2008

Three Gorges Dam

Why do engineers build dams? Dams tend to be huge and expensive, so there must be a good reason. One of the best reasons is flood control. A wild river can be a powerful destructive force for the people who live nearby. A wet season can turn a peaceful river into a raging, flooding torrent. Or, if neighboring land is flat, floodwater can spread out over many square miles. The lake behind a dam can instead store the flood and release it at a reasonable rate, or save it for things like irrigation later in the year, as in India.

Another reason is drinking water. A big dam with a big lake behind it can provide a reliable supply of drinking water for millions of people. This is one of the major benefits of the Hoover Dam.

Another reason is hydroelectric power. A dam across a large river can create large amounts of electricity, like the Itaipu Dam.

Then there is navigation. A big part of the Panama Canal is not a canal at all, but is instead a route across a giant manmade lake.

What if engineers are able to achieve all of these goals with one dam? That is what the Three Gorges Dam in China, initially surveyed by American civil engineer John L. Savage in 1944, has been able to accomplish. Original plans for the dam began in 1932 under Chiang Kai-Shek’s Nationalist government, but construction did not start until 1994.

The Three Gorges Dam is immense—7,660 feet (2,335 meters) long and 594 feet (181 meters) tall. It houses thirty-two 700-megawatt generators, giving it by far the largest electrical generating capacity in the world. By generating an expected 100 billion kilowatt-hours of electricity per year, the dam should be able to pay for itself in just 10 years.

The lake behind the dam is over 400 miles (600 km) long and holds 40 cubic kilometers (10 cubic miles) of water. To put that in perspective, if one billion people used 10 gallons of water from the lake every day for a year, it would only use one third of the water behind this dam.

SEE ALSO Hoover Dam (1936), Green Revolution (1961), Itaipu Dam (1984).

The Three Gorges Dam in China is the world’s largest power station.