Tarbela Dam

Tarbela Dam (Pashto: د توربېلې بند, Hindko: تربیلا بند) 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.[1] It is about 20 km (10 mi) from the city of Haripur, 105 km (65 mi) northwest of Islamabad, and 125 km (80 mi) east of Peshawar. It is the largest earth-filled dam in the world.[2][3][4] The dam is 143 metres (470 ft) high above the riverbed and its reservoir, Tarbela Lake, has a surface area of approximately 250 square kilometres (97 sq mi).

Tarbela Dam
Aerial view of the dam and Tarbela Lake reservoir
Tarbela Dam is located in Pakistan
Tarbela Dam
Location of Tarbela Dam in Pakistan
Tarbela Dam is located in Khyber Pakhtunkhwa
Tarbela Dam
Tarbela Dam (Khyber Pakhtunkhwa)
Official nameTarbela Dam
LocationHaripur, Khyber Pakhtunkhwa, Pakistan
Coordinates34°05′23″N 72°41′54″E
PurposeWater Storage, Power Generation
StatusOperational
Construction began1968
Opening date1976 (1976)
Construction cost2.85 Billion USD
Owner(s)Government of Pakistan
Operator(s)Water and Power Development Authority
Dam and spillways
Type of damEarth and rock filled dam
ImpoundsIndus River
Height (foundation)470 feet (143 m)
Height (thalweg)485 feet (148 m)
Length9,000 feet (2,743 m)
Dam volume139,000,000 cu yd (106,000,000 m3)
Spillways16 ( 7 Service + 9 Auxiliary)
Spillway capacityService 650,000 cusecs + Auxiliary 850,000 cusecs
Reservoir
CreatesTarbela Reservoir
Total capacity11,620,000 acre⋅ft (14.33 km3) (1974)
Active capacity9,679,000 acre⋅ft (11.939 km3) (1974)
Inactive capacity1,941,000 acre⋅ft (2.394 km3) (1974)
Catchment area65,500 sq mi (170,000 km2)
Surface area100 sq mi (260 km2)
Maximum water depth450 ft (140 m)
Normal elevation1,464 ft (446 m)
Power Station
Commission date1977–1982
Turbines10 × 175 MW
4 × 432 MW
3 × 470 MW
Installed capacity4,888 MW
Annual generation17,395 GWh (2020)

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[5] 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.[6]

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.

Tarbela Lake was formed as a reservoir behind a dam

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 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.[7]

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 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 maximum elevation of the reservoir is 1,550 ft (470 m) above MSL and the minimum operating elevation is 1,392 ft (424 m) above MSL. 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.

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.[8] 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
Generators in the Tarbela Dam

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.[9]

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 1,500 feet (460 meters) long and 694.8 feet (211.8 meters) wide diversion channel was being excavated along with a 105 feet (32 meters) high buttress dam that was also being constructed. Stage 1 construction lasted approximately 2.5 years.

Stage 2

The main embankment dam and the upstream blanket were constructed across the main valley of the river Indus as part of the second stage of construction. During this time, water from the Indus river remained diverted through the diversion channel. By the end of construction works in stage 2, tunnels had been built for diversion purposes. Stage 2 construction took 3 years to complete.[10]

Stage 3

Under the third stage of construction, works were carried out on the closure of diversion channel and construction of the dam in that portion while the river was made to flow through diversion tunnels. The remaining portion of upstream blanket and the main dam at higher levels was also completed as part of stage 3 works, which were concluded in 1976.[10]

Re-settlement of people affected by Tarbela Dam

An area of about 260 square kilometers and about 82,000 acres (33,000 ha) of land was acquired for construction. The large reservoir of the dam submerged 135 villages, which resulted in displacement of a population of about 96,000 people,[11] many of whom were relocated to townships surrounding the Tarbela Reservoir or in adjacent higher valleys.[12]

For the land and built-up property acquired under the Land Acquisition Act of 1984, a cash compensation of Rs 469.65 million was paid to those affected. In the absence of a national policy, the resettlement concerns of the people displaced by the Tarbela Dam were addressed on an ad hoc basis. In 2011, many such people had still not been resettled or given land in compensation for their losses by the government of Pakistan, in accordance with its contractual obligations with the World Bank.[13]

