AN INTRODUCTION TO THE GENERATION OF ELECTRICITY IN PAKISTAN Electricity is the heartbeat of the modern world and is a measure of the progress of a country. Nowadays with the power generated you can turn deserts into gardens. Take Saudi Arab as an example, a country known for its barren deserts. It has now become able to export wheat just because of the electricity, with the help of which it is pumping water far into the deserts and is using electric sprinklers for spraying water on to the crop. Just look around yourself, our life depends a lot upon electricity. The lights, A.C.'s, T.V.'s, fans, computers and lots of other appliances are working just due to the invisible power of electricity. In short, nowadays life has become luminous just due to electricity. But the question is that "how this energy is generated?". According to the law of conservation of energy, we must give something to get something and from this law evolves the question, " What can we give to get Electricity? ". There are many ways to generate electricity, such as 1. Conversion of mechanical energy to electrical energy or electricity 2. Conversion of light energy to electricity 3. Conversion of chemical energy to electricity, etc. But the methods which are most to common to generate electricity are through the use of Nuclear, Hydel and Thermal energy by employing the method 1 written above. The choice of the electricity generation technique depends upon the cost per unit involved in the process. Here is a comparison of the cost per unit encountered in the generation of electricity through the above methods.
Transcript
AN INTRODUCTION TO THE GENERATION OF ELECTRICITY IN PAKISTAN
Electricity is the heartbeat of the modern world and is a measure of the progress of a country. Nowadays with the power generated you can turn deserts into gardens. Take Saudi Arab as an example, a country known for its barren deserts. It has now become able to export wheat just because of the electricity, with the help of which it is pumping water far into the deserts and is using electric sprinklers for spraying water on to the crop. Just look around yourself, our life depends a lot upon electricity. The lights, A.C.'s, T.V.'s, fans, computers and lots of other appliances are working just due to the invisible power of electricity. In short, nowadays life has become luminous just due to electricity.
But the question is that "how this energy is generated?". According to the law of conservation of energy, we must give something to get something and from this law evolves the question, " What can we give to get Electricity? ".
There are many ways to generate electricity, such as
1. Conversion of mechanical energy to electrical energy or electricity
2. Conversion of light energy to electricity
3. Conversion of chemical energy to electricity, etc.
But the methods which are most to common to generate electricity are through the use of Nuclear, Hydel and Thermal energy by employing the method 1 written above.
The choice of the electricity generation technique depends upon the cost per unit involved in the process. Here is a comparison of the cost per unit encountered in the generation of electricity through the above methods.
Thus it obvious that Hydel Power is one of the cheapest ways to produce electricity.
Here, the topic is the peak generation of1450MW of hydel power, through the Ghazi Barotha project, which is nearly half of what Tarbela Dam is producing right now.
A brief note about the present condition of the generation of electricity in Pakistan may be interesting at this stage. As in every other field, this country is suffering with a crisis in power generation also. Even in this developed age, 67 % of our population lives in darkness, without electricity. Due to a high population growth rate, the demand for the supply of electricity is also growing at the rate of 9 % annually. On the other hand, the supply is increasing a the rate of about 7 % and it is mostly due to the thermal power stations. Due to the dependence of electricity generation on these thermal power stations the cost of electricity is also rising rapidly. So, this country is in desperate need for a Hydel Power Station either in the form of Kala Bagh Dam or the " Ghazi Barotha " .
GHAZI BAROTHA HYDROPOWER PROJECT
The GHAZI_BAROTHA hydropower project is a major run-of-the river environmentally sustainable power poject, designed to meet the acute shortage of peak power demand in our country. The project os based on the utilization of the head available in the INDUS RIVER between TARBELA DAM near GHAZI confluence with the HARO RIVER and the INDUS river near BAROTHA. In this reach the INDUS RIVER drops by about 76m in a distance of 63km.
