Boulder Dam Is Completed Summary

  • Last updated on November 10, 2022

Completion of Boulder Dam provided irrigation, municipal water, flood control, and abundant power, but it also catalyzed great environmental and economic change.

Summary of Event

Boulder Dam (also called Hoover Dam after 1947) was officially accepted by Secretary of the Interior Harold Ickes on March 11, 1936. On completion, the dam was the world’s highest and largest, rising 727 feet above bedrock and containing more than 3 million cubic yards of concrete. The Grand Coulee Dam, completed in 1942, surpassed it with more than 10 million cubic yards of concrete, and the Mauvoisin Dam, completed in Switzerland in 1958, was the first higher dam at a height of 777 feet. Lake Mead was formed by Boulder Dam; with a capacity of more than 31 million acre-feet of water, it was the world’s largest reservoir until 1959, when the Kariba Dam on the Zambia-Zimbabwe boundary created a reservoir of 130 million acre-feet capacity. Boulder Dam and Lake Mead, however, remain among the largest structures of their kind. [kw]Boulder Dam Is Completed (Mar. 11, 1936) [kw]Dam Is Completed, Boulder (Mar. 11, 1936) Boulder Dam Hoover Dam Engineering;dams Dams;Boulder [g]United States;Mar. 11, 1936: Boulder Dam Is Completed[09180] [c]Environmental issues;Mar. 11, 1936: Boulder Dam Is Completed[09180] [c]Natural resources;Mar. 11, 1936: Boulder Dam Is Completed[09180] [c]Engineering;Mar. 11, 1936: Boulder Dam Is Completed[09180] [c]Energy;Mar. 11, 1936: Boulder Dam Is Completed[09180] Kaiser, Henry J. Mead, Elwood Wilbur, Ray Lyman Hoover, Herbert [p]Hoover, Herbert;Boulder Dam Swing, Philip D. Wozencraft, Oliver M. Crowe, Frank Davis, Arthur Powell Young, Walker

The Boulder Dam project had its roots in Oliver M. Wozencraft’s efforts to promote diversion of Colorado River water to irrigate the Imperial Valley of California. In 1859, at Wozencraft’s instigation, the California legislature passed a bill petitioning Congress to cede the Imperial Valley to the state for reclamation purposes. Wozencraft’s desert-land bill finally was introduced in Congress in 1862 but failed to pass. Private construction of irrigation works began in 1898, and the first water was diverted in 1901. Severe floods in 1905 and 1906 broke through the levees and canals, bringing Colorado River water to the Salton Depression and creating the Salton Sea. It took two years to bring the flood under control, and the strong possibility remained that the river could break through again. A flood would inundate more than one million acres of irrigated farms. Erosion of the channel also threatened to dry out additional irrigated lands at Yuma, Arizona, and farmland to the north. Furthermore, the 1905-1906 flood and subsequent floods exceeded the financial capacity of private companies and irrigation districts to maintain irrigation systems in the valley. The inability of private organizations to cope with the flood threat and the advent of proposed private hydroelectric power schemes resulted in appeals for governmental intervention.

Conflicting claims by the states of the Colorado basin for river water and the perceived need to regulate public and private power caused Congress, on August 19, 1921, to authorize the states of the Colorado River drainage basin to enter into a compact dividing the basin’s waters. The Colorado River Commission, which was composed of representatives of the states as well as the secretary of commerce, was appointed by the president and states. At the commission’s first meeting, on January 26, 1922, Herbert Hoover, the U.S. secretary of commerce, was elected chairman. After prolonged controversy, the Colorado River Compact Colorado River Compact (1922) was signed by the commission on November 24, 1922, opening the way for unified development of the Colorado River basin. The means by which that development was achieved, however, remained controversial.

The Colorado River Compact divided the basin into a lower basin comprising Arizona, California, and Nevada and an upper basin within Utah, New Mexico, Colorado, and Wyoming. Both basins were allocated 7.5 million acre-feet of water and the right to draw an additional one million acre-feet of unallocated water for beneficial consumption if additional water was available. Division of water within the upper and lower basins, however, was not specified, and conflict between Arizona and California remained an obstacle. The water allocated was designated primarily for domestic and agricultural purposes, secondarily for power generation, and thirdly for navigation. Much later, Mexico was allocated 1.5 million acre-feet from the surplus waters. If there was insufficient surplus water to supply the Mexicans, the lower and upper basins were required to surrender equal amounts to fulfill the Mexican quota. Arizona and the upper-basin states immediately objected, because California had already appropriated all, or nearly all, of its share of the water and was prepared to take more. In contrast, the upper-basin states lacked the dams and reservoirs needed for storage and diversion of their share of the water. In addition, conflicts over the role of government and private enterprise in producing and selling electrical power delayed construction.