Lifespan

Because the source of the Indus River is glacial meltwater from the Himalayas, the river carries huge amounts of sediment, with an annual suspended sediment load of 200 million tons.[14] Live storage capacity of Tarbela reservoir had declined more than 33.5 per cent to 6.434 million acre feet (MAF) against its original capacity of 9.679 MAF because of sedimentation over the past 38 years.[15] The useful life of the dam and reservoir was estimated to be approximately 50 years. However, sedimentation 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.[16]

Pakistan plans to construct several large dams upstream of Tarbela, including the Diamer-Bhasha Dam. Upon completion of the Diamer-Bhasha dam, sediment loads into Tarbela will be decreased by 69%.[17]

Project benefits

In addition to fulfilling the primary purpose of the dam, i.e., supplying water for irrigation, Tarbela Power Station has generated 341.139 billion kWh of hydro-electric energy since commissioning. A record annual generation of 16.463 billion kWh was recorded during 1998–99. Annual generation during 2007–08 was 14.959 billion kWh while the station shared peak load of 3702 MW during the year, which was 23.057% of total WAPDA system peak.[18]

Tarbela-IV Extension Project

Tarbela dam extension-IV was planned in June, 2012, and PC-1 was developed for the project. US ambassador Richard Olson offered aid for construction of this project during his visit to Pakistan, in March, 2013.[19] In September 2013, Pakistan's Water and Power Development Authority signed a Rs. 26.053 billion contract with Chinese firm Sinohydro and Germany's Voith Hydro for executing civil works on the 1,410 MW Tarbela-IV Extension Project.[20] Construction commenced in February 2014,[21] and was completed in February 2018.[22]

This project was constructed on Tunnel No. 4 of Tarbela Dam. It consists of three turbine-generator units, each with a capacity of 470 MW. The project is expected to provide an average of 3.84 billion units of electricity annually to the National Grid. It is intended to help supplement electricity supply during the high-demand summer months.

Annual benefits of the project were estimated at Rs. 30.7 billion.[23] On an annual basis, over 70% of water passing through Tarbela is discharged over spillways, while only a portion of the remaining 30% is used for hydropower generation.[7]

The Water and Power Development Authority in Pakistan says the third and last unit at its 1,410-MW Tarbela 4th Extension Hydropower Project has been synchronized with the National Grid. With this extension, the installed capacity of the Tarbela Hydel Power Station has increased to 4,888 MW.[24]

Financing

The project's cost was initially estimated to be $928 million,[23] but the cost was revised downwards to $651 million.[25] The World Bank had agreed to provide an $840 million loan for the project in June 2013.[26]

The loan had two components: The first is a $400 million International Development Association loan,[27] which will be lent as a concessional loan at low interest rates.[28] The second portion consists of a $440 million from the World Bank's International Bank for Reconstruction and Development.[27] Pakistan's Water and Power Development Authority was to provide the remaining $74 million required for construction,[29] before the project's cost was downwardly revised by $277 million. Interest costs for the loans are estimated to cost $83.5 million.[30]

Because of revised lower costs to $651 million from $928 million, the World Bank permitted Pakistani officials to expedite completion of the project by 8 months at a cost of an additional $51 million.[31] Pakistani officials were also permitted to divert $126 million towards the Tarbela-V Extension Project.[31]

Tarbela-V Extension Project

The Tarbela Dam was built with five original tunnels, with the first three dedicated to hydropower generation, and the remaining two slated for irrigation use. The fourth phase extension project uses the first of the two irrigation tunnels, while the fifth phase extension will use the second irrigation tunnel.[32] Pakistan's Water and Power Development Authority sought expressions of interest for the Tarbela-V Extension Project in August 2014,[33] and was given final consent for construction in September 2015.[32]

The hydro power project of tunnel 5 has two major components: power generation facilities and power evacuation facilities. The major works included under the project are modifications to tunnel 5 and building a new power house and its ancillaries to generate about 1,800GWh of power annually, a new 50 km of 500kV double-circuit transmission line from Tarbela to the Islamabad West Grid Station for power evacuation, and a new 500kV Islamabad West Grid Station.

