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Restructuring Tarbela.

Article Excerpt
Should Tarbela be with WAPDA? The answer is no, Tarbela was constructed as part of the Indus Basin Treaty to provide storage of 9.4 MAF. Tarbela makes a major contribution to the national economy.

It provides nearly 30 percent of all the irrigation water available in dry season, 2100 MW of hydropower was to be generated as a by-product. By the year 1992, the generating capacity was raised to 3428 MW, with the 3rd extension comprising four more units of 432 MW capacity each.

In the original operating rule, stipulated by the designers, the 'Minimum Operating Level' (MOL) of the reservoir level was mandated to be lowered to 396 meters (1300 feet) for a month between May 20 through June 20 every year, before being raised to 492 meters (1550 feet). This rule was designed to ensure optimum condition for effectively flushing out the sediments through tunnels 3 and 4. As long as this rule was diligently followed, the delta formed by the sediments moved slow by towards the dam at an average rate of one mile per annum.

In November 1989 (MOL) of the dam was raised to 408 meters 1339 feet). This was done to overcome violent vibrations to 4 power units (No.5 to 8). This was also done in the hope of starting construction of Kalabagh to make up for loss of water resulting from the raising of its MOL. With this decision, WAPDA almost converted Tarbela from irrigation to a power project. From 1990 to mid 1996 WAPDA maximized the generation of electricity and as a result of good rains and more than normal water flows into the rivers, demand for irrigation was relatively less than normal....