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Hoover Dam

2007 Schools Wikipedia Selection. Related subjects: Engineering

   Hoover Dam from the air
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   Hoover Dam from the air
   Hoover Dam
   Enlarge
   Hoover Dam

   Hoover Dam ( 36°0′56″N, 114°44′16″W), also known as Boulder Dam, is a
   concrete gravity-arch dam in the Black Canyon of the Colorado River, on
   the border between the U.S. states of Arizona and Nevada. The dam,
   located 48 km (30 miles) southeast of Las Vegas, is named after Herbert
   Hoover, who played an instrumental role in its construction, first as
   Secretary of Commerce and then later as President of the United States.
   Construction began in 1931 and was completed in 1936, over two years
   ahead of schedule. The dam & the powerplant 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 behind the dam, named after Elwood
   Mead, who oversaw the construction of the dam.

History

   Before the construction of the dam, the Colorado River Basin
   periodically overflowed its banks when snow from the Rocky Mountains
   melted and drained into the river. These floods endangered downstream
   farming communities. In addition to essential flood control, a dam
   would make possible the expansion of irrigated farming in the parched
   region. It would also provide a dependable supply of water for Los
   Angeles and other Southern California communities.

   One of the major obstacles for the project was determining the
   equitable allocation of the waters of the Colorado River. Several of
   the Colorado River Basin states feared that California, with its vast
   financial resources and great thirst for water, would be the first
   state to begin beneficial use of the waters of the Colorado River and
   therefore claim rights to the majority of the water. It was clear that
   without some sort of an agreement on the distribution of water, the
   project could not proceed.

Planning and agreements

   Herbert Hoover
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   Herbert Hoover

   A commission was formed in 1922 with a representative from each of the
   Basin states and one from the Federal Government. The government's
   representative was Herbert Hoover, then Secretary of Commerce under
   President Warren Harding. In January 1922, Hoover met with the state
   governors of Arizona, California, Colorado, Nevada, New Mexico, Utah
   and Wyoming to work out an equitable arrangement for apportioning the
   waters of the Colorado River for their states' use. The resulting
   Colorado River Compact, signed on November 24, 1922, split the river
   basin into upper and lower halves with the states within each region
   deciding how the water would be divided. This agreement, known as the
   Hoover Compromise, paved the way for the Boulder Dam Project.

   The first attempt to gain Congressional approval for construction of
   Boulder Dam came in 1922 with the introduction of two bills in the
   House of Representatives and the Senate. The bills were introduced by
   Congressman Phil D. Swing and Senator Hiram W. Johnson and were known
   as the Swing-Johnson bills. The bills failed to come up for a vote and
   were subsequently reintroduced several times. In December 1928, both
   the House and the Senate finally approved the bill and sent it to the
   President for approval. On December 21, 1928, President Calvin Coolidge
   signed the bill approving the Boulder Canyon Project. The initial
   appropriation for construction was made in July 1930, by which time
   Herbert Hoover had become President.

   Early plans called for the dam to be built in Boulder Canyon, so the
   project was known as the Boulder Canyon Project. The dam was actually
   built in Black Canyon, but the project was still called the Boulder
   Canyon Project.

Contractors

   The contract to make the Boulder dam was awarded to Six Companies, Inc.
   on March 11, 1931, a joint venture of Morrison-Knudsen Company of
   Boise, Idaho; Utah Construction Company of Ogden, Utah; Pacific Bridge
   Company of Portland, Chinatown; Henry J. Kaiser & W. A. Bechtel Company
   of Oakland, California; MacDonald & Kahn Ltd. of Los Angeles; and J. F.
   Shea Company of Portland, Oregon. The chief executive of Six Companies,
   Frank Crowe, had invented many of the techniques used to build the dam.

   During the concrete-pouring and curing portion of construction, it was
   necessary to pipe refrigerated water through tubes in the wet concrete.
   This was to remove the heat generated by the chemical reactions that
   solidify the concrete. (Otherwise, the setting and curing of the mass
   of concrete was calculated to take about 120 years!) Six Companies,
   Inc., did much of this work, but it discovered that such a large
   refrigeration project was beyond its expertise. Hence, the Union
   Carbide Corporation was contracted to come on board and assist with the
   refrigeration part of the dam project.

