Three Gorges Dam , in China



Three Gorges Dam dam, China

Three Gorges Damdam on the Yangtze River (Chang Jiang) just west of the city of Yichang in Hubei provinceChina. When construction of the dam officially began in 1994, it was the largest engineering project in China. At the time of its completion in 2006, it was the largest dam structure in the world. The dam and accompanying hydroelectric plant were built in phases and over the course of many years. It reached its full generating capacity in 2012. The dam allows the navigation of oceangoing freighters and generates hydroelectric power. It was also intended to provide protection from floods, but efficacy on this point is unclear and has been debated.

While the construction of the Three Gorges Dam was an engineering feat, it has also been fraught with controversy: construction of the dam caused the displacement of at least 1.3 million people and the destruction of natural features and countless rare architectural and archaeological sites. The dam’s reservoir is blamed for an increase in the number of landslides and earthquakes in the region.

Physical description and capacity of the Three Gorges Dam

A straight-crested concrete gravity structure, the Three Gorges Dam is 2,335 metres (7,660 feet) long with a maximum height of 185 metres (607 feet). It incorporates 28 million cubic metres (37 million cubic yards) of concrete and 463,000 metric tons of steel into its design. Submerging large areas of the Qutang, Wu, and Xiling gorges for some 600 km (375 miles) upstream, the dam has created an immense deepwater reservoir allowing oceangoing freighters to navigate 2,250 km (1,400 miles) inland from Shanghai on the East China Sea to the inland city of Chongqing. Navigation of the dam and reservoir is facilitated by the five-tier ship locks at both ends of the complex, which allow vessels of up to 10,000 tons to navigate past the dam, and a ship lift, which allows vessels of up to 3,000 tons to bypass the ship locks and travel past the dam more quickly. At the time of its completion in late 2015, the lift, which was 120 metres (394 feet) long, 18 metres (59 feet) wide, and 3.5 metres (11 feet) deep, was the largest ship lift in the world.

Limited hydroelectric power production began in 2003 and gradually increased as additional turbine generators came online over the years until 2012, when all of the dam’s 32 turbine generator units were operating. Those units, along with 2 additional generators, gave the dam the capacity to generate 22,500 megawatts of electricity, making it the most productive hydroelectric dam in the world. In 2020 the hydroelectric plant produced 111.88 kilowatt hours, setting a new world record for annual power generation volume.

The dam also was intended to protect millions of people from the periodic flooding that plagues the Yangtze basin, although just how effective it has been in this regard has been debated. In 2020 China experienced its heaviest floods in more than three decades, and the dam’sreservoir neared maximum capacity, reaching the highest levels since it began retaining water in 2003. Officials said that the dam reduced damage and loss of life from the floods, while critics asserted that the heavy floods served to highlight the limitations of the dam as an effective flood-control tool.

History and controversy of the Three Gorges Dam

First discussed in the 1920s by Chinese Nationalist Party leaders, the idea for the Three Gorges Dam was given new impetus in 1953 when Chinese leader Mao Zedong ordered feasibility studies of a number of sites. Detailed planning for the project began in 1955. Its proponents insisted it would control disastrous flooding along the Yangtze, facilitate inland trade, and provide much-needed power for central China, but the dam was not without its detractors. Criticisms of the Three Gorges project began as soon as the plans were proposed and continued through its construction. Key problems included the danger of dam collapse, the displacement of some 1.3 million people (critics insisted the figure was actually 1.9 million) living in more than 1,500 cities, towns, and villages along the river, and the destruction of magnificent scenery and countless rare architectural and archaeological sites. There were also fears—some of which were borne out—that human and industrial waste from cities would pollute the reservoir and even that the huge amount of water impounded in the reservoir could trigger earthquakes and landslides. Some Chinese and foreign engineers argued that a number of smaller and far cheaper and less-problematic dams on the Yangtze tributaries could generate as much power as the Three Gorges Dam and control flooding equally well. Construction of those dams, they maintained, would enable the government to meet its main priorities without the risks.

