Biggest dam of Pakistan, Tarbela dam

A power station was constructed at the right bank of the main dam. Ten units each with an installed generating capacity of 175 MW were installed on tunnels 1 and 2 by 1985. Four units each with an installed generating capacity of 432 MW on tunnel 3 were commissioned in June 1994 while three units each having a generating capacity of 470 MW were installed on tunnel 4 which was commissioned in March 2018. Total generation of Tarbela enhanced to 4888 MW with the addition of T4th Ext. HPP constitutes about 50% of hydel generation in Pakistan. Tarbela reservoir is 60 Miles long, 100 square miles in area, and had initially a gross storage capacity of 11.62 MAF and a live storage capacity is 9.68 MAF. The total catchment area is 65,50p sq miles. Four main tributaries join the Indus river, Shyok river at an elevation of 8,000 feet above sea level near Skardu, Gilgit, and Hunza rivers join near Bunji and Siran river just north of Tarbela. The creation of the reservoir required the evacuation of 120 villages and the displacement of 96,000 persons. This task was accomplished by playing cash compensation for their land and built-up properties and providing alternate agricultural land to the owners in the Punjab and Sindh provinces. Total amount spent on resettlement is one billion rupees. Five townships with 12,000 residential plots and 1,500 commercial plots were constructed for the affectees around the reservoir. The Auxiliary spillway is similar in design to the service spillway but with a discharge capacity of 8,50,000 cusecs (24,070 cusecs). The service spillway having 44 per cent of the total capacity is sufficient to pass all but very rare floods. Its maximum discharge capacity is 65,000 cusecs. In March 2012, a fourth extension was approved to install a power plant of 1,410 MW on the fourth tunnel. The objective of the Tarbela Fourth Extension Hydropower Project (T4HP) is to add 1,410 Megawatt (MW) of renewable and low-cost electricity to Tarbela Dam's generation capacity during the high-demand summer season. The project has installed a power plant of 1,410 MW on the fourth tunnel at Tarbela Dam.

The Tarbela Fifth Extension Hydropower Project will install an additional power plant at Tunnel 5. This is expected to bring the total generation capacity of Tarbela to 6,298 MW (nearly 20 percent of the current installed capacity in the country). The expansion of the Tarbela dam was designed in stages. In 1980, the first four units were added to Tunnel 1 with an installed capacity of 700 MW. The second extension increased this to 1,750 MW in 1985 through the addition of 6 units to Tunnel 2. The third extension, adding 3 units of 432 MW in 1993, increased capacity to 3,478 MW. In March 2012, a fourth extension was approved to install a power plant of 1,410 MW on the fourth tunnel. The power plant became operational in 2018, increasing the dam's installed capacity to 4,888 MW. A fifth extension under implementation will finance the installation of a plant of 1,410 MW on Tunnel 5 and a 50- kilometer transmission line to transport electricity to the national grid. Once completed, the total capacity of Tarbela will be 6,298 MW. Tarbela reservoir during flow periods has released an average of 8.186 MAF of water since 1975_2022 to irrigate 22 Million Acres (8.9 Million hectares) of agricultural land in all provinces of Pakistan. The benefits of these releases amount to PKR 231.142 Billion. In addition to water benefits,549 billion units of low cost/environmentally friendly clean hydel energy have been generated through the installed capacity of 4,888 MW of Tarbela Power units (1_17). The overall Water and power benefits accrued from the project have been estimated at PKR 905.15 billion.