The Itaipu Dam is a bi-national hydro-electric power generation station located on the Paraná River in South America, which is operated jointly by the states of Brazil and Paraguay. It is a critical electricity generation station for supplying Brazil, the seventh-largest economy in the world, with nearly one fifth of its energy needs.
The key environmental benefit of Itaipu Dam is the supply of electricity through the harnessing of water power without the need for burning coal or oil, as required in fossil-fuel power stations.
The Itaipu Dam is the largest hydro-electric power station in the world in power output terms, at 98 trillion watt-hours generated per annum. This is in spite of the fact that Itaipu Dam is only the second-largest station in generation capacity terms at 14,000 megawatts, after the Three Gorges Dam in China, which has a 22,000 megawatt capacity, generating a lesser 85 trillion watt-hours per annum.
The Itaipu Dam maintains its power generation position due to the climatic conditions of the region. The consistent rainfall of 2,500 millimetres per month ensures stable water reservoir levels, thus enabling year-round power generation from the dam.
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Inside the concrete 'hollow gravity' structure of Itaipu Dam[/caption]
The states of Brazil and Parguay signed the Itaipu Treaty in 1973 for development of the project, which coincided with the Middle East Oil Crisis – thus creating the momentum for developing non-fossil fuel, renewable-energy projects in Latin America.
The construction of the Itaipu Dam started in 1974 and it was commissioned in stages over 30 years, with all 20 electricity generators operational by 2007. The dam was designed by the Indian engineer Gomurka Sarkaria as a ‘hollow gravity’ type of dam, consisting of multiple concrete diamond-shaped structures which are 195m in height.
The main concrete dam and outer embankment dams are over 7km in length. The lateral hydraulic loads from the reservoir water are transmitted through the ‘v-shaped’ structures into the basalt rock foundations thus ensuring the structural stability of the main dam. The adoption of the hollow-gravity dam led to a 30% reduction in the volume of concrete required to construct Itaipu and reduced overall construction costs by 12%.
First stage of construction
The first stage of construction involved the temporary diversion of the Paraná River to enable construction of the main dam. The diversion was 2km in length and involved the excavation of 55 million cubic metres of material.
The temporary diversion of the river required construction of a ‘diversion dam’ to control the outfall of the diverted Paraná River. With the river diversion in place, the construction of the main hollow-gravity dam commenced. An onsite concrete plant at Itaipu supplied the concrete for construction of the main dam, which was equivalent to pouring concrete for a 22-storey building every hour, 24 hours a day.
A key quality-control issue during construction was temperature variation during concrete curing. The solution was the addition of ice flakes to the concrete to maintain a temperature of 7 degrees centigrade. This prevented bubble formation within the concrete due to over-heating, which reduced the possibility of crack formation in the concrete dam structure. The total volume of concrete required for construction was 12.3 million cubic metres.
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The chamber room for access to the turbine generators located in the floor[/caption]
The main dam structure also consists of a large concrete spillway for reservoir level control and an outer rockfill dam embankment to surround the reservoir. The rockfill dam embankment is constructed from basalt rock, compacted soil and filter material, which prevents water penetration from the reservoir to ensure embankment stability.
Upon construction of the main dam and the rockfill embankment, the Paraná River basin was flooded to create the reservoir over an area of 1350 square kilometres, which extended 170km upstream from the dam and had an average width of 9km.
The creation of the reservoir facilitated water supply for the 10 metre diameter Penstock pipes connected to the turbine generators within the dam. The reservoir has a depth of 118m behind the dam face with an average depth of 22m.
How Itaipu Dam generates electricity
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The 10m-diametre Penstock pipes in Itaipu Dam[/caption]
For generation of electricity, the dam consists of 20 hydro-electric generators with 16 generators located in the main dam and four of these located within the diversion dam, originally constructed for the river diversion. The first generators started electricity generation in 1984 with 18 operational by 1991 and the maximum of 20 generators operational by 2007.
Each Penstock pipe facilitates a flow of 7000 litres of water per second, thus creating the rotary movement of the turbine generator blades which enables electricity generation based on the rotation of the each generator’s magnetic plates.
