Tarbela Dam (Urdu/Pashto:تربیلا بند) on the Indus River in Pakistan is the largest earth filled dam in the world and 5th largest by structural volume.[2][3][4] It is named after the town Tarbela, in Khyber Pakhtunkhwa, about 50 kilometres (31 mi) northwest of Islamabad. The dam is 485 feet (148 m) high above the riverbed. The dam forms the Tarbela Reservoir, with a surface area of approximately 250-square-kilometre (97 sq mi). The dam was completed in 1976 and was designed to store water from the Indus River for irrigation, flood control, and the generation of hydroelectric power.[5]
The project is located at a narrow spot in the Indus River valley, at Tarbela between Haripur District and Swabi District, approximately 60 kilometers northwest of Islamabad.
The main dam wall, built of earth and rock fill, stretches 2,743 metres (8,999 ft) from the island to river right, standing 148 metres (486 ft) high. A pair of concrete auxiliary dams spans the river from the island to river left. The dam's two spillways are located on the auxiliary dams rather than the main dam. The main spillway has a discharge capacity of 18,406 cubic metres per second (650,000 cu ft/s) and the auxiliary spillway, 24,070 cubic metres per second (850,000 cu ft/s). Annually, over 70% of water discharged at Tarbela passes over the spillways, and is not used for hydropower generation.[6]
Five large tunnels were constructed as part of Tarbela Dam's outlet works. Hydroelectricity is generated from turbines in tunnel 1 through 3, while tunnels 4 and 5 were designed for irrigation use, although both tunnels are to be converted to hydropower tunnels to increase Tarbela's electricity generating capacity.These tunnels were originally used to divert the Indus River while the dam was being constructed.
MA hydroelectric power plant on the right side of the main dam houses 14 generators fed with water from outlet tunnels 1, 2, and 3. There are four 175 MW generators on tunnel 1, six 175 MW generators on tunnel 2, and four 432 MW generators on tunnel 3, for a total generating capacity of 3,478 MW.
Tarbela Reservoir is 80.5 kilometres (50.0 mi) long, with a surface area of 250 square kilometres (97 sq mi). The reservoir initially stored 11,600,000 acre feet (14.3 km3) of water, with a live storage of 9,700,000 acre feet (12.0 km3), though this figure has been reduced over the subsequent 35 years of operation to 6,800,000 acre feet (8.4 km3) due to silting.
The catchment area upriver of the Tarbela Dam is spread over 168,000 square kilometres (65,000 sq mi) of land largely supplemented by snow and glacier melt from the southern slopes of the Himalayas. There are two main Indus River tributaries upstream of the Tarbela Dam. These are the Shyok River, joining near Skardu, and the Siran River near Tarbela.
