Talking to APP, Wapda officials said the study was being conducted to tackle the issue of decreasing water storage capacity in the largest reservoir, caused by sedimentation. These sediments have not only decreased the storage capacity of the reservoir but are also posing a serious threat to the powerhouse structures and machines.
The live storage capacity of Tarbela Dam has been reduced by 30 per cent during the last 36 years due to sedimentation. From its original storage capacity of 9.68 million acre feet (MAF), the storage capacity reduced to 6.77 MAF in 2010.
The officials said that besides exploring ways to flush the sediments out of the reservoir, the study also aims at determining its impact on the downstream irrigation infrastructure. Wapda officials said that five international consultancy firms had been short-listed, which will soon be asked to submit technical and financial proposals for the study.
Earlier, Wapda had carried out five studies on the sediment management of the dam. The recent study was recommended by Dr George W Annandale, a well-known expert on sedimentation, in the fifth periodic Inspection and the Task Force created in Wapda, in cooperation with the International Commission on Irrigation and Drainage.
Tarbela Dam, an engineering marvel built in 1974, is considered to be the lifeline for the national economy. It spreads over an area of 259 square kilometres, with maximum elevation of 1,550 feet above sea level.
Average annual water inflow at Tarbela is 64 MAF, which brings along a huge quantum of sediments estimated at 200 million tons per year from a catchment area of more than 169,000 square kilometres.
Published in The Express Tribune, December 15th, 2010.
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