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Hoover Dam


U.S.A. facts & history in brief        U.S.A. Map

Hoover Dam in the Black Canyon of the Colorado River, in the Arizona State, in the United States is one of the highest concrete dams in the world.
The Colorado River originates in the snow-capped mountains of north central Colorado and winds southwest for more than 1,400 miles before reaching the Gulf of California.
The river and its tributaries, the Green, the Gunnison, the San Juan, the Virgin, the Little Colorado, and the Gila rivers - are called the "Colorado River Basin".
These rivers drain 242,000 square miles in the United States, or one-twelfth of the country's continental land area, and 2,000 square miles in Mexico. Seven western states and Mexico have interests in the Colorado River Basin.
The Colorado River Compact apportioned water to two basins, Upper (Arizona, Colorado, New Mexico, Utah, and Wyoming) and Lower Basin States (California, Arizona, and Nevada), each the use of 7,500,000 acre-feet of water per year from the Colorado River system in perpetuity.
The United States and Mexico signed a treaty in 1944, guaranteeing Colorado River water annually.
The dam is part of the Boulder Canyon Project, consisting of a dam, a hydroelectric power plant, and a reservoir (Lake Mead).
The Dam controls floods of the Colorado River and supplies domestic and irrigation water and electric power for a large area of the Pacific Southwest, including Las Vegas and Los Angeles.
The 221 metres high and 379 metres long Dam was built during the 'Great Depression' years, and was completed in 1936.
It was a giant project and is still 20th highest dam in the world at, 226 metres.
The Dam is in Black Canyon on the Colorado River, about 30 miles southeast of Las Vegas, Nevada.
The Dam weighs more than 6,600,000 tons and it is a concrete arch-gravity type, in which the water load is carried by both gravity action and horizontal arch action.
The maximum water pressure at the base of the dam is about 10000 kg per sq metres.
Over three million cubic metres of concrete was used in the dam, using more than 5 million barrels of cement.
To dissipate the chemical heat caused by the setting cement in the dam more than 936 kilometres of 2.5 cm steel pipe was embedded in the concrete and circulating ice water through it from a refrigeration plant, that could produce 1,000 tons of ice in 24 hours.
The dam was built in blocks or vertical columns varying in sizes.
Adjacent columns were locked together by vertical keys on the radial joints and horizontal keys on the circumferential joints.
Concrete placement in any one block was limited to 5 feet in 72 hours.
After the concrete was cooled, a cement and water mixture (Grout) was forced into the spaces between the columns by the contraction of the cooled concrete to form a monolithic structure.
The first partial surveys of the over 2250 km Colorado River, the third longest river in the United States, were made by Major John Wesley Powell in the late 1860s and the early 1870s.
In 1920,as the federal Water Power Act was enacted, more than 1200 km of the river was still unsurveyed and uncharted.
In 1921, four 18-foot, special, wooden, kayak-like boats, the Grand, the Glen, the Boulder and the Marble were designed and constructed to withstand the wear and tear of the turbulent stretches of the river.
They were made of oak, spruce and cedar wood, and featured watertight compartments in the bow and stern to keep them afloat if they overturned.
In September 1921, Geological Survey and Edison Company engineers retraced much of Major Powell's original route down the Green and Colorado Rivers, to develop a topographic map of the area that would be flooded if a dam was constructed at Glen Canyon, just above the Grand Canyon encountering several rapids in the uncharted waters of the upper Colorado River.
The survey took more than two years due to seasonal low waters and flooding.
After the survey work and actual siting and planning of the reservoir and dam access highways, Boulder City for the construction staff, a railway line from Las Vegas to Boulder City and to the dam site and a nearly 360 km long power transmission line from San Bernardino, California, to the dam site to supply energy for the construction had to be constructed.
The dam's foundation and abutments are "andesite breccia", rock of volcanic origin.
The rock is hard and very durable.