Layout of the Ghazi Bharota Project
The figure shows the detail of the project, it is evident that the project will have three main components :
Barrage Power Channel Power Complex.
The barrage located about 7km downstream of TARBELA DAM will regulate the daily disharges from Tarbela and divert the water into the power channel. The concrete lined power channel will convey upto 1600 cumecs ( 56,500 cusecs ) from the barrage to the power complex. The channel will be 52 km long. The power complex will be located near the confluence of the Indus & Haro Rivers. It has a peak capacity of 1450 MW using 5x290//mw turbo generators.
OPERATION :
The project will have an installed generating capacity of 1450 MW. The power will be available during the critical months of May and June when the whole country is short of power. The power channel is designed to require regular de-watering for maitenance and inspection. Other parts of the project can be isolated for maintenace during the low flow season.
COSTS :
The total capital cost of the project at the September 1993 price levels is estimated to be at US $2166 M including the transmission links to the national grid, physical contingencies, price contingencies and engineering.
One of the most important features of the project is that it provides power peaking capacity throughout the year with full power generation during the months if May and June when there is a reduced generation from other hydropower projects as a result of low reservoir levels.
FEASIBILITY REPORT :
The feasibility study of the project, completed in April 1997, demonstrated the technical, environmental and economic feasibility of the project. An independent panel of experts, established for the project has been invloved in the review of various technical aspects of the project from the beginnning of the studies and the panel has endorsed the project as technically sound and economically highly attractive.
PROJECT COMPLETION SHCEDULE :
ACTIVITY 1994 1995 1996 1997 1998 1999 2000 2001
LandAquisition ****** ****** Relocation and Resettlement Work
****** ****** ****** ******
Preparatory Work
****** ****** **
Barrage ****** ****** ****** ****** **
Power Channel ****** ****** ****** ****** **
Power Complex ** ****** ****** ****** ****** ******
The above table shows that the project will be completed in 2001. The preparatory work and the land aquisition has been nearly completed . The barrage, the power channel and the power complex will take about five years to be completed.
We hope that the project will be completed within time (INSHA-ALLAH) and will provide the power to the National Grid System round the clock.
TECHNICAL SITES
The Ghazi Barotha project has basically three different technical sites :
1. Barrage 2. Power Channel
3. Power complex
The whole project uses the fact that there is a difference of altitude between Ghazi and Barotha. This difference in altitude will be used to accelerate the water and this acceleration is utilized in producing power.
BARRAGE :
The barrage will be located at 7km from the Tarbela Dam. The following figure shows the basic construction.
Just before the village Ghazi the barrage pond woll be constructed. The functions of the barrage are :
To store the water,
To divert the water to the water channel.
There will be a seperating island on which the control house will be constructed. Near the right bank thee will
be 20 standard bays which will be used in regulating the water in the Indus. On the left bank there is a head regulator which will control the inflow into the channel. The good thing about the diversion is that the water required will be supplied through the year without any interruption. You can see a separating dyke which will be 1km long. The main purpose of the dyke is to save the village Ghazi from soil errosion.
POWER CHANNEL :
The diverted water from the barrage will go into the channel. The main purpose of the power channel is to carry water from Ghazi to Barotha with minimum losse in water. The dimensions of the channel are shown in the following figure.
It will be 9m deep and 58.4m wide. It will have on both sides 10m service road and 25
bridges will connect them. The spoil banks on either sides will be made from the soil extracted from the channel and will guard against some rise in water level. An interesting construction will be an under drainage which will stop under seeping of the water into the soil and thus saving valuable water. If by chance there is any seepage there will be another gravel layer which will not allow the water to enter the soil. Any water which seeps through the concrete lining will be collected in the sumps. Pumps will then carry this water back into the channel. Another benefit which will be derived from the channel is that water form any water logged area near the channel will enter it and hence reduce the water logging.
