Hoover Dam
A Very Impressive Monument To Engineering & Construction
Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Arizona and Nevada. When completed in 1936, it was both the world's largest hydroelectric power generating station and the world's largest concrete structure. It was surpassed in both these respects by the Grand Coulee Dam in 1945. It is currently the world's 38th-largest hydroelectric generating station.
This dam, located 30 mi (48 km) southeast of Las Vegas, Nevada, is named after Herbert Hoover, who played an instrumental role in its construction, first as the Secretary of Commerce, and then later, as the President of the United States. Construction began in 1931, and was completed in 1936, a little more than two years ahead of schedule. The dam and the power plant are operated by the Bureau of Reclamation of the U.S. Department of the Interior. Listed on the National Register of Historic Places in 1981, Hoover Dam was designated a National Historic Landmark in 1985.
Lake Mead is the reservoir created by the dam, named after Elwood Mead, who oversaw the construction of the dam.
The dam is protected against overtopping by two spillways. The spillway entrances are located behind each dam abutment, running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weir with each spillway containing four 100 ft (30 m) long and 16 ft (4.9 m) high steel drum gates. Each gate weighs five million pounds and can be operated manually or automatically. Gates are raised and lowered depending upon water levels in the reservoir and flood conditions. The gates cannot completely stop water from entering the spillway but help maintain an extra 16 ft. of lake level.
Water flowing over the spillways drops sharply into either of 600 ft (180 m) long, 50 ft (15 m) wide spillway tunnels before connecting to part of the construction diversion tunnels, and reenters the main river channel below the dam. This complex spillway entrance arrangement combined with the approximate 700 ft (210 m) elevation drop from the top of the reservoir to the river below is a difficult engineering problem and poses several design challenges. The overall spillway capacity was empirically verified in post construction tests in 1941. This test also showed that the spillway tunnels could be damaged from cavitation created by the high velocity flow when running near full volume. After further damage was incurred during use in six weeks in the summer of 1983, the tunnel linings were repaired and the spillway tunnel design was modified to minimize cavitation potential. Nevertheless, each spillway tunnel can handle 200,000 cu ft/s (5,700 m3/s), similar to the flow of Niagara Falls.
The large spillway tunnels have only been used twice in the history of the dam. In addition to testing in 1941, the spillways were used because of flooding in 1983. The spillway gates were also used in 1999 to hold water behind the dam, due to heavy precipitation in the Lake Mead watershed that increased water levels. Wiki
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