All loose rock had to be removed from the canyon's wall, before construction could begin by the High-Scalers, whose job was to climb down the canyon walls on ropes and working with jackhammers (20 kg) and dynamite they had to strip away the loose rock.
The broken rocks sometimes had to be levered free using crowbars.
They were all agile men, unafraid to swing out over empty space on slender ropes.
It was hard and dangerous work, perhaps the most physically demanding work on the entire project.
Live air hoses, electrical lines, bundles of drill steel festooned the cliffs.
The scalers laden with tools and water bags had to carefully pick their way through the resulting maze.
The danger from falling rocks and dropped tools was extreme.
The most common cause of death during the building of the dam was being hit by falling objects.
The men began making improvised hard hats for themselves by coating cloth hats with coal tar.
These "hard-boiled hats" were extremely effective.
Before construction could begin on the dam, to isolate the construction site, and protect it from flooding, two cofferdams were constructed.
Construction of the upper cofferdam began before the river was diverted.
The Colorado River was diverted around the dam site through four 15 metres diameter tunnels, two on each side of the river drilled through the canyon walls.
The tunnel, with a total length of about 5 km, were excavated to 18 metres and lined with 1 metre thick concrete.
The tunnels could carry over 6 million litres of water per second.
The Nevada and Arizona States border runs and marked in the middle of the Colorado River and the Dam.
The first diversion tunnels were built on the Arizona side first.
There was also a rock barrier built just over 100 metres down river from the lower cofferdam.
A good supply of aggregate had to be found and a concrete batching plant had to built before construction could begin in earnest.
Another concrete batching plant had to built too at a later stage.
The dam was built in five years.
The contractors were allowed 7 years, but concrete placement in the dam was completed in 1935, and all features were completed by March 1936.
There were 96 industrial fatalities during the construction of the dam including deaths from drowning, blasting, falling rocks or slides, falls from the canyon walls, struck by heavy equipment, truck accidents, but not including deaths from heat, pneumonia, heart trouble, etc.
A Bureau of Reclamation surveyor, J.G. Tierney fell from a barge in the Colorado River and drowned in 1922.
Thirteen years later his son J.G. Tierney, fell to his death, from one of the intake towers, in 1935.
The dam needed a reservoir for flood control and ensuring an adequate supply of water all year around.
The reservoir now called Lake Mead is at 375 metres above sea level and about 5 metres above the spillways storing about 36,702,300,000 cubic metres of water.
It is about 185 kilometres long and 180 metres deep and one of the world's largest artificial lakes.
They are four reinforced-concrete structures located above the dam, two on each side of the canyon supplying the of water for the powerplant turbines, through 10 metres diameter penstocks (pipes) installed in concrete-lined tunnels.
As nearly everything like tunnels the spillways run on each side of the border of the two states and are concrete-lined open channels about over 200 metres long, 50 metres wide, and 60 metres deep on each canyon wall.
The U-shaped powerplant structure is at the base of the dam.
High speed lifts ascend the nearly 50 storeys into the dam, without reaching its base.
The concrete base is 200 metres thick.
There are 17 main turbines in Hoover Powerplant.
The original turbines were all replaced between 1986 and 1993.
This includes the two station (Arizona and Nevada) service units, which are rated at 2,400 kilowatts each.
The dam was originally known as the Boulder Dam.
It was renamed Hoover Dam to honour President Hoover.

Many thanks to the Bureau of Reclamation's pamphlets.

Hui Chin and I visited Hoover Dam and Lake Mead on the way to the Grand Canyon.
It is something Gigantic and many films were made to impress people.
I, as a very mechanically minded person, who likes anything that ticks or moves or do things in general, was impressed by it and I tried to learn about it as much as I could.

You can click on these photos for an enlargement.

Hoover Dam Hoover Dam Hoover Dam Hoover Dam

You can click on these photos for an enlargement.

Hoover Dam Hoover Dam Hoover Dam Hoover Dam

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