The Three Gorges Dam, built along the Yangtze River in China is the largest hydroelectric dam in the world with a generating capacity of 22,500 megawatts. It is 2,335m long at a height of 181m and creates a 660km long reservoir.
A Vision from 1919
The idea for the dam was first proposed in 1919 by Sun Yat-sen, often considered the father of modern China. He believed the structure could protect river communities from deadly floods. The construction of the dam began 74 years later, in 1993.
Millions of people, billions of Dollars
To keep the people of China safe, 1.3 mn people had to be relocated due to earthquakes provoked by the dam. As per media reports, over a hundred workers died during the construction. The economic cost of the project was reported to be around $24 bn.
Can it slow down Earth's rotation?
The dam can hold 39 trillion kilograms of water, with the river rising 175 metres above sea level. The high mass of water being funnelled through the dam creates an effect called 'moment of inertia', due to which Earth loses a bit of momentum when rotating.
And then the moment slowed down...
NASA has calculated that the dam can slow the rotation of Earth, making the day longer by 0.06 microseconds and making the Earth slightly more round in the middle and flat on the poles. It can make the Earth slightly more round in the middle and flat on the top, shifting the pole position by about 2cm (0.8 inches).
60 Eiffel Towers
The construction of the dam used 463,000 tons of steel, enough to make over 60 Eiffel Towers of steel.
CONTROVERSY OVER THE MAKING OF THE DAM
The proposal for the Three Gorges Dam was first proposed in the 1920s by officials of the Chinese Nationalist Party; in 1953, Chinese leader Mao Zedong requested feasibility studies of several potential sites. The project's preliminary planning stages started in 1955. Its supporters said that the dam would prevent catastrophic floods along the Yangtze, improve inland trade, and provide central China access to much-needed electricity, while its opponents voiced concerns about the project's environmental impact. The Three Gorges project has been the target of detractors ever since its inception as a concept.
Critical issues included the potential for dam failure, the relocation of over 1.3 million people who lived in more than 1,500 cities, towns, and villages along the river, and the ruin of stunning landscapes and many important architectural and archaeological treasures. There were also concerns, some of which proved to be valid, that the reservoir would become polluted by human and industrial waste from nearby cities, and that the massive volume of water held there may cause earthquakes and landslides.
Several Chinese and European engineers have maintained that a series of smaller dams on Yangtze tributaries might provide as much electricity as the Three Gorges Dam and control floods just as effectively, for a fraction of the cost and with a fraction of the problems. They argued that the government's top goals could be met if the dams were built.
The Chinese government had a hard time deciding whether or not to move through with plans for the Three Gorges Dam because of these issues, which pushed back construction by about 40 years. Premier Li Peng, who had studied engineering, was successful in 1992 in convincing the National People's Congress to approve the dam's construction despite the fact that over a third of the congressmen either didn't vote or voted against the plan. World Bank declined to advance China's cash to aid with the project due to serious environmental and other concerns, and President Jiang Zemin did not attend the official opening of the dam alongside Li in 1994.
The Three Gorges project continued nonetheless. Building the roads and installing the power to the site began in 1993. In 1997, workers completed the first phase of development by damming and rerouting the river. The second phase of construction was finished in 2003 when the reservoir began to fill, the five-tier ship locks (which enabled boats of up to 10,000 tonnes to pass through the dam) were placed into preliminary operation, and the first of the dam's generators was linked to the grid.
(After this second phase was finished, the floodwaters swept away 1,200 historical and archaeological sites that had formerly lined the middle reaches of the Yangtze River.) The dam's primary wall was built and finished in 2006. By the middle of 2012, all of the dam's generators were running, and by the end of 2015, a ship lift had been installed and was in service, allowing ships of up to 3,000 tonnes to easily go over the dam.
Environmentalists have warned that the dam will reduce downstream nutrient and sediment flow, seriously impacting neighbouring river and seacoast ecosystems.
It also poses a threat to coastal fishing grounds and subjects tidal wetlands to increased erosion.
The dam catalysed enhanced upstream wastewater treatment surrounding Chongqing and its suburban districts. According to the Ministry of Environmental Protection, as of April 2007, more than 50 new facilities could treat 1.84 million tonnes per day, 65 per cent of the overall requirement.
About 32 landfills were added, which could manage 7,664.5 tonnes of solid waste per day. Over one billion tonnes of wastewater are dumped annually into the river, which was more likely to be carried away before the reservoir was established. This has left the water appearing sluggish, dirty and murky.
Reportedly, 200 tons of explosives were used to demolish the final Three Gorges cofferdam- a temporary construction to help builders finish the dam's main wall.
At peak construction, the dam employed 26,000 Chinese and foreign employees.