With 22,500 MW of installed capacity, the Three Gorges Dam is the largest power station of any kind in the world. It is a concrete gravity dam across the Yangtze River at Sandouping, in the Yiling District of Yichang, Hubei province, in central China, just downstream of the Three Gorges that give it its name. The wall is 2,335 metres long and rises to 185 metres above sea level. Construction began on 14 December 1994, the dam body was finished in 2006, and the power plant became fully operational in July 2012. It produced a world-record of about 112 TWh of electricity in 2020, and its reservoir stretches about 660 km upstream. Its purposes are flood control on the Yangtze, hydropower and better navigation, and it forced the relocation of well over a million people.
22,500 MW: Thirty-Two Turbines and Two Small Ones
The headline figure is simple arithmetic. The plant has 34 generators: 32 main units of 700 MW each and two 50 MW units that power the plant itself. Fourteen main units sit on the north side of the dam, twelve on the south side, and six more in an underground power plant cut into the mountain south of the dam. Each main generator weighs about 6,000 tonnes and is driven by a Francis turbine about 10 metres across, turning at 75 revolutions per minute under a design head of 80.6 metres. Peak efficiency reaches 96.5 per cent.
The units were built by two international consortia paired with Chinese manufacturers: Alstom, ABB and Kvaerner with Harbin Motor, and Voith, General Electric and Siemens with Oriental Motor, under technology-transfer agreements signed with the contracts. The first north-side generator, No. 2, started on 10 July 2003. In December 2007 the plant reached 14.1 GW and overtook Itaipu, on the Brazil–Paraguay border, as the largest hydropower station on Earth. The last main unit, No. 27, finished its final test on 23 May 2012, and the whole plant was running by July 2012.
From Sun Yat-sen in 1919 to a 67.75 Per Cent Vote in 1992
The idea is more than a century old. Sun Yat-sen proposed a Yangtze dam capable of 30 million horsepower, about 22 GW, in The International Development of China in 1919, which turned out to be close to the capacity finally built. Chiang Kai-shek’s Nationalist government began preliminary planning in 1932, and in 1944 John L. Savage, chief design engineer of the United States Bureau of Reclamation, surveyed the site and drew up a proposal. Some 54 Chinese engineers went to the United States for training, but the civil war ended that effort.
Mao Zedong backed the project after 1949 but built the smaller Gezhouba Dam downstream at Yichang first. Economic upheaval, including the Great Leap Forward and the Cultural Revolution, slowed progress for years, and plans were revived only in the 1980s, when the Communist Party proposed starting construction in 1986. When the National People’s Congress finally voted in 1992, the result was unusually divided for that body: of 2,633 delegates, 1,767 voted in favour, 177 against, 664 abstained and 25 did not vote, an approval rate of 67.75 per cent.
2,335 Metres Long, 27.2 Million Cubic Metres of Concrete
The structure relies on mass rather than an arch. The wall is 2,335 metres long, its top stands at 185 metres above sea level, and the concrete rises 181 metres above its rock foundation. Building it took 27.2 million m³ of concrete and 463,000 tonnes of steel, and moved about 102.6 million m³ of earth. When the reservoir is at its maximum of 175 metres, the water behind the dam stands 110 metres higher than the river below it.
About 80 hairline cracks appeared after the reservoir was first filled. An expert panel still gave the project an overall good-quality rating, reporting that all 163,000 concrete units had passed testing and that deformation stayed within design limits.
112 TWh in 2020, and Why Capacity Is Not Output
Capacity measures how much power a plant can produce at once; generation measures how much it actually produces in a year. The Three Gorges plant was designed for 88.2 TWh a year. It generated 98.1 TWh in 2012, the first year with all 32 main units running, which was about 14 per cent of China’s hydroelectric output that year. It produced 101.6 TWh in 2018. Between 2012 and 2021 it averaged 97.22 TWh a year, against 89.22 TWh at Itaipu. The heavy 2020 monsoon pushed output to about 112 TWh, beating Itaipu’s 2016 record of about 103 TWh.