POWER COMPLEX :
The power complex is the most important part of the whole construction because Electricity will be produced here. The water from the power channel will enter the forebay. Any excess water in the rainy season will be stored in either the north head pond or the south head pond. The power house will have a pen stalk with 5 tunnels in them and in each tunnel there will be one turbine connected with a generator, having a capacity of 290MW. The speed of the water will be utilized to run the
turbines and in turn to produce power. This speed will be acheived from the negative gradient of the channel. A spillway is provided ot remove any undesired water any time. The water after utilization will re-enter the river Indus near Barotha.
PROJECT COST AND ECONIMICS.
Now you will get an over-view on the cost and economics of Ghazi Barotha Hydro Power Project. It will be completed by the year 2001. The total cost of the project is about 2.2 billion US dollars. Foreign exchange loan will constitute about 56 % of the total cost will the remaining 44 % will be provided by the Governement of Pakistan.
Let us see who the major contributors are apart from the Government of Pakistan :
Total foreign exchange loan : 250 Million US $
FINANCER AMOUNT, US $
( million )
%AGE OF
LOAN %AGE OF TOTAL
COST
World Bank 350 28 15.9
Japan 350 28 15.9
Asian Development
Bank 300 24 13.6
Germany 150 12 6.8
European Investment
Bank 60 4.8 2.7
Islamic Development
Bank 40 3.2 1.8
This table showas that the major financers are Japan and the World Bank. Each is providing 250 million US $ i.e., 28 % of the foreign exchange loan and 15.0 % of the total cost of the project.
Let us see what methodology and scales have been adopted to estimate the cost of the project.
1. The cost estimates are based on July 1990 price levels and at an exchange rate of Rs. 22 per US $.
2. Most prices were estimated by analytical methods, although few were based upon previous estimates or other past experiences, with appropriate adjustment.
3. The cost calculation were divided into local and foreign currency components. 4. Labour, cement, reinforcing steel, electricity, fuel and lubricants were considered
as local costs and the market prices for these items were used. 5. Equipment, spare parts, M & E palnt and equipment were considered as foregin
costs.
6. Tools, materials and supplies were considered to have a 25 % local and 75 % foreign currency comoponens.
7. Custom duties and taxes on imported equipment are not included in these estimates.
* Since, the exchange rate of US $ in Pakistani Rupee has risen considerably, as compared to the exchange rate discussed above, so the total cost has changed accordingly.
SUMMARY OF PROJECT COST BASED ON JULY 1990 PRICES WITH LOCAL CURRENCY ADJUSTED FOR INDIRECT FOREIGN COMPONENT. ( US $ 1.00 = Rs. 22 )
All three components require a lot of land for construction, so this section will explain the procedure and the process involoved in acquiring the land for the three. Out of the three, much land is required for the power channel as it is 52km long. Also, apart from the actual project the land is required for secondary purposes such as residential colonies, safety compounds, offices etc. Initial estimates have revealed that round about 5000 hectares of the land is required for the project.
PROJECT COMPONENT LAND REQUIRED
STATE OWNED PRIVATELY OWNED TOTAL
PERMANANT TEMPORARY
BARRAGE 1180 1180
POWER CHANNEL 133 867 1640 2640
POWER COMPLEX 950
950
TOTAL 1313 1817 1640 4770
The detailed account of the land required is presented in the table. We see that the land proposed for the barrage is about 1200 hectares of the state owned land. The power channel, which requires more than 2600 hectares of the land , is the lions share of the whole project. Only 133 of 1200 hectares is government owned and the rest is to be bought from the local people. The power complex to be built near BAROTHA requieres a thousand hectares of the land all of which is presently owned by the people.
These 5000 hectares lie in the two provinces NWFP and PUNJAB, most of it being in the NWFP. As far as the state owned land if concerned, we hope that there should be no problem in acquiring that unless some of the highest respected memebers of our society have their personal interests involved in the matter. We hope that by this time it must have been done. On the other hand, the aquisition of the land from rest of the people is really complex, as well as interesting.
