Tarbela Dam

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Tarbela Dam has a reservoir size of some 95 sq mi (250 km2) makes it the largest earth filled dam in the world. The dam was completed in 1974 and was designed to store water from the Indus River for irrigation and flood control, and for the generation of hydro-electric power.

The reservoir is 50 miles (80.5 km) long 100 square, miles (260 square kilometers) in area and has a gross storage capacity of 11.6 MAF (17.109 million cu. Meters) with a live storage capacity of 9.7 MAF (14,307 million cu. Meters). The total catchment area above Tarbela is spread over 65,000 sq. miles (168,000 sq. kilometers) which largely brings in snowmelt supplied in addition to some monsoon rains. Tarbela Dam is a large dam on the Indus River in Pakistan located in Haripur district of Hazara Division of North-West Frontier Province about 50 km (31 mi) northwest of Islamabad, at height of 485 ft (148 m) above the river bed.

On May 14, 1968, the World’s largest single contract for the construction of civil works at that time, the Tarbela Dam Project was signed at a price of RS.2,965,493,217 ($ 623 Million) between the Water and Power Development Authority of Pakistan and the Tarbela Dam Joint Venture which comprised a group of three Italian and three French heavy construction contractors. Later five German and two Swiss contractors also joined the group making up a consortium of thirteen European firms led by Italian firm namely Impregilo.

Its main spillway has a discharge capacity of 650,000 cusecs (18,406 cumecs) and auxiliary spillway 850,000 cusecs (24,070 cusecs). A group of 4 tunnels (each half a mile long), through the right abutment rock have been constructed for irrigation releases and power generation. During the construction operations, these tunnels were used initially for river diversion. Irrigation tunnel 5 situated on the left bank, for which NESPAK were the Project Consultants, was put into operation in April 1976.

A power station on the right bank near the toe of the main dam houses fourteen(14), power units, out of which 4 units, each with installed generating capacity of 175 MW are installed on tunnel 1, 6 units (NO.5 to 10), 175 MW each on tunnel NO.2 and 4 Units ( NO.11-14) of 432 MW each on Tunnel 3, thus making total generating capacity of Tarbela Power Station as 3478 MW.

Because the source of the Indus River is glacial meltwater from the Himalayas, the river carries huge amounts of sediment. The annual suspended sediment load is about 430 million tons per year. This means that, over time, the reservoir will fill. The useful life of the dam and reservoir was estimated to be somewhere around fifty years, since the dam's completion in 1976, meaning that the reservoir would have been full of sediment by 2030.

Sedimentation, however, has been much lower than predicted, and it is now estimated that the useful lifespan of the dam will be 85 years, to about 2060.