The shortage of electrical power at an affordable cost has long been identified as one of the main hurdles to the industrial and economical growth of Pakistan. The Water and Power Development Authority (WAPDA) has continually sought to maximise the country?s capacity for hydro power generation and reduce the ever-increasing burden of imported fuel.
An important project for the country is the 1450MW Ghazi Barotha hydro scheme, located west of the capital Islamabad. The project harnesses 74m of hydraulic head in a 63km stretch between the tailrace of the Tarbela dam and the conference of the Indus and Haro rivers, and has been designed to cause minimum environmental and social impact.
Ghazi Barotha consists of three main components: the barrage, the power channel and the power complex. The project will utilise the normal Tarbela dam releases to provide year-round maximum power generation during the daily hours of peak demand, including the months of May and June when Mangla and Tarbela are historically at their lowest.
Construction costs
When the project was approved for construction, the estimated total project cost was US$2.25B (World Bank, SAR, 1995 price levels). Latest estimates for the project out-turn costs are US$2.07B (at April 2003 price levels). The project has been funded by WAPDA, supported by the World Bank, Asian Development Bank, Japanese Bank for International Cooperation, Kreditanstalst fuer Wiederaufbau (KfW), European Investment Bank, and Islamic Development Bank.
The economic studies have demonstrated that the project forms part of the least-cost expansion of the Pakistan power system. The least-cost status of the project remains valid for the full range of sensitivity analyses performed. The project has highly favourable economic parameters.
The guiding principle of Ghazi Barotha has been to maintain close contact between the engineering planners, the environmental planners, social scientists, local community groups and NGOs, right from the feasibility stage to project construction. This process allowed the planning teams to identify and avoid, or mitigate all potentially serious adverse environmental, social and archaeological effects. The culmination of this colossal effort was the relocation of just 110 dwellings. Acquisition of cultivated land was also kept to an absolute minimum, and all villages, graveyards and shrines were avoided. The construction works employed some 13,500 local people and numerous local companies. Over the course of the construction, this influx of capital into the local economy has had a significant effect of improving the business opportunities and economic growth, particularly in the project area.
Design features
The barrage, located 7km downstream of Tarbela dam, provides a 71Mm3 storage pond, allowing for the re-regulation of the daily discharge from Tarbela dam, by diverting the flow into the power channel. The principal features include 20 standard bays, eight undersluices and eight headregulator bays, in addition to rim embankments, fuse plug and dividing island.
The Barrage is able to pass the design flood of 18,700m3/sec through the standard bays and undersluices at the normal pond level. The fuse plug has been provided to pass the extreme floods up to the capacity of the Tarbela dam?s spillway and tunnels equalling 46,200 m3/sec.
Ghazi Barotha currently holds the record for the biggest lined channel in the world. The channel is some 51.9km long, with concrete lining and design flow of up to 1600m3/sec at a water depth of 9m and a bottom width of 58.4m.
The power channel has a near contour alignment, with hills on the left side and the land naturally draining towards the Indus river on the right side. The power channel intercepts 53 nullahs (natural streams), of which 27 major nullahs have required separate water bridges (called superpassages) to take them across the channel. The remaining 15 minor nullahs are being discharged into the power channel through individual inlets, whilst one nullah passes underneath the channel through a culvert.
In addition to the 34 road bridges, including bridges for both the Islamabad-Peshawar motorway and the GT road, the power channel is also crossed by 12 pedestrian bridges.
The main railway line joining Rawalpindi to Peshawar required the construction of the second longest single span railway bridge to be built in Pakistan. This may well prove to be the last riveted bridge of its type ever to be constructed.
The power complex begins with two headponds, with a combined live storage capacity of approximately 25.5Mm3 ? sufficient flow capacity for the daily requirement of four hours peak generation. This means that in May and June, the scheme will provide peak production of 1450MW.
The five generating units in the power house are each fed by a 10.6m diameter steel lined penstock. Each of the five 290MW turbo-generators can take a peak flow of 460m3/sec.
Due to the special nature of this project, it has been necessary to provide a self-priming siphon spillway of 1600m3/sec capacity, with energy dissipation in a stilling basin and a baffle chute. The power transmission is through 500kV circuits to WAPDA?s national grid system.
The installed capacity is 1450MW, consisting of five units, each of 290MW. The units have a design flow of 400m3/sec at optimum gate opening and 460m3/sec at full gate opening for a design head of 69m.
The principal items of power equipment are as follows:
? Five 257/295MW Francis turbines, each with a 290MW generator, which together have a combined power generating efficiency of 94%.
? Five three-phase banks of transformers, each single-phase unit being 107.5MVA.
? 500kV conventional outdoor switchgear configured in one and a half breaker arrangement.
? Twelve cranes with lifting capacities from 6 to 450t.
Spread over such a large area, it was considered necessary both for safety and efficiency that monitor and control be handled centrally. This has been achieved by providing two independent distributed control systems (DCS) ? one each at the barrage and power complex, which share information through a fiber optic cable link.
The project was approved by the Government of Pakistan in June 1994. Preparatory works were started in mid 1995, initially with the acquisition of land, construction of the permanent colonies and a new access road to the power complex site.
Construction of the barrage and the power channel commenced in December 1995 and the Power Complex in February 1997. Going through the various stages of construction: impounding of the Barrage began on 17 February 2003, with filling of the power channel beginning on 9 April 2003, while the 500kV switchyard was energised on 30 April 2003.
Unit No.1 testing and commissioning began with the first mechanical run on 13 May 2003, and trial generation started on 16 June 2003, with generation of 50MW. 290 MW, the rated capacity of Unit No. 1, was fed into national grid starting 24 July 2003. All other units will come on line in three month intervals, and the completion of the entire project is scheduled for May 2004.
Related ArticlesMangla surveys scheduled for May
| Engineer |
| Pakistan Hydro Consultants – a joint venture of National Engineering Services Pakistan (Pvt) Ltd, Pakistan |
| Project Data |
| Barrage: Power Channel: Power Complex: |
| Test factfile |
| Para 1 Para 2 Line 1 |