When a group of GIK ( Ghulam Ishaq Khan Institute of Engg. & Tech. ) students went over to the site they had some really surprising experiences. When they talked to the them they were quite unsatisfied with the procedure adopted in buying the land. The procedure is as follows
A committee has been set up to evaluate the cost of the land consisting of the following members.
1. A representative from the local AC OFFICE, 2. A member from an NGO, 3. A local influential resident like a news reporter.
This committee decides the category of the land, such as commercial, residential, agricultural or barren etc. and then sets the rates per Kanal. Now these rates are the major problem in the setup. The rates vary from Rs. 1,98,000 to a mere Rs. 10,000 per Kanal. So, this difference has created a complex situation, in which sometimes the Patwari asks for a large bribe to transform your land from a category of lower worth to a higher one.
Although the process of land aquisition is more than 80% complete, but still, there are many complexities involved. Still many cases are in the courts waiting for a decision and long queues of people waiting for there decisions are common outside the AC office. Thus, the major problem is the huge difference in the rates of different categories. If one sees that he can get far more than what he is presently getting from his land then he tries his best to do it by using fair or unfair means. It is hoped that the Government along with the NGO's will try to satisfy people as much as possible, along with acquiring the land completely and as soon as possible.
EFFECTS OF GHAZI BAROTHA DAM PROJECT
EFFECT ON PEOPLE :
Seen as a whole, the project is undoubtedly a blessing for the people of Pakistan, as it will be a major step towards the solution of the prevalent energy crises. However, for the section of people belonging to the viccinity of the affected areas, the project is not less than a catastrophe. Twenty years ago they sacrificed their land and livelihood for TARBELA DAM PROJECT. They are again fore-seeing that they will have to give up the remaining land for the sake of their countries prosperity. Well, it's not too bad a deal!
The survey carried out by a team, comprising of the students of GIK ( Ghulam Ishaq Khan Institute of Engg. & Technology ), revealed that most of the people were not satisfied by the compensations which have been made by the government. They make the following complaints :
1. The power channel will act as a barrier for a farmer wishing to getting over the the other end of his peice of land, located on the other side of the channel. As a result, he will have to bear the additional burden of the bus-fare, evertime he goes from one part of his property to the other.
2. Diversion of water from Ghazi to Barotha will deplete the indus from Ghazi to Qazipur. This will have a drastic affect in the marine life and also, the lives of hundreds of tribesmen will be effected.
3. The attitude of the patwaris also poses a lot of trouble. They ask for hefty bribes, threaten them that if they fail to deliver the required sum they will declare their agricultural land as being barren and as a result the price of their land will drastically fall.
4. Preference is being given to the outsiders rather than the locals, regarding the availability of jobs, both technical as well as non-technical ones, at the construction sites. The job permits, which have been issued to them, have only proved to be a formality and the construction company has adopted a rigid and biased attitude towards the locals.
Some of these problems presented to these locals are no doubt genuine and they need to be addressed immediately. Though, some of the NGO's are apparently striving to look after the greviances of the local people, yet, their has been no visible improvement in the situaiton.
EFFECT ON THE ENVIORNMENT :
The project is not expected to induce a major influence on the enviornment. Such effects on the enviornment are predicted on the basis of experience with a similar project in a comparable enviornment. Direct or primary effects can usually be fore-seen and from them the indirect effects can be concluded.
EFFECT OF THE BARRAGE :
The most significant effect will be on the aquatic enviornment and the conversion of a stretch of braided river bed into a fluctuating pool, with a maximum area of 1,000 hectares. The present land used for the river bed is a source of cobbles and fuel wood with some land used for grazing and for fishermans' camps. As a result of the construction of the Barrage, the price of land will increase as it shifts from agricultural to commercial development.
EFFECT OF THE POWER CHANNEL :
About 1000 hectares of land will be taken by the power channel and its right-of-way including an allowance for the contingencies. After rehabilitation it will become a much impoved area.
