Hoover Dam: -

Hoover Dam, formerly called Boulder Dam, dam in Black Canyon on the Colorado River, at the Arizona-Nevada border, U.S. Constructed between 1930 and 1936, it is the highest concrete arch dam in the United States. It impounds Lake Mead, which extends for 115 miles (185 km) upstream and is one of the largest artificial lakes in the world. The dam is used for flood and silt control, hydroelectric power, agricultural irrigation, and domestic water supply. It is also a major sightseeing destination, with some seven million visitors a year, almost one million of whom go on tours through the dam.

Hoover Dam is 726 feet (221 metres) high and 1,244 feet (379 metres) long at the crest. It contains 4,400,000 cubic yards (3,360,000 cubic metres) of concrete. Four reinforced-concrete intake towers located above the dam divert water from the reservoir into huge steel pipes called penstocks. The water, after falling some 500 feet (150 metres) through the pipes to a hydroelectric power plant in the base of the dam, turns 17 Francis-type vertical hydraulic turbines, which rotate a series of electric generators that have a total power capacity of 2,080 megawatts. Nearly half of the generated electric power goes to the Metropolitan Water District of Southern California, the city of Los Angeles, and other destinations in southern California; the rest goes to Nevada and Arizona. The dam, power plant, and reservoir are owned and managed by the U.S. Department of the Interior’s Bureau of Reclamation.

The Three Gorges Dam: -

Three Gorges Dam, dam on the Yangtze River (Chang Jiang) just west of the city of Yichang in Hubei province, China. 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.

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. 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. 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.