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the Hoover Dam

xavier

 

 

Hoover dam sign

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Boulder dam, pre-1947; Hoover Dam 2010 [image: Google]

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introduction

the boulder canyon project
naming the dam
building the dam
lake mead - water levels
structural statistics and other interesting facts
end notes

related:

Hoover Dam Canyon Bridge or the Mike O'Callaghan-Pat Tilman Memorial Bridge

Skywalk,
Grand Canyon

The Hoover, or Boulder, Dam opened in 1935. Built as a means of counteracting the effects of the Great Depression, this ambitious project provided employment, income and hope during a dire time. As a result, both men and women migrated to this desolate and inhospitable region of southern Nevada, to find work and to make a new life.

the boulder canyon project

The Boulder Canyon Project grew out of a need for water storage and a reliable source for irrigation water, as well as flood and silt control and later also for hydroelectricity.

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Hoover dam and appurtenant works plan and cross-section
Plan and cross-section showing the dam, as well as the tunnels diverting the Colorado River, spillways and power plant

The dam in that project, at first named the Boulder Dam, would hold back water from the Colorado River, with the resulting reservoir being called Lake Mead. This artificial lake is is 110 miles long and took six years to fill. It formed what was, in the 1930s, the largest man-made lake.

The Boulder Dam, which after several name changes became the Hoover Dam, is located in Black Canyon on the Colorado River, thirty miles south-east of Las Vegas, Nevada. When built, the dam was the highest in the world, rising 727 feet [222 metres] above bedrock. Its power was also the largest in the world at the time, containing generators enough to produce over 1,368,000 kW in 1935, as much as produced by Muscle Shoals and Niagara Falls combined.

naming the dam

There was much debate over the name for this dam as it was built. Originally, the dam was to be built at Boulder Canyon, which is about 10 miles upstream and north from its final location at Black Canyon. However, the actual site was later chosen because the resulting dam would not need to be as high as at Black Canyon. Early names for this dam were Boulder Dam and Boulder Canyon Dam. Another suggested name was Black Canyon Dam.

Over the years, the dam’s name was changed for political reasons, firstly in 1930 by the Herbert Hoover administration, who changed the name from Boulder Dam to Hoover Dam. Then in 1933, the Franklin Roosevelt administration changed it back to Boulder Dam. Finally in 1947, during Harry Truman’s administration, the dam was named Hoover Dam definitively.

building the dam

postcard showing Boulder Dam construction stages

A consortium of six construction firms, Six Company Inc., was the lowest qualified bidder for the contract to build the Hoover Dam. They charged $48,890,955. The company was received incentive bonuses and would be fined for daily construction overruns of the schedule. In fact, the Hoover Dam completed almost two years ahead of schedule, thanks to a break-neck 24-hour construction rate. At the time, this was the largest construction project in American history. When finished, it was the world’s largest concrete structure (a title held until 1942).

Because the river bedrock had to be exposed, cleared of all silt and sediment, the Colorado River was diverted temporarily. Four huge diversion tunnels were dug through the canyon walls, taking the river flow around the dam site so it joined the river further downstream. When the dam was completed, the river was reverted to its original course.

High scalers, acrobatic and daring workmen swinging from cables, cleared loose rocks and made the canyon walls smooth so the dam concrete would adhere. In all, they cleared more than 137,000 cu/yd of materials from the canyon walls.


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00:26 secs High scalers working on the Boulder (Hoover) Dam.

The dam and its accompanying (appurtenant) works of power plants, tunnels, spillways and roads were fabricated from over 3,250,000 cubic yards of concrete. It was mixed on the site and transported in four or eight cubic ton buckets transported on overhead cables. The concrete was poured into huge interlocking blocks, rather like Lego blocks.

Hoover Dam partially built
Hoover Dam partially built

Because concrete gives off heat as it is made and sets, an exothermic reaction, the concrete was laid in tranches of five feet depth. Further, concrete laying was restricted to just one 5-foot addition per block in 72 hours, and no more than 7 additions per block in 30 days. Also, the height of the tallest block could not be greater that 35 feet higher than the lowest block. Additionally, a system of cooling pipes was run through each block, with the pipes, iced water run through enabling the blocks to cool and set evenly. By the end of the cooling operations in March 1935, over 159 billion B.t.u./1.6 billion joules of heat had been removed.


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lake mead - water levels

Hoover Dam holding back Lake Mead in 1991
Hoover Dam holding back Lake Mead in 1991
Lake Mead in 2007. Image: nebraskaweatherphotos.org
Lake Mead in 2007, showing the limestone ‘bathtub ring’.
Image:
nebraskaweatherphotos.org

The water level in Lake Mead, in recent years, has been falling steadily and considerably. Since 1999, the water level has dropped by about 1% annually.

In 1964, Lake Mead’s water level had fallen to only 1095.12 feet. Then, it took 19 years to recover the water holding.
In 1998, the water in Lake Mead was at a record high elevation of 1215.76 feet.
By 2007, the lake’s water level had fallen by 118 feet, with 15 feet of that occuring in 2006-7. Lake Mead then held 46% of its maximum capacity.
The January 2009 water level was 1111.1 feet.

