LAHORE, Aug 3: The combined rivers flow dipped to a record 30-year low during the last week of July, forcing the Indus River System Authority on Saturday to reduce supply to provinces by 22 per cent aimed at refilling the Tarbela Dam.

An official of the water and power ministry said that Irsa had been liberal in releasing water to provinces during June and July.

This liberal distribution brought down the shortage from the previously calculated 22pc to 11.8pc for Punjab and 12.6pc for Sindh. However, he added, it also created a problem as far as the Tarbela Dam filling was concerned unless Irsa changed it behaviour which Irsa did on Saturday.

Irsa prepares a filling pattern for Tarbela in the beginning of every Kharif season, sources in Irsa said. It takes both maximum and minimum inflows while calculating the filling formula.

Current calculations show that in case of maximum inflows the lake should have touched the 1,531-foot mark by July 31, storing around 6maf (million acre feet) of water. The corresponding outflow in this case should have been 150,000 cusecs.

According to the minimum water inflow scenario, the dam should have been at 1,488 feet, housing around 3.5maf water, and corresponding outflow should have been 90,000 cusecs.

But on July 31, the lake was only at 1,484 feet; about four feet below the minimum level. This occurred despite the fact that inflows this year were maximum.

The situation panicked Irsa authorities, who are now trying to refill the lake through every possible way, sources said, adding that a month of high temperature was still left and the dam could be filled but only if Irsa became miser with supplies and withstood any executive order.

On the other hand, the reduction in supply can bring corresponding harm to the cotton crop which is nearing the maturity stage, an official of the Farmers Associates of Pakistan said.

The crop in both provinces cannot afford any shortage at this stage. Though Irsa wanted a further cut, Punjab pleaded the case of cotton crop and seemed to have convinced Irsa, he added.

A reduced release from the Indus arm and less supply in Chenab forced Punjab to increase it supplies from the Mangla Dam from 17,000 cusecs to 25,000 cusecs, keeping its lake level constant at 1,197 feet for the last many days.

The Mangla lake is only 4.5 feet below its optimum level which is not as great a matter of concern as Tarbela, a Wapda official said. There are still two months of monsoon left and the dam could be filled during this period. Besides, the meteorological department has predicted normal rain this year. If snow-melt fills 80pc of the dam by June 20, the rest could be filled by the rain.

On Saturday, the Tarbela lake stood at 1,485.7 feet. It had stored 3.813maf water. Last year, on the corresponding day, the dam level was 1,519.60 feet with 5.479maf water — and it was a drought year. Indus river had an inflow of 140,800 cusecs and outflow of 135,000 on Saturday.

The Mangla level was 1,197.50 feet with 4.363maf water. Its inflow was 18,600 cusecs and outflow 25,000 cusecs.

On the corresponding day last year, the lake level was at 1,169.20 feet.

Tarbela and Mangla lakes have a capacity of 7.2maf and 4.46maf water, respectively.