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
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
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.
Copyright
2011 Lee Krystek. All Rights Reserved.