The major land aquisition near Barotha will be about 850 hectares. About 40 % of this land is arable, of which only 6 % is irrigated. The rest currently is woodland, pastureland and wasteland.
EFFECT ON THE RIVER INDUS :
The ground water inflow-outflow relationship along the river will be somewhat altered. The presence of pond upstream of Ghazi will increase recharge from the river locally, now limited to the periods of high flow. From Ghazi to Qazipur, the period of recharge will be somewhat shortened and the dry season outflow to the river will be somewhat increased. This will not affect the locals, as at the present, only a small percentage of the consumptive requirements of the 15 riverside villages is met from the river; the rest comes from the ground water.
The feasibility report says that the reduction of flow in the river is not expected to effect the local livestock as substantial pools woll still remain. This contradicts to what the local people claim that not only will there be no aquatic life left, but also water for drinking purposes will be adversly affected. The government sources, however, claim that 80 % of the villages have sufficient ground water beyond their domestic requirements and hence this reduction in flow will not effect the villages that badly.
ENVIRONMENTAL EFFECT MITIGATED
RELEASE OF COMPENSATION WATER ADOPTION OF MARKET VALUES OF LAND
RESETTLEMENT OF HOUSING UNITS ON REPLACEMENT COST
COMPENSATION FOR LOSS OF CROPS, TREES ETC.
REPLACEMENT OF THE INFRASTRUCTURE.
THE CONCLUSION
With plans afoot to bring electricity to every village in the country, coupled with the need for greater industrial growth to cater for the enormous requirements of Central Asia, the per capita energy utilization in Pakistan is set to grow.
However, in spite of their protestations to the contrary the WAPDA authorities have initiated countrywide load shedding in the past. The perspective of the situation was that many of the medium and small scale industrial units were lying idle and many of the larger units have been running at less than full capacity !!
The writing on the wall is too clear and far too far from being comfortable. The demand supply gap in our electrical power generation is negative and with the progress of time, day by day, month by month and year by year, this gap is projected to widen, not arithmetically, but close to exponentially! However we can somehow avoid worse conditions if we start acting promptly from the time on.
Indeed, the requirement for power generation in Pakistan is becoming more and more crucial. It is important not only for our technical and socio-economic growth, but has also become imperative to sustain the present state of affairs.
Of the a major forms of power generation, there are three options available to us i.e., Nuclear, Thermal and Hydel.
Nuclear, though expensive as far as the infra structural requirements are concerned, will definitely be the most economical one to generate power for a longer time span and with a proper and diligently maintained safe-guards against radiation leaks it will have comparatively no short term effects on the environment. However, due to a number of external political factors our capacity to depend on it, alone for power-generation, is somewhat restricted.
Thermal energy generation is dependent on fossil fuels, which have to be imported as their availability in the country is somewhat restricted. Also, it is a fact their extraction is costly process, which has a direct impact on the cost of the generation of electricity.
Cost per unit of electricity is a major consideration in Pakistan. Why is the emphasis being laid so much on the cost ? It's because, being a third world nation and having a weak economy, the cost must be of major concern for any such Government which wishes to remain in power.
Envioronmentally, the thermal power genration is a distaster. It is a direct form of power generaion devised by man. Whether the power stations are run on fuel-oils, gas or coal, the end products , i.e., the burnt hydrocarbons and the organic materials, are bing perpetually released into the atmosphere. In contrast, the number of adverse environmental damages caused by Nuclear or Hydel generation systems are negligible.
The most non-controversial mode of power generation in Pakistan shall always by the Hydel mode of Power Generation. As discussed before, this project might have its own socio-economic effects, but years of research and feasibility reports by world class experts have cleared up the confusion in the air to such a large extent that the project may by be regarded as a model in itself.