Construction commenced in August 2021 and will require an estimated 3.5 years for completion. The project will require installation of three turbines with a capacity of 510 MW each in Tarbela's fifth tunnel which was previously dedicated to agricultural use. Upon completion, the total power generating capacity of Tarbela Dam will increase to 6,418 MW.[34][35]

Financing

In November 2015, the World Bank affirmed that it would finance at least $326 million of the project's estimated $796 million cost[32] which includes $126 million of funding that was diverted from the $840 million fourth phase extension project after costs for that project were revised downwards.[32] In September 2016, the World Bank approved an additional financing of $390 million for the fifth extension hydropower project of Tarbela dam that will support the scaling up of the power generation capacity by adding 1,530 megawatts to the existing tunnel 5.

The project will be financed by the International Bank for Reconstruction and Development (IBRD), with a variable spread and 20-year maturity, including a six-year grace period. This will be the first World Bank-supported project in South Asia to be jointly financed with the Asian Infrastructure Investment Bank (AIIB) which will be providing $300m and the Government of Pakistan $133.5m. The total cost of the project is $823.5m.

See also
Wikimedia Commons has media related to Tarbela Dam.

Notes
  1. Tarbela Dam. WAPDA.
  2. Asianics Agro-Dev. International (Pvt) Ltd. (2000). Tarbela Dam and related aspects of the Indus River Basin, Pakistan (PDF) (Report). Cape Town: World Commission on Dams. Archived from the original (PDF) on 2010-06-13. Retrieved 2010-10-28.
  3. Earth Sciences Web Team. "Tarbela Dam, Pakistan". Earth Observatory. National Aeronautics and Space Administration. Archived from the original on 2010-07-15. Retrieved 2010-10-28.
  4. "Tarbela Dam". PakistanPaedia. 2006-08-07. Retrieved 2012-01-26.
  5. Rodney White (1 January 2001). Evacuation of Sediments from Reservoirs. Thomas Telford Publishing. pp. 163–169. ISBN 978-0727729538. Retrieved 4 August 2013.
  6. "Tarbela 5th extension project to generate electricity by 2025". 20 May 2023. Retrieved 31 May 2023.
  7. "PROJECT APPRAISAL DOCUMENT ON A PROPOSED LOAN IN THE AMOUNT OF US$400 MILLION AND Report No: 60963-PK PROPOSED CREDIT IN THE AMOUNT OF 283.7 MILLION SDRS (US$440 MILLION EQUIVALENT) TO THE ISLAMIC REPUBLIC OF PAKISTAN FOR THE TARBELA FOURTH EXTENSION HYDROPOWER PROJECT (T4HP)" (PDF). World Bank. Retrieved 23 March 2016. Annually, over 70 percent of the water is spilled over the spillway instead of generating hydropower.
  8. "History". Retrieved 30 August 2016.
  9. "Tarbela Dam Project, Haripur District, Pakistan". Water Technology. Retrieved 24 March 2016.
  10. "Tarbela Dam". WAPDA. Retrieved 23 March 2016.
  11. Terminski, Bogumil (2013). "Development-Induced Displacement and Resettlement: Theoretical Frameworks and Current Challenges", Indiana University
  12. "Pakistan: Tarbela dam". Retrieved 30 August 2016.
  13. "Settlement of Tarbela Dam affectees claims". Pakistan & Gulf Economist. Archived from the original on 30 July 2020. Retrieved 12 April 2011.
  14. Roca, M. "Tarbela Dam in Pakistan. Case study of reservoir sedimentation" (PDF): 1. Archived from the original (PDF) on 23 November 2015. Retrieved 24 March 2016. {{cite journal}}: Cite journal requires |journal= (help)
  15. "Another $51m to expedite Tarbela project completion". 7 March 2015. Retrieved 30 August 2016.
  16. Lorrai, C and Pasche, N. 'Tarbela Dam-Case Study' Swiss Federal Institute of Technology Zurich: April 2007
  17. Roca, M. "Tarbela Dam in Pakistan. Case study of reservoir sedimentation" (PDF): 7. Archived from the original (PDF) on 23 November 2015. Retrieved 24 March 2016. {{cite journal}}: Cite journal requires |journal= (help)