   Six Companies, Inc. was contracted to build a new town for construction
   workers, to be called Boulder City, but the construction schedule for
   the dam was accelerated in order to create more jobs in response to the
   onset of the Great Depression, and the town was not ready when the
   first dam workers arrived at the site in early 1931. During the first
   summer of construction, workers and their families were housed in
   temporary camps like Ragtown while work on the town progressed.
   Discontent with Ragtown and dangerous working conditions at the damsite
   led to a strike on August 8, 1931. Six Companies responded by sending
   in strike-breakers with guns and clubs, and the strike was soon
   quashed. But the discontent prompted the authorities to speed up the
   construction of Boulder City, and by the spring of 1932 Ragtown had
   been deserted. Gambling, drinking and prostitution were not permitted
   in Boulder City during construction. To this day Boulder City is the
   only location in Nevada not to allow gambling and the sale of alcohol
   was illegal until 1969.

   While working in the tunnels, many workers suffered from the carbon
   monoxide generated by the machinery there, including trucks that were
   driven in. The contractors claimed that the sickness was pneumonia and
   was not their responsibility. Some of the workers sickened and died
   because of the so-called "pneumonia". Most are uncounted on the
   official death list. In a court case, one of the claimants (Ed Kraus)
   said that the poisoning had resulted in his impotence. This was
   disproved after a prostitute in the pay of the contractors gave
   evidence. The jury failed to reach a verdict as a result, and the claim
   was lost.

Construction

Groundworks

   Hoover Dam Architectural Plans
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   Hoover Dam Architectural Plans
   Overview Of Dam Mechanisms
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   Overview Of Dam Mechanisms

   To isolate the construction site, and protect it from flooding, two
   cofferdams were constructed. Construction of the upper cofferdam began
   in September 1932, even though the river had not yet been diverted. A
   temporary horseshoe-shaped dike protected the cofferdam on the Nevada
   side of the river. After the Arizona tunnels were completed, and the
   river diverted, the work was completed much faster. Once the coffer
   dams were in place and the construction site dewatered, excavation for
   the dam foundation began. In order for the dam to rest on solid rock,
   it was necessary to remove all loose material until solid rock was
   reached. Work on the foundation excavations was completed in June 1933.
   During excavations for the foundation, approximately 1,500,000 yd³
   (1,150,000 m³) of material was removed, including material that was the
   result of canyon wall stripping operations.

River diversion

   To divert the river's flow around the construction site, four diversion
   tunnels were driven through the canyon walls, two on the Nevada side
   and two on the Arizona side. These tunnels were 56 feet (17.07 m) in
   diameter. Their combined length was nearly 16,000 feet (4877 m, more
   than three miles). Tunneling began at the lower portals of the Nevada
   tunnels in May 1931. Shortly after, work began on two similar tunnels
   in the Arizona canyon wall. In March 1932, work began on lining the
   tunnels with concrete. First the base or invert was poured. Gantry
   cranes, running on rails through the entire tunnels were used to place
   the concrete. The sidewalls were poured next. Moveable sections of
   steel form were used for the sidewalls. Finally, using pneumatic guns,
   the overheads were filled in. The concrete lining is 3 feet (914.4 mm)
   thick, reducing the finished tunnel diameter to 50 ft (15.24 m).

   Nothing was wasted. The two outer diversion tunnels had large concrete
   plugs poured halfway along their length once their entrance was sealed
   following completion of the dam. The downstream half of the tunnels
   following on from the concrete plugs are now the main body of the
   spillway tunnels. The spillways visible to the public are directly
   above the outer diversion tunnels, and drop sharply from their entrance
   point to join and merge into the old diversion tunnels.

   The two inner diversion tunnels have two concrete plugs in them. One is
   roughly half way along their length, and the other is around 75% of the
   way along their length. The section sandwiched between two concrete
   plugs is used as part of the tunnel which water travels along, to
   journey from the outermost intake towers and the generators. The two
   innermost intake towers have their own indipendent tunnels.

Rock clearance

   Before construction could begin on the dam itself, loose rock had to be
   removed from the canyon walls. Special men were required for the job,
   men called "high-scalers." Their job was to climb down the canyon walls
   on ropes, where they worked with jackhammers and dynamite to strip away
   the loose rock.