Once it starts working, it will provide the nation with a continuous peak power of 1250KW. 24 hours a day, 365 days a year and year after year, as long as the Indus continues to flow past its huge turbines, a continuous supply of power will be guaranteed. After its passage through the dam, the water will still by clean, deep blue and environmentally friendly. Perhaps, it may by slightly magnetically charged due the effect of the generators, but it is a fact that magnetic water is health friendly.
By and large the Ghazi Barotha Power Project has overcome the minor discrepancies and irritants, which in any case form an integral part of all projects of this type. It is well on its way to completion by the beginning of the next century.
Water flows from the power channel into the forebay and is stored in two adjacent headponds with a combined capacity of 25.5 million m3 Around 100km from Islamabad on the Indus River this 1450MW hydropower project has provided an unprecedented opportunity for Pakistan’s economy, through enhancing power capacity, reducing dependence on limited fuel imports into the country and cutting greenhouse gas emissions.
Benchmark for best practice
Work on the Ghazi-Barotha hydropower project has received prestigious acclaim, highlighted by its success in winning the Energy Institute’s International Platinum Award 2006. It is destined to provide an example for future projects in Pakistan and beyond, not least for its focus on the social and economic needs of village communities. Mott MacDonald, in consortium, provided comprehensive site supervision services for the project, which is recognised for its role in establishing many industry good practice standards.
From the outset, the national utility Water and Power Development Authority (WAPDA) placed great emphasis on the rural community and held consultative meetings with representatives from key stakeholder groups in order to address environmental and social effects. Because the power channel location was carefully chosen to run through the foothills avoiding villages, only 110 families had to be relocated. These families received funds to build new houses in three specially developed villages.
Waste improvisation
Pakistan has more than 600km of link canals that convey irrigation water from one river to another and in most cases the excavation material arising from their construction was dumped on the banks creating waste lands. For the first time in Pakistan, material excavated on this project has been used to create spoil banks topped with cultivatable soil to act as farmland. WAPDA also plans to provide tubewells where sub-soil water is available for irrigation. In total, 158 such banks were created, with a total area of about 809ha.
Innovative thinking
Another innovative approach enabled the size of the power channel to be kept to a minimum. Water flows from the channel into the forebay and is stored in two adjacent headponds with a combined capacity of 25.5 million m3. The ponds augment the 1600 cumecs of discharge from the channel to 2200 cumecs, thereby providing enough water to operate the power plant (five 290MW turbine generators) at its full capacity every day throughout the peak demand period.
A further innovation is the forebay itself, which contains a self-priming siphon spillway that features no moving parts. Its function is to spill excess water while maintaining the ideal operating level for maximum hydraulic power. This design allows a low weir flow to spill above the normal operating level until the maximum normal level of the forebay and ponds is reached. At this point it primes fully and the spillway flow increases to its maximum.
A fibre optic link cable between the power complex and the barrage at the head of the channel means it’s possible to monitor water control and other features of the project at all times. The scheme has a distributed control system which enables the power station to be remote controlled from start up to shutdown and provides full diagnostic capability, ensuring that faults are traced in the shortest possible time.
Result
Indigenous oil, gas or fossil fuels in Pakistan are limited and so expansion in generating energy capacity relies on hydropower to reduce fuel imports – a need well fulfilled by this $2.25 billion run-of-river scheme. Ultimately, the Ghazi-Barotha Hydropower Project represents an extraordinary combination of collaboration, fresh thinking to provide cost benefits to the contractors and innovative solutions to bring benefits to its management and the surrounding community.
Tarbela Dam
Tarbela Dam is one of the world’s largest earth and rock filled Dam and greatest water resources development project which was completed in 1976 as a component part of Indus Basin Project. The Dam is built on one of the World’s largest rivers – the Indus known as the “Abbasin” or the father of rivers.
Emerging from the land of glaciers on the northern slopes of Kailash ranges, some 17,000 feet (5182 meters) above sea level, the river Indus has its source near the Lake Mansrowar in the Himalyan catchment area. It flows over 1800 miles (2900 k. metres) before it outfalls into the Arabian sea draining an area of about 372,000 square miles (964,261 sq.kms).