After prolonged political maneuvering, the fourth Swing-Johnson bill (named for its primary author, Congressman Philip D. Swing of California), which authorized the Boulder Canyon Project, passed Congress on December 19, 1928. Three previous versions failed to pass in 1922, 1923, and 1925. Under the terms of the act, also known as the Boulder Canyon Project Act, Boulder Canyon Project Act (1928) a high dam and reservoir were to be constructed at either Boulder or Black Canyon in order to control floods, improve navigation, regulate the flow of the Colorado River, store water for reclamation and other beneficial purposes exclusively within the United States, and generate electrical energy. Construction of the Imperial Dam and All-American Canal, which were designed to divert water to the Imperial Valley by means of works entirely within the United States, also was authorized in the bill.

Construction of the high dam commenced on May 16, 1931. Because of engineering considerations, the dam was built in Black Canyon instead of in Boulder Canyon. A town, a railroad, a highway, and power lines were built to allow construction to proceed in the previously isolated, uninhabited area. Four diversion tunnels were driven around the site, and a cofferdam was erected to keep the river out of the dam site. The diversion tunnels became operable in March, 1931, and the upper cofferdam was completed in March, 1933. On June 6, 1933, the first concrete was poured for the dam after the rock abutments had been stripped and the valley floor excavated to bedrock. On March 23, the main body of the dam was completed to crest elevation. The large volume of concrete required cooling to dissipate the heat of curing and to avoid cracking and deforming the dam. For this purpose, refrigerant piping was buried in the concrete, and a substantial refrigeration plant was built to supply internal cold-water circulation. This technique, invented for Boulder Dam’s construction, was later used for building other massive concrete structures.





The dam began regulating Colorado River flow on February 1, 1935. It was dedicated on September 30, 1935, and was accepted by Secretary of the Interior Harold Ickes on March 1, 1936, two years and two months ahead of schedule, at a cost of $51,950,000—essentially the price at which it had been bid. By June, 1937, the power plant was in routine operation, although not all the contemplated turbines and generators were installed until decades later. The dam was renamed Hoover Dam in 1947 to honor Herbert Hoover, who as secretary of commerce and as president of the United States played a large role in the dam’s construction.


Boulder Dam fulfilled all the purposes for which it was built. Irrigation water was supplied to the Imperial Valley and riverine lands below the dam. Water stored in the reservoir became available to maintain irrigation during droughts. Flooding on the Lower Colorado River occurred only once after completion of the dam, and the great flood of 1953 would have been far more severe without storage of much of the waters in Lake Mead. An installed capacity of 4.33 million kilowatt-hours of electric power was expected upon installation of all planned generators. Additional benefits of the dam’s construction included temporary stimulation of the economy in the midst of the Great Depression and creation of a major recreational resource. This resource, the Lake Mead National Recreation Area, Lake Mead National Recreation Area preserved a large area of desert environment.

Boulder Dam was the first very large modern dam, and it initiated worldwide expansion of large-scale hydroelectric and irrigation-dam construction. The Tennessee Valley Authority, the Columbia basin system, and the Pick-Slogan program in the Missouri basin were developed in part because of the momentum generated by completion of Boulder Dam. The federal government constructed more than one thousand dams between 1930 and 1980. Construction of the Parker Dam and the Colorado River Aqueduct began immediately after completion of Boulder Dam. Aqueducts to service San Diego and the Coachella Valley were built somewhat later and met California’s primary objectives for the Boulder Canyon Project. Efforts to secure use of the upper basin and Arizona’s share of the water, however, were unsuccessful.

The Colorado River Storage Project, which was approved by Congress in 1956, authorized construction of ten dams in the upper Colorado River basin. These dams were to store 48.5 million acre-feet of water and to ensure delivery of the upper basin’s share of water as stated in the Colorado River Compact. Glen Canyon Dam, completed in 1966, was the largest of those actually built. The Central Arizona Project, authorized in the Colorado River Basin Project Act, signed on September 30, 1968, finally delivered Arizona’s share of water allocated under the Colorado River Compact. The Colorado River Basin Act also provided for a domestic water aqueduct to Las Vegas, authorized several upper-basin dams and projects, and assumed responsibility for delivering acceptable water to Mexico.

Although the completed works in the Colorado basin are adequate to deliver the water allocated to the states of the basin and Mexico, most people believe that the river does not supply enough water to meet the quotas. The estimated average annual flow, on which the allocations were based, was determined by available flow rate measurements. These measurements, however, were made during a wetter-than-average climatic cycle. As a consequence, virtually no water reaches the Gulf of California. In addition, irrigation water leaches salts from the soil and returns saline water to the river. This process, as well as the natural increase in salinity as the river crosses the Colorado Plateau and the desert, so degraded the river water at the Mexican boundary that it became unfit for irrigation. Crop damage in Mexico provoked protests from the Mexican government, and these protests culminated in 1973 with a threat to bring the matter before the World Court. This protest has been somewhat quelled by the authorized construction of a $300 million desalination plant to treat water crossing the border and additional salinity-control projects upstream. Water flowing downstream to the Gulf of California is even more highly saline and has greatly altered wetlands on the Colorado River delta. Reduction in flow also has led to saltwater incursion on the delta.

Boulder Dam and Lake Mead remove all sediment from the Colorado River. As a consequence, the clear water below the dam erodes the bed and banks of the river. Also, the delta and the floodplain no longer receive sediment.

