Tarbela Dam (, ) is an earth-filled dam along the Indus River in Pakistan's Khyber Pakhtunkhwa province. It is located mainly in the Haripur District of the province. It is about from the city of Haripur, northwest of Islamabad, and east of Peshawar. It is the largest earth-filled dam in the world. The dam is high above the riverbed and its reservoir, Tarbela Lake, has a surface area of approximately .
The Tarbela Dam is built on the Indus at Bara near the village of Tarbela. It is about 30 km from the town of Attock. When the Indus leaves the Himalayans foothills and enters the Potwar pleateau, the water is stored in the reservoir of the dam. It is 143 meters high, having an area of 243 square km. It has a storage capacity of 119 billion cubic meters of water and has nine gates to control the outflow of water. The dam was completed in 1976 and was designed to utilize water from the Indus River for irrigation, flood control, and the generation of hydroelectric power by storing flows during the monsoon period while subsequently releasing stored water during the low flow period in winter. The installed capacity of the 4,888 MW Tarbela hydroelectric power stations will increase to 6,418 MW after completion of the planned fifth extension financed by Asian Infrastructure Investment Bank and the World Bank.
Project description
The dam is at a narrow spot in the Indus River valley, named after the town of Tarbela in the Haripur District of the Hazara Division within the Khyber Pakhtunkhwa province of Pakistan.
The main dam wall, built of earth and rock fill, stretches from the island to river right, standing high. A pair of concrete auxiliary dams spans the river from the island to river left. The dam's two spillways are on the auxiliary dams rather than the main dam. The main spillway has a discharge capacity of and the auxiliary spillway, . Annually, over 70% of water discharged at Tarbela passes over the spillways and is not used for hydropower generation.
Five large tunnels were constructed as part of the outlet works. Hydroelectricity is generated from turbines in tunnel 1 through 3, while tunnels 4 and 5 were designed for irrigation use. 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 long, with a surface area of . The reservoir initially stored of water, with a live storage of , though this figure has been reduced over the subsequent 35 years of operation to due to silting. The maximum elevation of the reservoir is above MSL and the minimum operating elevation is above MSL. The catchment area upriver of the Tarbela Dam is spread over 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.
Background
Tarbela Dam was constructed as part of the Indus Basin Project after signing of the 1960 Indus Waters Treaty between India and Pakistan. The purpose was to compensate for the loss of water supplies of the eastern rivers (Ravi, Sutlej and Beas) that were designated for exclusive use by India per terms of the treaty. By the mid-1970s, power generation capacity was added in three subsequent hydro-electrical project extensions which were completed in 1992, installing a total of 3,478 MW generating capacity.
Construction
Construction of Tarbela Dam was carried out in three stages to meet the diversion requirements of the river. Construction was undertaken by the Italian firm Salini Impregilo.
Stage 1
In the first stage, the Indus River was allowed to flow in its natural channel, while construction works commenced on the right bank where a long and wide diversion channel was being excavated along with a high buttress dam that was also being constructed. Stage 1 construction lasted approximately 2.5 years.