The World Bank accepted Tarbela Dam Project as a part of the Settlement (Replacement) Plan under Indus water treaty in 1965. WAPDA was entrusted with its execution on behalf of the Government of Pakistan. HARZA ENGINEERING COMPANY International who were the General Consultants of WAPDA, carried out the review studies of the Project. In February, 1960 Tippetts – Abbett - McCarthy – Stratton of USA commonly known as TAMS were appointed the Project Consultants, and were entrusted with the task of investigation, preparation of detailed designs, and contract documents for the project and also the supervision of construction work during its execution.
The Project – Main Features
The Project consists of a 9,000 (2,743 meters) long, 465 feet (143 meters) high (above the river bed) earth and rock fill embankment across the entire width of the
river with two spillways cutting through the left bank discharging into a side valley. Its main spillway has a discharge capacity of 650,000 cusecs (18,406 cumecs) and auxiliary spillway 850,000 cusecs (24,070 cusecs). Two auxiliary embankment dams close the gaps in the left bank valley. A group of 4 tunnels (each half a mile long), through the right abutment rock have been constructed for irrigation releases and power generation. During the construction operations, these tunnels were used initially for river diversion. Irrigation tunnel 5 situated on the left bank, for which NESPAK were the Project Consultants, was put into operation in April 1976.
A power station on the right bank near the toe of the main dam houses fourteen(14), power units, 4 units, each with installed generating capacity of 175 MW are installed on tunnel 1, 6 units (NO.5 to 10), 175 MW each on tunnel NO.2 and 4 Units ( NO.11-14) of 432 MW each on Tunnel 3, thus making total generating capacity of Tarbela Power Station as 3478 MW.
The reservoir is 50 miles (80.5 km) long 100 square, miles (260 square kilometers) in area and has a gross storage capacity of 11.6 MAF (17.109 million cu. Meters) with a live storage capacity of 9.7 MAF (14,307 million cu. Meters). The total catchment area above Tarbela is spread over 65,000 sq. miles (168,000 sq. kilometers) which largely brings in snowmelt supplied in addition to some monsoon rains. Two main upstream tributaries join the Indus river, Shyok river at an elevation of 8,000 ft. (2438 meters) above seal level near skardu and Siran river just north of Tarbela.
Main Dam
The principal element of the project is an embankment 9,000 feet (2743 meters) long with a maximum height of 465 feet (143 meters). The total volume of earth and rock used for the project is approximately 200 million cubic yards (152.8 million cu. Meters) which makes it the largest man made structure in the world , except for the Great Chinese Wall which consumed somewhat more material. The main embankment is a carefully designed, zoned structure composed of impervious core, bounded on both sides by gradually increasing sized material including coarser sands gravels cobbles and finally large sized riprap on the outer slopes. An impervious blanket, 42 feet (12.8 meters) thick at the dam and tailing to 5 feet (1.52 meters) at the upstream end, covers 5,700 feet (1737 meters) of the alluvial foundation on the upstream side. These deposits in the valley are upto 700 feet (213 meters) deep and in places consist of open work gravels. The dam crosses this essentially alluvial valley and connects the last points to high ground before the mountains give way to the plains. A 24 feet (7.32 meters) thick filter drain mattress under the embankment together with nearly vertical chimney drain provides the necessary facility to collect the seepage.
Auxiliary Dams
The auxiliary dams resembling the main embankment dam in design close the gaps in the left periphery of reservoir. The smaller of the two auxiliary dams, however, has a vertical core extending down to the underlying rock, and the larger auxiliary dam has a short upstream blanket terminating in a cut off to rock.
Spillways
On the left bank , two spillways discharges into a side channel. The total spillway capacity is 1,500,000 cusecs (42,476 cumecs) which constitutes the peak outflow resulting from routing the probable maximum flood. The service spillway having 44 percent of the total capacity is sufficient to pass all but very rare floods. Its maximum discharge capacity is 650,000 cusecs (18, 406 cumecs).
