Engineering the Three Gorges Dam
Building the World's Largest Hydroelectric Power Plant
Sep 22, 2009
When the Three Gorges Dam in China's Hubei province is fully operational in 2011, it will have a power generation capacity of 22.5 GW.
The Three Gorges Dam and its hydroelectric power plant will provide electricity to a wide swath of central China along the Yangtze River all the way to Shanghai on the eastern coast. This massive undertaking required significant planning and management to overcome the immense engineering challenges presented by such a venture.
What is the Three Gorges Dam?
The Three Gorges Dam is a hydroelectric dam and power plant on the Yangtze River within Hubei province in central China. Construction on the facility began in 1994, and the main dam structure was completed in 2006.
The facility began generating electricity in 2003, and the hydroelectric plant will reach it's full capacity in 2011. The dam structure is a concrete gravity dam design with a wall height of 101 m (331 ft) high. The wall is 115 m (377.3 ft) thick at its base, tapering to 40 m (131.2 ft) at the top.
Balancing Dam Functions
Although the Three Gorges project is primarily associated with it's hydroelectric power plant, of equal, or perhaps greater importance is the dam's function as a flood control system for the Yangtze River. The Yangtze River floods regularly, and has caused catastrophic loss of life and property throughout history. Several large cities, including Shanghai are situated on its banks, and are at risk of flood damage during the rainy seasons, according to the Xinhua news agency.
Reservoirs created for flood control generally maintain a low reservoir level as compared to the overall dam height in order to capture and retain flood waters when they occur. However, reservoirs created for hydroelectric power generation are designed to have as high a reservoir level as possible to maximize the amount of head potential of the water.
These two functions are balanced by raising and lowering the reservoir height at specific points during the year. The reservoir is reduced during the winter dry season to leave space for the rainy season later in the year. By increasing the water flow during the dry season, the dam also assists farmers downstream by providing additional water when there is no rain.
Improving Shipping Lanes
The Yangtze River in the Three Gorges area was not an easily navigable waterway prior to the construction of the dam. The flooding of Three Gorges dramatically improved navigation along the river, but the dam design needed to allow ships to pass in order to maintain, if not expand water shipping.
The Three Gorges Dam includes two sets of locks, each with five cells, allowing for ships to move in either direction through the locks. The dam also has a ship lift under construction. The ship lift design has been modified several times, and as of 2009 has not been completed. The current design calls for a capacity of 3000 tons. Ships using the lift can cross the dam in about 40 minutes, as opposed to 3-4 hours for the lock system, according to the BBC.
In addition to these challenges, the engineers and construction crews have to account for a dynamic landscape. The Three Gorges Dam lies over a fault line, so the dam structure has to be able to withstand forces from earthquakes. Also, landslides can displace significant amounts of water, leading to the potential for mini-tsunamis. The Three Gorges Dam is certainly a model of engineering and construction expertise, rivaled in China only by the Great Wall.
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