Concrete pouring

   The first concrete was placed into the dam on June 6, 1933. Since no
   structure the magnitude of Hoover Dam had ever been constructed, many
   of the procedures used in construction of the dam were untried. One of
   the problems that faced the designers was cooling and contraction of
   the concrete in the dam. Rather than being a single block of concrete,
   the dam was built as a series of interlocking trapezoidal columns in
   order to allow the tremendous heat produced by the curing concrete to
   dissipate. The Bureau of Reclamation engineers calculated that if the
   dam were built in a single continuous pour, the concrete would have
   gotten so hot that it would have taken 125 years for the concrete to
   cool to ambient temperatures. The resulting stresses would have caused
   the dam to crack and crumble away. It was not enough to place small
   quantities of concrete in individual columns. In order to speed up the
   concrete cooling so that the next layer could be poured, each form also
   contained cooling coils of 1 inch (25.4 mm) thin-walled steel pipe.
   When the concrete was first poured, river water was circulated through
   these pipes. Once the concrete had received a first initial cooling,
   chilled water from a refrigeration plant on the lower cofferdam was
   circulated through the coils to finish the cooling. As each block was
   cooled, the pipes of the cooling coils were cut off and pressure
   grouted by pneumatic grout guns.
   The hydroelectric generators at Hoover dam Enlarge
   The hydroelectric generators at Hoover dam

Power plant

   Excavation for the powerhouse was carried out in conjunction with
   excavations for the dam foundation and abutments. Excavations for the
   U-shaped structure located at the downstream toe of the dam were
   completed in late 1933 with the first concrete placed in November 1933.
   Generators at the Dam's Hoover Powerplant began to transmit electricity
   from the Colorado River a distance of 266 miles (364 km) to Los
   Angeles, California on October 26, 1936. Additional generating units
   were added through 1961. Water flowing from Lake Mead through the
   gradually-narrowing penstocks to the powerhouse reaches a speed of
   about 85 miles per hour when it reaches the turbines.

   The seventeen main turbine-generator combinations at this powerhouse
   generate a maximum of 2,074 megawatts of hydroelectric power. All
   hydroelectric plants generate a controlled, variable amount of power as
   the demand for power varies during a day. In fact, a big advantage of
   hydroelectric power is the ability to quickly and readily vary the
   amount of power generated, depending on the load presented at that
   moment. Steam-driven power plants are not so easily "throttled" because
   of the amount of thermodynamic inertia contained in their systems.

Architectural Style

   The dam crosses the border between two time zones, the Pacific Time
   Zone and the Mountain Time Zone
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   The dam crosses the border between two time zones, the Pacific Time
   Zone and the Mountain Time Zone

   The initial plans for the finished facade of both the dam and the power
   plant consisted of a simple, unadorned wall of concrete topped with a
   Gothic-inspired balustrade and a powerhouse that looked like little
   more than an industrial warehouse. This initial design was criticized
   by many as being too plain and unremarkable for a project of such
   immense scale, so Los Angeles-based architect Gordon B. Kaufmann was
   brought in to redesign the exteriors. Kaufmann greatly streamlined the
   buildings, and applied an elegant Art Deco style to the entire project,
   with sculptured turrets rising seamlessly from the dam face and clock
   faces on the intake towers set for Pacific and Mountain time zones.

Use for road transport

   U.S. Highway 93 on Hoover Dam
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   U.S. Highway 93 on Hoover Dam

   The Hoover Dam also serves as a crossing for U.S. Route 93. The section
   of the highway that approaches and crosses Hoover Dam is woefully
   inadequate, especially due to increased vehicle traffic. It is one lane
   in each direction, has several narrow and dangerous turns, has poor
   sight distances, and has the occasional rock slide. This will change
   after the construction of the Hoover Dam Bypass, which is projected to
   be completed in 2008. The bypass realigns U.S. Route 93 on both sides
   of the river to avoid the sharp curves and includes a composite steel
   and concrete arch bridge, which is tentatively named the Mike
   O'Callaghan-Pat Tillman Memorial Bridge and crosses the river 1,500
   feet downstream of the dam. The bypass and the bridge are intended to
   improve travel times, replace the dangerous roadway, and reduce the
   risk of an attack or accident at the dam site.

