Megadam: The Itaipu

The main dam at Itaipu with its powerhouse. (Photo by Cyc. Licensed under Creative Commons ShareAlike 1.0 License.)

In the 1960’s the governments of Brazil and Paraguay saw a way of working together on a project that used one of their shared resources to support the expanding electrical needs of their countries. This resource was the Paraná River, the seventh largest in the world, which formed a natural border between the two nations. The project was a massive dam that would harness the river’s energy and turn it into electrical power.

On July 22, 1966, the Brazilian and Paraguayan Ministers of Foreign Affairs signed a document agreeing to explore the possibility of building a dam and an associated hydroelectric plant. It wasn’t until February 1971, however, that the work actually started. Once construction was underway, there were still legal considerations to be handled. In particular, the country of Argentina, only a few miles south of the dam site, was concerned that in times of conflict the dam could be used as a weapon. If all the gates were opened, a rush of water could be created that would flood the Argentine capital of Buenos Aires. To quell these concerns the three nations entered an agreement in October of 1979 on the amount of water that could be released at any time from the dam.

Seven Quick Facts
Height: 738 feet (225m)
Length: 4.8 miles (7.2km)
Finished: May 5, 1984
Cost: $18 billon
Location: Paraná River between Brazil and Paraguay
Made of: Concrete and steel on the main dam, with earth and rock on side dams.
Other: In 2008 generated 94,684 megawatts, the largest amount of power ever produced by a single dam

During the planning stages the engineers had to decide what type of dam was needed and how big it should be. A simple dam placed at the chosen spot on the river would have blocked it, but only would have created a lake 150 feet deep, not enough to produce all the power that was wanted. Instead, it was decided to make the Itaipu not just a single dam, but a series of dams 4.8 miles (7.2km) long and 738 feet (225m) high. This would permit the creation of an immense lake that would allow the Itaipu to produce more hydroelectricity than any other dam in the world.

The four dams would consist of an earthfill dam, a rockfill dam, a main dam built with concrete and also a concrete wing dam. All the dams would hold back the water based on their huge size and sheer weight (what is referred to as a gravity dam). Gravity dams are different from structures like the Glen Canyon Dam in the United States. The Glen Canyon Dam is a thin concrete arch that holds back the water by pushing against the sides of a narrow canyon. Instead the Itaipu dam would have a cross section that looked like a huge triangle, wide at the base where the water pressure would be greatest and narrow at the top.

Diverting the River

One of the massive generators at Itaipu that can produce over 700 megawatts. (Photo by Anagoria. Licensed under Creative Commons Attribution 3.0 Unported license.)

The first job the construction crew had to do was to divert the flow of the river around the construction site so that it was dry enough to start buiding. As the Paraná is one of the largest rivers in the world, this project in itself was a challenge. Over 50 million tons of rock and earth were removed to create a bypass channel for water that was 490 feet wide, 300 feet deep and 1.3 miles long. In addition, temporary cofferdams were placed in the river’s old path to keep water out of the construction zone. This river diversion was the largest ever attempted and took three years to complete. On October, 1978, the new channel was opened by blasting the concrete blocks out of the way and letting the water pour through.

The construction of the dam itself required 40,000 workers, mostly recruited from Brazil. To house them, a whole new community was built including hospitals, schools, parks and churches. Unfortunately, 149 of these employees were killed during the construction project.

More than 12.3 million cubic meters of concrete were poured to create the dam. Some sections of concrete were so large that if allowed to set naturally in the hot sun they would not have dried properly, causing cracks and weak spots. To avoid this, large-scale refrigeration plants (equivalent to 50,000 domestic deep freezers) were used to cool the concrete while it hardened.

In addition, enough iron and steel were used during the construction to build 380 copies of the Eiffel Tower. More than 8.5 times the rock and soil were moved in the building of the dam than was needed to cut the channel tunnel between England and France. The construction also used 15 times more concrete than the “Chunnel.”

Filling the Reservoir

The layout of the Itaipu Dam site.

On October 13, 1982, the dam was completed to the point where the diversion channel could be closed and the lake filled. Because of heavy rains during this period, it took only 14 days to fill the reservoir which was 105 miles (170km) long and 4 ½ miles (7km) wide. When the lake was filled it contained 29 billion tons of water.

On May 5, 1984, the first of the power-generating units was completed and brought on-line to officially open the dam. The rest of the units would be installed over the next seven years, slowly increasing the capacity of the dam each year.

The main concrete dam at Itaipu is where the hydroelectric plant, that produces the power, is located. Construction crews installed twenty giant turbines into the half-mile-long power house. Each turbine was 53 feet across and weighed 800 tons. The turbines were connected to twenty generators that could each produce 700 megawatts of power. When they were all installed this gave the dam a theoretical generating capacity of 14,000 megawatts. However, only 18 of the turbines are used at one time to keep the water flow under the limits determined by treaty with Argentina. The extra units, though, allow two of the turbine/generators to be off-line for maintenance while the rest continue operating.

In 2008 the dam generated 94,684 megawatts, the largest amount of power ever produced by a single dam. This electricity supplies Paraguay with almost 90 percent of its power and Brazil with around 25 percent. The dam, a renewable energy source, produces the equivalent amount of power as burning 434,000 barrels of oil per day.

The Environmental Cost

These huge pipes feed the water into the giant turbines to make electricity (Photo by Wutzofant. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported)

While the Itaipu Dam is an amazing achievement and was selected by the American Society of Civil Engineers as one of the Seven Wonders of the Modern World, its construction did come at a cost. Almost 10,000 families had to be relocated before their homes were flooded by the growing reservoir. Also, the spectacular Guaíra Falls was submerged under the lake and then dynamited to allow safe navigation of the river. The Guaíra Falls, also known as the “Seven Falls,” was thought by many to be the most spectacular natural water feature in the world. It had a total height more than twice that of Niagara Falls and a water flow that was more than double. The Brazilian poet Carlos Drummond de Andrade wrote:

Here seven visions, seven liquid sculptures vanished through the computerized calculations of a country ceasing to be human in order to become a chilly corporation, nothing more. A movement becomes a dam. -Carlos Drummond de Andrade, “Farewell to Seven Falls”

Sometimes progress is a mixed blessing.