ISLAMABAD, Feb 8: Minister for Water and Power Chaudhry Ahmed Mukhtar on Friday told the upper house of the Parliament that the world’s largest earth and rock filled Tarbela Dam constantly faced natural and man-made threats.

Replying to questions from senators the minister said that at present two types of sinkholes had developed at the main dam blanket (concrete material at the foundation of the dam) to prevent seepages through the several hundred feet deep highly pervious alluvial deposits.

The Minister did not give details of the depths and diameters of the sinkholes (natural depressions or holes in the earth’s surface caused by dissolution of surface material/layer forming gradually or suddenly) in the concrete bottom.

“However, the sinkholes at the main dam blanket have been treated by dumping the specified material on sinkhole locations through large boats (barges). The sinkholes have been treated by injecting specified impervious fine grained material,” Chaudhry Ahmed Mukhtar explained to the House.

According to the minister, an efficient observation system was working to cope with emergent situations and future developments.

The Minister said to date more than 500 sinkholes had appeared on the surface of the dam.

According to the former chairman of the Indus River System Authority (ISRA), Bashir Dahar, sinkholes were not big threats.

“But for a very large dam like the Tarbela, it is extremely important to monitor the behaviour of various structures to ensure their proper functioning and safety,” said the dam expert.

The minister also told the members that an estimated 200 million tons of sediment entered the lake/reservoir every year.

“This reduces the storage capacity of the reservoir by more than 32 per cent. Water to Tarbela largely comes from glacier melt. The soil particles in flowing water settle in the reservoir as they enter the stagnant water,” the Minister elaborated.

The minister said the government was working on two solutions: minimum conservation level of water should be raised from 1,300 feet to 1,378, while second viable solution to the silt problem was pending as the government in collaboration with a foreign consultant was yet to devise and provide an efficient Sediment Management System.

The members drew Chaudhry Ahmed Mukhtar’s attention to the terror threats to the dam located on the border of Khyber Pakhtunkhwa and Punjab.

According to the minister, nearly 5, 000 Rangers personnel were deployed at the project site to counter any unnecessary activity/threat.

“Four additional surveillance systems have been deployed to record the movement at check posts and important location,” the minister said adding that seven additional checkposts were under construction to restrict as well as monitor civilian movement besides installing electric gadgets to monitor activities in the area.