This loss of water is caused by the continuing drought in southwestern America, and by an increasing population. Demands on water range from irrigating lettuce, onions and wheat in reclaimed corners of the Sonoran Desert to watering lawns and golf courses in conurbations from Las Vegas to Los Angeles. There, new residents install lawns, sprinklers and pools, and frequent golf courses built for their recreation in the Mojave Desert. They have moved to a region that receives 10 cm/4 ins of rain annually, about a tenth of Chicago’s annual rainfall. To these water demands are added those of the Las Vegas’s entertainment industry, where casinos and hotels have water slides and river rides.

 

structural statistics and other interesting facts

    The dam Hoover dam 1942, photo:  Ansel Adams
  • Dam type: concrete arch-gravity type (water load carried by both gravity action and horizontal arch action)
  • Dam height: 726.4 ft/221.3 m
  • Dam length: 1,244 ft/379 m
  • Width - crest: 45 ft/14 m
               - base: 660 ft/200 m
  • Number of electricity generating turbines: now 17 (increased incrementally until 1961)
  • Hydroelectric power generated: up to 2,074 MW
  • Annual power generated: approx. 4.2 billion KWh
  • Architect: Gordon B. Kaufmann, designer of Los Angeles Times Building

    Dam construction: Discharging a 16-ton bucket of concrete
  • Work started: 1931
  • First concrete poured: June 1933
  • Dam handed over and opened: 1 March, 1936
  • Concrete used: 3,250,000 cubic yards/2,600,000 cubic metres
    made from over 5 million barrels Portland cement,
    4.5 million cubic yards of aggregate, locally prepared from alluvial stones
    dam’s mass is greater than that of the Great Pyramid of Giza
  • Number of concrete blocks: approx. 215
  • Block dimensions: 5ft high, varying from 25 x 25 ft on downstream side to 60 x 60 ft on the upstream side, built in columns later grouted with concrete. The blocks had locking keys like giant Lego blocks.
  • Concrete exothermic reaction counter-measures: Concrete poured in separate columns of five-foot increments, to avoid uneven cooling and contraction. If made in one continuous pouring, the heat generated would mean the concrete would take 125 years to cool to ambient temperature.
    Over 582 miles of temporary 1-inch, thin-walled steel pipe were laid in the concrete. These carried cooling water, the pipe were later cut short and pressure grouted.
  • Cost: $49 million

    Non-concrete materials
  • Reinforcement steel: 45,000,000 lb
  • Gates and valves: 21,670,000 lb
  • Plate steel and outlet pipes: 88,000,000 lb
  • Pipe and fittings: 6,700,000 pounds/840 miles
  • Structural steel: 18,000,000 lb
  • Miscellaneous metal work 5,300,000 lb

    Workforce
  • Overall more than 21,000; 3,500 daily average, 5,251daily maximum in July 1934.
  • Average monthly salary bill/payroll: $500,000
  • Number of deaths (from causes including accidents, heat stroke, heart failure) : 112; official number: 96. None were buried in the concrete, the manufacture process of the blocks was too labour-intensive, and so too well supervised for such an occurence.

    Diversion tunnels Three-storeys of drillers to enable efficient tunnel cutting. Image: US Bureau of Reclamation
  • Four tunnels drilled through canyon walls.
  • Final tunnel diameter: 50 ft
  • Average tunnel length: 3980 ft
  • Tunnel lining: 300,000 cubic yards of concrete - thickness of 3 feet; so tunnels were, in fact, drilled to 56 ft diameter
  • Capacity: 200,000 cubic feet/1.5 million gallons water per second
  • Diversion started: 14 November 1932
  • Tunnel stopping: concrete in one-third their length
  • Current tunnel uses:
    inner tunnels: contain 30-ft steel pipes (penstocks) to connect reservoir intake towers power plant and canyon wall outlet works.
    outer tunnels, downstream halves: spillway outlets.

    Intake towers View of the Hoover Dam and its intake towers before the dam was filled. Image: US Bureau of Reclamation
  • Four reinforced-concrete structures located above the dam, two on each side of the canyon
  • Tower diameter: 82 feet at the base, 63 feet 3 inches at the top, and 29 feet 8 inches inside
  • Tower height: 395 feet
  • Material content for each tower: approx. 23,420 cu. yards concrete and 3,825,000 lbs steel
  • Each tower controls one quarter of the water supply for the power plant turbines

    Lake Mead Satellite image of Lake Mead, Novemebr 1985
  • Maximum depth: 590 ft/180 m
  • Capacity: 35.2 km3/28,500,000 acre ft
  • Surface area: 247 sq mi/640 km2
  • Catchment area: 167,800 sq mi/435,000 km2

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end notes

  1. 8 cubic yards of concrete weighs approximately 16 tons.
    Thus, 3,250,000 cubic yards of concrete weighs about 6.5 million tons.

 


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