Each generator has a capacity of 700 MegaWatts. The turbine generators weight 3700 tonnes each and are accessed from a Chamber Room within the dam which is nearly 1km in length. The turbine generators are removed for maintenance by overhead cranes within the Chamber Room. The majority of the generators were supplied by the German engineering company Siemens.
The electricity from the turbine generators is then increased in voltage through electrical transformers from 18 Kilovolts to 500 Kilovolts to facilitate transmission to both Brazil and Paraguay. The Itaipu Dam supplies 90% of its electricity output to Brazil, supplying 17% of Brazil’s energy needs with the remaining 10% of output supplying 75% of Paraguay’s energy requirements.
The operational system for control of the Itaipu Dam is the digital SCADA (Supervisory Control and Data Acquisition) control system which informs the station engineers about the electricity output of the generators and the reservoir levels to ensure safe management of the power station.
The digital SCADA system replaced the older analog dial-reading system in 2002. However, the analog system is still relied upon as an emergency back-up system in the event of a failure of the SCADA system.
Environmental impact of Itaipu Dam
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Biodiversity Corridor at Itaipu Dam connects the original animal reserves to the larger Iguazu National Park[/caption]
The environmental impact arising from construction of the Itaipu Dam was not without controversy, particularly in relation to the creation of the reservoir. The creation of the reservoir displaced 40,000 local inhabitants who were relocated to adjacent rural lands or provided with monetary compensation.
The impact on wildlife habitats led to the creation of eight adjacent animal reserves to which the various animal species were relocated by zoological experts. In 2003, a Biodiversity Corridor was created in parallel with a re-forestation programme, which linked the original animal reserve areas to the larger Iguazu National Park – thus ensuring a survival rate of 70% for newborn animals in the area.
A fish pass was constructed as part of the environmental mitigation measures to enable aquatic life to pass from the downstream Paraná River to the upper reservoir area behind the dam. This measure was unsuccessful, however, and a revised fish pass was constructed in 2002 to address this issue. The revised fish pass consists of 6km of concrete channel and 4km of natural channel over a rise of 100m to enable fish passage up the Paraná River.
This revised type of fish pass is now mandatory for new hydroelectric dams, which are needed to meet Brazil’s energy requirements for its 200 million people. The Seven Falls waterfall on the upstream section of the Paraná River was also submerged with the creation of the reservoir. This illustrates the trade-off the engineers had to consider as part of project planning, between electricity supply needs for development and environmental impacts.
The bi-national partnership which operates Itaipu Dam recently received a number of environmental protection awards including the Earth Charter Award for water quality protection, which indicates its commitment to best practice in this area.
The total cost of the dam was US$16 billion, which was financed by government and private commercial loans. The loans for the Itaipu Dam will be fully repaid by 2023. In terms of ensuring the supply of engineers and scientists to maintain the dam in the future, a new university will be opened beside the dam in 2017 with a capacity for 10,000 students from both Brazil and Paraguay.
These students will build on the legacy of the engineers and managers who designed and built the Itaipu Dam. Their engineering experience and knowledge was of international renown and was used to mentor the Chinese engineers who went on to design and build the Three Gorges Dam in China.
Summary
Over the past decades, the Itaipu Dam has served a key role in supplying clean energy for the states of Brazil and Paraguay. Lessons have been learned during the construction and operational stages of the project which can guide the planning of new hydro-electric power stations in Latin America, in terms of balancing national energy needs with environmental protection.
The Itaipu Dam project is an illustrative model of how the emerging states can work together to harness nature’s power for sustainable development in the coming decades.
Author: Paul MacDonald BSc (Eng) BSc (Politics) MIEI is a highway engineer/training officer with Kildare National Roads Office. He has 20 years’ experience in highways, water and environmental engineering. He is a divisional representative on the Council of Engineers Ireland and is involved in the Engineers Ireland STEPS school liaison programme. MacDonald has a keen interest in topics such as urbanisation in the emerging states, international engineering contracts and project finance.