable storage of the project would be reduced to about 1 MAF from 9.67 MAF after a period of 60 to 70 years.

Ministry of Water Resources through Wapda has conducted several sediment management studies as various techniques/methods were recommended by the experts in the studies.

According to Wapda officials the pivot point would be about three miles’ u/s of the dam when the toe of the delta reaches the dam. The potential danger of clogging due to liquefaction of bottom set and fore set slopes would increase as the delta moves closer to the dam.

The Standing Committee was further informed that as a short-term measure, Minimum Operating Level (MOL) of Tarbela has been raised to 1398ft from 1300 ft on the recommendations of experts.

The option of desilting of Tarbela reservoir has been considered and its pros and cons have been evaluated by the sediment experts at length.

After a detailed analysis, the experts have concluded that de-silting of Tarbela reservoir is neither technically feasible nor economically possible.

As a long-term measure, experts have recommended to raise the intake of tunnels to protect the structures from the impact of sedimentation. Accordingly, the Tarbela 4th Extension project was conceived and completed. Similarly, work on raising of T-5 intake is under way.

The officials further stated that with construction of Diamer Bhasha reservoir, the volume of silting in Tarbela will reduce.

During discussion, hot debate was witnessed between Senator Dr Muhammad Hummayun Mohmand and PPP Senators Qurat-ul-Ain Marri and Senator Taj Haider, when the former asked questions about the key reasons of not evolving a consensus on mega reservoirs.

Chairman Pakistan Council of Research in Water Resources (PCRWR) informed the committee that Pakistan is heading towards becoming a water scarce country by 2025 as Pakistan has not built reservoirs, adding that Pakistan has lost $ 90 billion worth of water due to recurring floods since 2010. He said, water table in Quetta, Islamabad and other cities is going down, proposing change in water usage habits.

Copyright Business Recorder, 2022