The auxiliary spillway is similar in design to the service spillway. It has nine radial gates with crest elevation of 1492 feet (455 meters) and flip bucket at elevation 1220 feet (372 meters) A longitudinal drainage gallery along with a network of drainage pipes under the channel and the head works has been provided to release pore water pressure in both the spillway foundations.
Reservoir
The 50-miles (81 kilometers) long reservoir created by the Project has a gross storage capacity of 11.6 million acre feet (MAF) (17,109 m.cu. meters) at the maximum lake elevation of 1550 feet (472 meters) a residual capacity of 1.9 MAF (2,802 m cu. Meters) at the assumed level of maximum drawdown elevation 1300 feet (396 meters) and a net usable capacity of 9.7 MAF (14,307 m cu. Meters). The Tarbela reservoir stores water during the summer months of June, July and August when water either causes disaster by flooding in the surrounding areas or goes waste into the sea. It is to be noted that more dams can be constructed on Indus since its annual flow is substantially more than is being stored at present. Kalabagh Dam on River Indus is in its advanced stages of design, while investigations are underway for the upstream Basha Dam.
Tunnels
The four, each of half mile long, tunnels through the right (rock) abutment initially served for the diversion of water during the final phases of construction of the Project. Now they are being used for Power generation (tunnels 1, 2, 3 and eventually 4). The discharge capacity of each irrigation tunnel at higher reservoir elevations is approximately 90,000 cusecs (2,549 cumecs). The discharge pass through energy dissipator structures and the water returns to the river. A fifth tunnel on the left bank designed to augment irrigation releases upto 80,000 cusecs (2,265 cumecs) at high reservoir level, has also been added to the project.
Power Station
According to the original plan, four (4) power units of 175 MW generating capacity each were to be installed on each of the tunnels 1, 2 and 3 located on the right bank with the ultimate installed capacity of 21,00 MW. Of these, four (4) units on tunnel 1 were commissioned in the year 1977. Due to increasing prices of the fossil fuel, the Govt of Pakistan has been laying greater emphasis on generation of cheap Hydel power. In pursuance of this policy, WAPDA carried out studies to tap the maximum power potential of Tarbela. As a result, it has been found possible to install six (6) units, instead of four (4) only on tunnel NO.2. Units 5 to 8 on tunnel NO.2 were commissioned in 1982, and units 9 and 10 in 1985. Based on studies, four power units of 432 MW capacity each were installed on tunnel NO.3. Thus the total ultimate power potential of the project enhanced from 2100 MW as originally planned to 3478
MW.
Project Implementation
On May 14, 1968, the World’s largest single contract for the construction of civil works of the Tarbela Dam Project was signed at a price of RS.2,965,493,217 ($ 623 Million) between the Water and Power Development Authority and the Tarbela Dam Joint Venture which comprised a group of three Italian and three French heavy construction contractors. Later five German and two Swiss contractors also joined the group making up a consortium of thirteen European firms led by Italian firm namely Impregilo.
The construction of Tarbela Dam was carried out in three stages to meet the diversion requirements of the river. In stage-I, the river Indus was allowed to flow in its natural channel while work was continued on right bank where a 1500 feet (457 meters) long and 694 feet (212 meters) wide diversion channel was excavated and a 105 feet (32 meters) high buttress dam was constructed with its top elevation at 1, 187 feet (362 meters) The diversion channel was capable of discharging 750,000 cusecs (21,238 cumecs). Construction under stage-I lasted 2½ years.
In stage-II, the main embankment dam and the upstream blanket were constructed across the main valley of the river Indus while water remained diverted through the diversion channel. By the end of stage-II, tunnels, had been built for diversion purposes. The stage-II construction took 3 years to complete. Under stage-III, the work was 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 a part of stage-III works.