Because of these problems, work on the Three Gorges Dam was delayed for nearly 40 years as the Chinese government struggled to reach a decision to carry through with plans for the project. In 1992 Premier Li Peng, who had himself trained as an engineer, was finally able to persuade the National People’s Congress to ratify the decision to build the dam, though almost a third of its members abstained or voted against the project—an unprecedented sign of resistance from a normally acquiescent body. Pres. Jiang Zemin did not accompany Li to the official inauguration of the dam in 1994, and the World Bank refused to advance China funds to help with the project, citing major environmental and other concerns.

Nevertheless, the Three Gorges project moved ahead. In 1993 work started on access roads and electricity to the site. Workers blocked and diverted the river in 1997, bringing to a close the first phase of construction. In 2003 the reservoir began to fill, the five-tier ship locks—which allowed vessels of up to 10,000 tons to navigate past the dam—were put into preliminary operation, and the first of the dam’s generators was connected to the grid, completing the second phase of construction. (Following completion of this second phase, some 1,200 sites of historical and archaeological importance that once lined the middle reaches of the Yangtze River vanished as floodwaters rose.) Construction of the main wall of the dam was completed in 2006. The remainder of the dam’s generators were operational by mid-2012, and a ship lift, which allowed vessels of up to 3,000 tons to bypass the five-tier ship locks and more quickly navigate past the dam, was completed in late 2015 and began officially operating in 2016.

dam, structure built across a stream, a river, or an estuary to retain water. Dams are built to provide water for human consumption, for irrigating arid and semiarid lands, or for use in industrial processes. They are used to increase the amount of water available for generating hydroelectric power, to reduce peak discharge of floodwater created by large storms or heavy snowmelt, or to increase the depth of water in a river in order to improve navigation and allow barges and ships to travel more easily. Dams can also provide a lake for recreational activities such as swimming, boating, and fishing. Many dams are built for more than one purpose; for example, water in a single reservoir can be used for fishing, to generate hydroelectric power, and to support an irrigation system. Water-control structures of this type are often designated multipurpose dams.

Auxiliary works that can help a dam function properly include spillways, movable gates, and valves that control the release of surplus water downstream from the dam. Dams can also include intake structures that deliver water to a power station or to canalstunnels, or pipelines designed to convey the water stored by the dam to far-distant places. Other auxiliary works are systems for evacuating or flushing out silt that accumulates in the reservoir, locks for permitting the passage of ships through or around the dam site, and fish ladders (graduated steps) and other devices to assist fish seeking to swim past or around a dam.

dam can be a central structure in a multipurpose scheme designed to conserve water resources on a regional basis. Multipurpose dams can hold special importance in developing countries, where a single dam may bring significant benefits related to hydroelectric power production, agricultural development, and industrial growth. However, dams have become a focus of environmental concern because of their impact on migrating fish and riparian ecosystems. In addition, large reservoirs can inundate vast tracts of land that are home to many people, and this has fostered opposition to dam projects by groups who question whether the benefits of proposed projects are worth the costs.

In terms of engineering, dams fall into several distinct classes defined by structural type and by building material. The decision as to which type of dam to build largely depends on the foundation conditions in the valley, the construction materials available, the accessibility of the site to transportation networks, and the experiences of the engineers, financiers, and promoters responsible for the project. In modern dam engineering, the choice of materials is usually between concrete, earthfill, and rockfill. Although in the past a number of dams were built of jointed masonry, this practice is now largely obsolete and has been supplanted by concrete. Concrete is used to build massive gravity dams, thin arch dams, and buttress dams. The development of roller-compacted concrete allowed high-quality concrete to be placed with the type of equipment originally developed to move, distribute, and consolidate earthfill. Earthfill and rockfill dams are usually grouped together as embankment dams because they constitute huge mounds of earth and rock that are assembled into imposing man-made embankments

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