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Tarbela Dam likely to fill to capacity in a week

The Tarbela reservoir is likely to attain its maximum conservation level of 1,550 feet above sea level in the next four to five days, provided the water inflows pattern in River Indus at Tarbela continues to be the same as last week’s, say official sources.

Filling of the reservoir to its optimum capacity will reduce the shortage of water for the upcoming crops in the rabi season when wheat is sown. Its filling will also help tackle the electricity shortfall in the country by generating additional cheap hydel electricity, officials say.

According to official data, the water level in Tarbela lake reached 1545.4 feet on Friday at 0600 hours, as mean water inflows of 24 hours at Tarbela were recorded at 185,800 cusecs and outflows were recorded at 156,500 cusecs, raising the water level by another foot during the last 24 hours. Presently 6.293 million acres feet (MAF) of water have been stored in the Tarbela lake. Earlier, by mid August this year, it had seemed quite probable that the Tarbela reservoir could not be filled to its maximum conservation level,On the back of low water inflows, . Officials have termed low temperature in the catchments of Tarbela Dam this summer a basic reason for poor hydrological conditions, resulting in slow glacial melting in the vast catchment area and partly for less rain in upstream areas of the dam.

However, the Water and Power Development Authority (Wapda) – the organisation responsible for operating the dam – utilised rule curve Q, the criterion that provides guidelines for filling the Tarbela reservoir. This rule curve was already devised at the time of operation after completion of the dam but is being followed this year for the first time due to peculiar hydrological conditions. This criterion proved helpful in filling the reservoir at a critical juncture.

According to this criterion, the reservoir was filled by five to six feet per day up to 1,530 feet, and by about two feet per day up to 1,540 feet. Above the 1,540 feet level, the reservoir is being filled at an average of one foot daily. During filling of the reservoir, various factors relating to the safety of Tarbela dam including pore pressure and seepage remained within the safe limits.

Since its operation in the mid 1970s, the Tarbela dam project has played a pivotal role in Pakistan’s economy. Despite the natural phenomenon regarding accumulation of silt in the reservoir during the last 38 years, live storage capacity of the dam still stands at a 6.557 MAF.

In addition to providing water for agriculture, Tarbela Power Station also generates more than 14 billion units of low-cost hydel electricity every year.

Mangla Dam with a raised water storage capacity of 7.392 MAF could not be filled to a maximum level of 1,242 feet due to very low inflows this year. Presently, only 3.567 MAF of water could be stored in the Mangla Dam on River Jhelum against a maximum conservation capacity of 7.392 MAF.

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