LAHORE, March 12: Pakistan has lost 24 per cent of water storage capacity and its reservoirs can now hold only 11.38 million acre feet water against a capacity of 15.02maf, according to a survey of dams.

A survey of Tarbela dam has been an annual feature since 1981, whereas Mangla dam’s survey is conducted every three to five years because of little silt moving into the lake. According to the survey, Tarbela dam, which was completed three decades ago, had a gross capacity of 11.62maf and live (usable) capacity of 9.68maf, with 1.94maf water left in the lake (dead level) to check silt movement.

In 1979, Tarbela lost 3.3 per cent storage and its live storage capacity dropped to 9.36maf. In 1990, the loss came to 10.6 per cent, with storage dropping to 8.65maf. In 2000, the live storage dropped to 7.97maf a total loss of 17.7 per cent. In 2007, the loss has gone up to a whopping 24.07 per cent, with total capacity dropping to 7.35maf.

The loss at Tarbela was further aggravated by the raising of the dead level, which caused another loss of 0.511maf. The live storage thus further came down to 6.84maf from 7.35maf.

At Mangla, the live storage capacity has come down to 4.54maf against the original 5.34maf in 1967 when the dam was built. The loss has remained limited because of slow movement of silt in the lake and the dead level remaining the same over the past 40 years. The two dams had in the beginning a combined capacity of 15.02maf, which has now declined to 11.36maf. The cumulative loss at the dams has thus increased to 3.64maf or 24 per cent.