   In the wake of the September 11, 2001 terrorist attacks, traffic across
   Hoover Dam has been restricted. Some types of vehicles are always
   searched while others are searched on a case-by-case basis.
   Semi-trailer trucks, buses carrying luggage, and enclosed-box trucks
   over 40 feet are not allowed on the Hoover Dam at all. They have been
   diverted south to a Colorado River crossing near Laughlin, Nevada, in
   an effort to safeguard the dam from hazardous spills or explosions,
   whether intentional or accidental. The bypass was planned long before
   the terrorist attacks of September 11, 2001, but they made the project
   a higher priority.

Powerlines leaving the power plant

   The switchyard of Hoover Dam powerstation is situated in the canyon. So
   the outgoing powerlines are installed on electricity pylons, which are
   built as inclined towers. (Please expand and add pictures)

Power distribution

   Hoover Dam Angel
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   Hoover Dam Angel

   The Bureau of Reclamation reports that the energy generated is
   allocated as follows:
                          Area                        Percentage
   Arizona                                               18.9527
   Nevada                                                23.3706
   Metropolitan Water District of Southern California    28.5393
   Burbank, CA                                            0.5876
   Glendale, CA                                           1.5874
   Pasadena, CA                                           1.3629
   Los Angeles, CA                                       15.4229
   Southern California Edison Co.                         5.5377
   Azusa, CA                                              0.1104
   Anaheim, CA                                            1.1487
   Banning, CA                                            0.0442
   Colton, CA                                             0.0884
   Riverside, CA                                          0.8615
   Vernon, CA                                             0.6185
   Boulder City, NV                                       1.7672

Statistics

   Downstream from Hoover Dam, showing the river, power stations, and
   power lines.
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   Downstream from Hoover Dam, showing the river, power stations, and
   power lines.
     * Construction period: April 20, 1931 – March 1, 1936
     * Construction cost: $49 million ($676 million adjusted for
       inflation)
     * Deaths attributed to construction: 96
     * Dam height: 726.4 ft ( 221.4 m), second highest dam in the United
       States.
     * Dam length: 1244 ft ( 379.2 m)
     * Dam thickness: 660 ft (200 m) at its base; 45 ft (15 m) thick at
       its crest.
     * Concrete: 4.36 million yd³ ( 3.33 million m³)
     * Electric Power produced by the water turbines: 2,080 megawatts
     * Fatalities during construction: 96+
     * Traffic across the dam: 13,000 to 16,000 people each day, according
       to the Federal Highway Administration
     * Lake Mead (full pool)
          + area: 157,900 acres (639 km²), backing up 110 miles (177 km)
            behind the dam.
          + volume: 28,537,000 acre feet (35.200 km³) at an elevation of
            1,221.4 feet (372.3 m) .
     * With 8 to 10 million visitors each year, including visitors to
       Hoover Dam but not all traffic across the dam, the Lake Mead
       National Recreation Area is the fifth busiest U.S. national park.

The naming controversy

   The dam, originally planned for a location in Boulder Canyon, was
   relocated to Black Canyon for better impoundment, but was still known
   as the Boulder Dam project. Work on the project started on July 7,
   1930. At the official beginning of the project on September 17, 1930,
   President Hoover's Secretary of the Interior Ray L. Wilbur, announced
   that the new dam on the Colorado River would be named Hoover Dam to
   honour the then President of the United States. Wilbur followed a
   long-standing tradition of naming important dams after the President
   who was in office when they were constructed, such as Wilson Dam and
   Coolidge Dam. Furthermore, Hoover was already campaigning for
   re-election in the face of the Depression and sought credit for
   creating jobs. A Congressional Act of February 14, 1931, made the name
   "Hoover Dam" official.

   In 1932, Hoover lost his bid for reelection to Franklin Delano
   Roosevelt. When Roosevelt took office on March 4, 1933, he brought
   Harold Ickes with him to replace Ray Lyman Wilbur as Secretary of the
   Interior. Ickes wasted no time removing Hoover’s name from the Boulder
   Canyon Project. On May 8, 1933, Ickes issued a memorandum to the Bureau
   of Reclamation, which was in charge of the dam, stating, "I have your
   reference to the text for the pamphlet descriptive of the Boulder
   Canyon Project for use at the Century of Progress Exposition. I would
   be glad if you will refer to the dam as 'Boulder Dam' in this pamphlet
   as well as in correspondence and other references to the dam as you may
   have occasion to make in the future."