  18. "WAPDA - Power Generation". Archived from the original on 2012-03-07. Retrieved 2014-03-29.
  19. "US to provide $25m for Tarbela dam extension". The Dawn. 2013-03-06.
  20. "Rs26 billion Tarbela dam extension plan". Dawn. 10 September 2013. Retrieved 10 September 2013.
  21. "Tackling energy crisis: Nawaz inaugurates Tarbela-IV project". The Express Tribune. 26 February 2014. Retrieved 23 March 2016.
  22. "Tarbela 4th extension project starts power production - The Express Tribune". The Express Tribune. 2018-02-27. Retrieved 2018-02-27.
  23. "Wapda inks MoU for 1410MW Tarbela 4th Extension Project". The Nation (Pakistan). 10 September 2013. Retrieved 10 September 2013.
  24. "WAPDA announces 1,410-MW Tarbela 4th Extension Hydropower Project completed". Archived from the original on 2019-01-30. Retrieved 2018-10-19.
  25. "Another $51m to expedite Tarbela project completion". Dawn. 7 March 2015. Retrieved 23 March 2016. The original T4 project was estimated to cost $928m, but the project authorities had been able to conclude the project contract at $651m.
  26. "World Bank to provide $840m for Tarbela extension". Pakistan Today. 13 June 2013. Retrieved 10 September 2013.
  27. World Bank (20 March 2012). "Pakistan: Tarbela Fourth Extension Hydropower Project Specific Investment Loan SUMMARY OF DISCUSSION" (PDF). Retrieved 23 March 2016. Executive Directors approved a Tarbela Fourth Extension Hydropower Project Loan and Credit for the Islamic Republic of Pakistan in the amount of US$440 million equivalent (IDA Credit) and US$400 million (IBRD loan) respectively on the payment terms and conditions set out in the President's Memorandum (R2012-0036 [IDA/R2012- 0044]).
  28. "What is IDA?". World Bank. Retrieved 23 March 2016. IDA lends money on concessional terms. This means that IDA credits have a zero or very low interest charge and repayments are stretched over 25 to 38 years, including a 5- to 10-year grace period. IDA also provides grants to countries at risk of debt distress.
  29. "PROJECT APPRAISAL DOCUMENT ON A PROPOSED LOAN IN THE AMOUNT OF US$400 MILLION AND Report No: 60963-PK PROPOSED CREDIT IN THE AMOUNT OF 283.7 MILLION SDRS (US$440 MILLION EQUIVALENT) TO THE ISLAMIC REPUBLIC OF PAKISTAN FOR THE TARBELA FOURTH EXTENSION HYDROPOWER PROJECT (T4HP)" (PDF). World Bank. Retrieved 23 March 2016. The Project would be financed by an IBRD loan of US$400 million, an IDA Credit of US$440 million equivalent, and WAPDA financing of US$74.0 million
  30. "PROJECT APPRAISAL DOCUMENT ON A PROPOSED LOAN IN THE AMOUNT OF US$400 MILLION AND Report No: 60963-PK PROPOSED CREDIT IN THE AMOUNT OF 283.7 MILLION SDRS (US$440 MILLION EQUIVALENT) TO THE ISLAMIC REPUBLIC OF PAKISTAN FOR THE TARBELA FOURTH EXTENSION HYDROPOWER PROJECT (T4HP)" (PDF). World Bank. Retrieved 23 March 2016. ...and Interest During Construction (IDC) of US$83.5 million, assuming IBRD and IDA terms for the loan.
  31. "Another $51m to expedite Tarbela project completion". Dawn. 7 March 2015. Retrieved 23 March 2016. Since the project cost was much lower than estimates finalised in consultation with the World Bank ($840m), the bank not only approved $51m acceleration programme, but also agreed to divert about $150m, saving another 1,400MW for Tarbela 5th Extension project which is expected to be completed by June 2018.
  32. Harris, Michael (2 October 2015). "Pakistan's 1,300-MW Tarbela 5th Extension hydropower project receives next-to-last approval". Hydroworld. Retrieved 23 March 2016.
  33. "Pakistan extends consultant call for 1,300-MW Tarbela Dam 5th Extension". Hydroworld. 19 August 2014. Retrieved 23 March 2016.
  34. "PM breaks ground for US $ 807 million Tarbela 5th Extention Hydropower project". 12 August 2021. Retrieved 30 May 2023.
  35. "Tarbela 5th extension project to generate electricity by 2025". 20 May 2023. Retrieved 30 May 2023.
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