The gap between Three Gorges and Itaipu is much smaller in energy than in capacity because the Yangtze is seasonal. From November to May, output is limited by river flow. On 30 June 2009, by contrast, all 28 generators then installed were running but produced only 16,100 MW, because flood season lowers the head of water available. Measured against China’s demand, the dam’s share has shrunk: planners once expected it to supply 10 per cent of the country’s electricity, but in 2024 it supplied less than 1 per cent of the 9,852.1 TWh China used. The government also reported that the full construction cost had been paid back by 20 December 2013.
Getting that power to users took its own network, finished in December 2007, a year ahead of schedule, at a cost of about 34.4 billion yuan. Nine provinces and two cities take electricity from the dam. Direct-current lines carry 3,000 MW each to Shanghai, to Changzhou and, over the HVDC Three Gorges–Guangdong line, to the South China grid, while alternating-current lines with a combined 12,000 MW feed the Central China grid.
660 Kilometres of Reservoir and 22 Cubic Kilometres for Floods
At full level the reservoir averages about 660 km long and 1.12 km wide, holds 39.3 km³ of water and covers 1,045 km², of which 632 km² was previously land. The water reached the design level of 175 metres for the first time on 26 October 2010. Each year it is drawn down to 145 metres between December and March, which adds flow to the river in the dry season and makes room for summer floods.
Flood control was the reason most often given for the dam. The Yangtze flood of 1954 covered 193,000 km², killed 33,167 people and forced almost 18.9 million to move; Wuhan stayed under water for more than three months. The reservoir has 22 km³ of flood storage, which planners said would cut the frequency of major downstream floods from once in 10 years to once in 100. During the July 2010 floods inflow peaked at 70,000 m³ per second, higher than in the 1998 flood, and the dam held outflow to 40,000 m³ per second. It cannot protect against every flood, though: large tributaries that join below the dam, including the Xiang, Han and Gan, are outside its reach.
159.65 Million Tonnes Through the Locks in 2022
Before the dam, the gorges could handle about 18 million tonnes of freight a year. The project added two flights of five-step ship locks, one for traffic going upstream and one for traffic going downstream. Each chamber is 280 metres long, 35 metres wide and 5 metres deep, takes vessels of up to 10,000 tonnes, and a full passage takes about four hours. Traffic has far outrun the original design of 100 million tonnes a year: in 2022, 159.65 million tonnes passed through.
For smaller vessels there is a faster route. The ship lift, designed by the German firm Lahmeyer and operating since 2016, raises or lowers boats of up to 3,000 tonnes through 113 metres in a basin measuring 120 by 18 metres. A transit takes 30 to 40 minutes instead of three or four hours, and the lift must work even when the upper water level varies by 30 metres and the lower by 12.
1.24 Million Residents Moved and 723 Sites Excavated
The largest number linked to the dam is a human one. Planners estimated that 13 cities, 140 towns and 1,350 villages would be partly or completely flooded. By June 2008 China had moved 1.24 million residents, some as far away as Gaoyang in Hebei province; overall estimates range from 1.13 to around 1.4 million. Resettlement took a large share of the budget: of the 148.4 billion yuan spent by the end of 2008, 68.6 billion yuan went on relocation, more than on construction. Archaeologists worked through 723 sites and surveyed 346 more, recovering 200,000 artefacts, many now in the Chongqing China Sanxia (Three Gorges) Museum.
The environmental costs are still being counted. The reservoir traps sediment that once rebuilt the plain on which Shanghai, more than 1,600 km downstream, stands. Earthquakes around the reservoir rise and fall with the water level, and landslides are frequent, with 97 significant ones in the first four months of 2010 alone. The Yangtze river dolphin, or baiji, is now extinct, and Chinese government scholars have blamed the dam directly. The upstream Jinsha River dams, including Baihetan and Xiluodu, were built partly to trap sediment before it reaches Three Gorges.
For how the dam fits into the wider river, see our Yangtze River guide; for the plant it overtook in 2007, read about Itaipu Dam on the Paraná; and for proof that the biggest power station is not the biggest reservoir, compare it with Africa’s Kariba Dam, whose lake holds about four times as much water.