Tarbela Dam: The World’s Largest Fill-type Dam
Tarbela Dam is the largest fill-type Dam in the world. It was built at the cost of $1.49bn on the Indus River near the small town of Tarbela in Haripur district, Khyber Pakhtunkhwa. The height of the Tarbela Dam is about 470 feet. The water storage capacity of the Tarbela dam is about 14.3 billion cubic meters.
Tarbela Dam is the second largest dam in the world in terms of storage capacity. In addition, a hydropower plant with an installed capacity of 3,478 million watts has been constructed on the right side of Tarbela Dam.
Completion of Project
Construction on the primary elements of the project was started in 1968 and initial operations of the dam started in 1978. The project was fully completed in 1984.
The project was executed by Water and Power Development Authority (WAPDA) on the behalf of the Govt. of Pakistan. Construction was carried out under a single civil works contract.
Major financial contribution for the project was given by the World Bank in the form of a bank loan and two international Development Association (IDA) credits. The bank loan was approved in 1968 and the two IDA credits were approved by 1978. The loans and credits were fully paid out by September 1981.
Increasing Life of Tarbela Dam
Pakistan is recently constructing the Diamer Basha dam on the river Indus which will increase the life of the Tarbela dam by 35 years. The new project is partly financed by the US.
Purpose and Need of Pakistan’s Dam Project
“The project was built by Tarbela Dam Joint Venture, which was led by Italian contractor Impregilo.”
Pakistan was entirely dependent on unregulated flows of the Indus River and her tributaries even after 20 years of her independence. The agricultural side was on the lower side due to a deficiency of water during the critical growing season. The main reason behind this problem was the seasonal variations in the river flow. Additionally, there were no storage reservoirs to conserve surplus flow.
Strengthening Irrigation System
In order to strengthen the irrigation System, the Pakistani Government, with assistance from the World Bank, embarked on the Indus Basin Project, which comprised two large dams. The first dam built under this water control project was the Mangla Dam on the Jhelum River and the other was Tarbela on the Indus River.
The primary purpose of the Tarbela Dam Project was to regulate the flows of the Indus River for irrigation use. Other objectives were to achieve the substantial generation of hydroelectric power and flood control by conserving snow melts and monsoon flows of the Indus River.
Components of the world’s largest fill-type dam
The Tarbela Dam project involved the construction of an earth and rock-fill dam on the River Indus and a power plant. The maximum height of the main embankment from the lowest foundation point is 470ft and the length is 9000 ft at its crest. The dam required 138 million cubic yards to fill.
“The Project was executed by Water and Power Development Authority (WAPDA) on behalf of the Government of Pakistan.”
The main embankment is flanked by the two auxiliary embankments on the left bank. The maximum height of one of the auxiliary embankments is 345ft, while that of the other is 220ft and the lengths at crest are 2340ft and 960ft respectively.
The two auxiliary embankments carry two spillways, the service spillway, and the auxiliary spillway. The service spillway is fitted with seven gates and has a discharge capacity of 650,000cusec. The auxiliary spillway with nine gates can discharge 850,000cusec.
Group of Four Tunnels
The valley wall on the right bank, at the upstream end, was cut through to build a group of four tunnels. Three of these tunnels were intended for hydro-power generation, while the fourth tunnel is used for irrigation releases.
The catchment area of the Tarbela Dam reservoir in Haripur District
The catchment area of the reservoir created by the dam is 169,600 sq. kilometers. The reservoir, with a maximum depth of more than 450ft. can impound up to an 11.2million acre-foot of water at the maximum lake elevation of 1,550ft. The net usable capacity of the reservoir is 9.68MAF.
The water is stocked during the months of June, July, and August when the river flow is at its maximum.
Tarbela Hydropower Plant near the Indus River
The Tarbela hydropower plant is constructed on the right side of the main embankment. It is installed with 14 power generating units and the water is fed from the outlet tunnels one, two, and three. The plant has a total installed capacity of 3.478MV.
Four generators of 175MW each on tunnel one were put into production in 1977. There are six 175MW generators on tunnel two, four of which were commissioned in 1982 and the remaining two in 1985. Four generators of 433MW each were installed in tunnel four in 1992.
Key Players Involved
The project was built by Tarbela Dam Joint Venture, which was led by Italian contractor Impregilo. The joint venture was a consortium of three Italian and three French heavy civil engineering contractors. Five German and two Swiss companies joined the consortium in 1969.
Members of Joint Venture
Members of joint Vneture led by Impregilo included,
- Costruzioni general Farsura
- Impresa Astaldi Estero
- Compagine de Constructions Internationales
- Compagnie Francaise d’Enterprises
- Societe de Construction de Batignolles
- Phillip Holzmann
- Starbag Bau
- Ed Zueblin
- C. Baresel
- Conrad Zschokke and losinger