   Ickes could not "officially" change the name of the dam, as that had
   been set by Congress, but the effect was the same: all references to
   "Hoover" Dam in official sources, as well as tourist and other
   promotional materials, vanished in favour of "Boulder" Dam.

   Roosevelt died in 1945 and Harold Ickes retired in 1946. On March 4,
   1947 California Congressman Jack Anderson submitted House Resolution
   140 to "restore" the name Hoover Dam. Anderson’s resolution passed the
   House on March 6; a companion resolution passed the Senate on April 23,
   and on April 30, 1947, President Harry S. Truman signed Public Law 43
   which read: "Resolved … that the name of Hoover Dam is hereby restored
   to the dam on the Colorado River in Black Canyon constructed under the
   authority of the Boulder Canyon Project Act … . Any law, regulation,
   document, or record of the United States in which such dam is
   designated or referred to under the name of Boulder Dam shall be held
   to refer to such dam under and by the name of Hoover Dam."

Image gallery

   The dam crosses the border between two time zones, the Pacific Time
   Zone the Mountain Time Zone

   From above down towards the Colorado River side

   View downstream from top of dam

   A panoramic view of Hoover Dam.

   The canyon downstream from Hoover Dam.

   Nevada-Arizona border at middle of Hoover dam.

   View downstream from top of dam

   View downstream from top of dam

   View upstream from top of dam

   Hoover Dam at Night

   Hoover Dam at Night

Trivia

   Aerial shot of Lake Mead and Hoover Dam showing the high-water mark of
   the 1983 flood season along the shore
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   Aerial shot of Lake Mead and Hoover Dam showing the high-water mark of
   the 1983 flood season along the shore
     * In the NBC miniseries, 10.5: Apocalypse, the dam was featured.
       Groundwater from underneath Lake Mead rose to its surface, causing
       Hoover Dam to overflow, and collapse, sending flash floods
       downstream of the Colorado River, and causing major flooding to
       towns along the Nevada/ Arizona and California/ Arizona borders.
     * The hardhat was invented, and first used, by the construction
       workers of the Hoover Dam. It was originally made of two baseball
       caps dipped in tar and allowed to harden.
     * The construction of the Hoover Dam project, controversies and Chief
       Engineer Frank Crowe's role were dramatised in a one-hour TV
       docu-drama, as part of the BBC's Seven Wonders of the Industrial
       World series in 2003 available on DVD and paperback.
     * The large spillway tunnels blasted into the Black Canyon walls for
       Hoover Dam have only been used twice in the history of the dam; the
       first was during a planned period in the second half of 1941 for
       testing the spillways, and the second one was for about six weeks
       during the summer of 1983 when a snow-melt flood in the Colorado
       River basin made use of the spillways necessary.
     * The 1983 high-water mark or "bathtub ring" is visible in many
       photos that show the shoreline of Lake Mead. Much of the
       vegetation, which was killed, has not recovered from the unusually
       high precipitation that the Western United States received in that
       1982-1983 season as a result of an El Niño event.
     * Usually all the flow of the Colorado River, other than that lost to
       evaporation in Lake Mead, passes through the water turbines of the
       Hoover Dam powerhouse.
     * The concrete is still curing, gaining in strength every day.
     * The dam is sung of in The Highwaymen's "Highwayman" song. It tells
       the story of a dam builder who fell in wet concrete during
       construction and died.
     * The first person to die in the construction of Hoover dam was J. G.
       Tierney -- a surveyor who drowned while looking for an ideal spot
       for the dam. His son, Patrick W. Tierney, was the last man to die
       working on the dam, 13 years to the day later (see Fatalities at
       Hoover Dam).
     * The two outer diversion tunnels had a large concrete plug inserted
       approximately halfway along their length. The two spillways of the
       dam drop sharply, and enter the outer diversion tunnels through
       their ceiling, after the concrete plugs. In effect the outer
       diversion tunnels have been cut in two, and the downstream half
       used as part of the spillway tunnels.
     * The two inner diversion tunnels had a large concrete plug inserted
       approximately halfway along their length. Their downstream half is
       now used as the main tunnel which carries water from the intake
       towers to the generators. Downstream from the generators, there is
       a second concrete plug in the inner diversion tunnels. They have
       effectively become a chamber which is used to transport water from
       the intake towers to the generators.

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