Hoover Dam

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Hoover Dam (Template:Coor dms) is a concrete gravity-arch dam in the Black Canyon of the Colorado River, on the border between Arizona and Nevada. The dam, located 48 kilometres (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. Hoover Dam was built by Six Companies, Inc., under Frank Crowe. Construction began in 1931 and was completed in 1936, over two years ahead of schedule. The dam is 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.

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. The contract to construct the dam was awarded to Six Companies Inc., a joint venture of Morrison-Knudsen Company of Boise, Idaho; Utah Construction Company of Ogden, Utah; Pacific Bridge Company of Portland, Oregon; Henry J. Kaiser & W. A. Bechtel Company of Oakland, California; McDonald & Kahn Ltd. of Los Angeles; and J. F. Shea Company of Portland, Oregon.

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. [1].

To divert the river's flow around the construction site, four tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were to be 56 feet (17 m) in diameter. Their combined length was nearly 16,000 feet (4880 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 mm) thick, reducing the finished tunnel diameter to 50 ft (15 m).

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.

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 unwatered, 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.

The first concrete was placed into the dam on June 6, 1933. Since no structure the magnitude of Boulder 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. 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. Each form also contained cooling coils of 1 inch (25 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.

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. The seventeen main turbines at this powerhouse generate 2,074 megawatts of hydroelectric power.

The dam and powerplant are operated by the United States Department of the Interior's Bureau of Reclamation.

In addition to its economic and engineering renown, Hoover Dam is accounted a masterpiece of Art Deco design.

Statistics

  • Construction period: April 20, 1931 - March 1, 1936
  • Construction cost: $49 million ($676 million adjusted for inflation)
  • Dam height: 726.4 ft (221.4 m), 2nd highest dam in the United States.
  • 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 )
  • Traffic across the dam: 13,000 to 16,000 people each day, according to the Federal Highway Administration
  • Lake Mead statistics
    • 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 5th 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 honor 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, and 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 reference to "Hoover" Dam vanished in favor of "Boulder" Dam. Official sources, as well as tourist and other promotional material now read 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

Template:Colorado River system

External links

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