Water delivered by the Los Angeles and San Diego aqueducts permitted and stimulated the large population increase in Southern California. Irrigation water was ensured for the Imperial Valley and the districts along the Colorado River. Power from Hoover Dam serviced the pumps on the aqueducts and met a large part of the increased power demands during World War II. A magnesium reduction works at Henderson, Nevada, was the principal source of magnesium for the war effort. Inexpensive power also was sent to the zinc mines at Pioche, Nevada.

The dam’s name has been subject to partisan political conflict and has been a source of confusion. The Democratic Swing-Johnson bills authorizing the dam referred to the Boulder Canyon Project and referred to the dam as Boulder Dam. On “driving the silver spike” on the branch line to the site, Ray Lyman Wilbur, Herbert Hoover’s Republican secretary of the interior, named the dam Hoover Dam, and this name subsequently was used in congressional bills and appropriations. In May, 1933, the new Democratic secretary of commerce, Harold Ickes, changed the name to Boulder Dam. In 1947, the first Congress elected with a Republican majority since 1932 passed a bill restoring the name Hoover Dam. Democratic President Harry S. Truman signed the bill. This ended the partisan series of name changes, but both names remain in common use. Boulder Dam Hoover Dam Engineering;dams Dams;Boulder

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Berkman, Richard L., and W. Kip Viscusi. Damming the West. New York: Grossman, 1973. Excellent volume about the process of damming rivers in the American West. Places the construction of Boulder Dam into a larger context and underscores its catalytic role.
  • citation-type="booksimple"

    xlink:type="simple">Dunar, Andrew J., and Dennis McBride. Building Hoover Dam: An Oral History of the Great Depression. Reno: University of Nevada Press, 2001. A people’s history of the dam’s construction that focuses on the day-to-day realities experienced by the workers.
  • citation-type="booksimple"

    xlink:type="simple">Hoover, H. C. The Memoirs of Herbert Hoover, the Cabinet, and the Presidency, 1920-1933. New York: Macmillan, 1952. Hoover’s own account of his actions, motives, and beliefs regarding the Boulder Canyon Project. Emphasizes his role in the Colorado River Commission and his work to clear the way for the project. Also relates details about the naming and renaming of the dam and about Hoover’s exclusion from the dedication ceremonies.
  • citation-type="booksimple"

    xlink:type="simple">Kleinsorge, Paul Lincoln. The Boulder Canyon Project: Historical and Economic Aspects. Stanford, Calif.: Stanford University Press, 1940. Provides excellent coverage of the legislative battle over the Boulder Canyon Project Act, or Swing-Johnson bill. Addresses how the legislative process works and accurately describes the underside of that process.
  • citation-type="booksimple"

    xlink:type="simple">_______. The Boulder Dam Project. Stanford, Calif.: Stanford University Press, 1941. Describes the Colorado River and the history of navigation, agriculture, flood control, and power development on the lower river. Reviews political action leading to construction of the dam and the financing and construction of the dam. Includes an economic evaluation of the project. Readable and comprehensive through 1940.
  • citation-type="booksimple"

    xlink:type="simple">McBride, Dennis. In the Beginning: A History of Boulder City, Nevada. Boulder City, Nev.: Boulder City Chamber of Commerce, 1981. Discusses the people involved in the project, although in a somewhat romanticized manner. Gives a feeling that through all the trials and tribulations, a sense of community was established. For a wide audience.
  • citation-type="booksimple"

    xlink:type="simple">Mann, Elizabeth, and Alan Witschonke. The Hoover Dam: The Story of Tough Times, Tough People, and the Taming of a Wild River. New York: Mikaya Press, 2001. A very readable account; written for high school students. Includes sidebars with first-person narratives. Fully illustrated.
  • citation-type="booksimple"

    xlink:type="simple">Moeller, B. S. Phil Swing and the Boulder Dam. Berkeley: University of California Press, 1971. Sympathetic political biography describes Swing’s dedication to furthering Imperial Valley irrigation. Minimizes Hoover’s contributions to the project. Readable and well documented.
  • citation-type="booksimple"

    xlink:type="simple">Reisner, Marc. Cadillac Desert. New York: Viking, 1986. Best seller about water policy in the western United States concludes that water is being overused, that water projects are largely uneconomical, and that desertification awaits. Describes and evaluates the entire Colorado River project.
  • citation-type="booksimple"

    xlink:type="simple">Stevens, Joseph E. Hoover Dam: An American Adventure. Norman: University of Oklahoma Press, 1988. Superb resource on the people who built the dam. Presents an especially strong account of the technical aspects of the construction, but pays little attention to the environmental impacts.
  • citation-type="booksimple"

    xlink:type="simple">Watkins, T. H., et al. The Grand Colorado: The Story of a River and Its Canyons. Palo Alto, Calif.: American West, 1969. The Colorado River is one of the great and majestic rivers in the United States. This volume captures the spirit of that river as it passes through some of the most hostile but beautiful areas if the country.
  • citation-type="booksimple"

    xlink:type="simple">Woodbury, D. J. The Colorado Conquest. New York: Dodd, Mead, 1941. Fictionalized account of events leading to construction of Hoover Dam and the All- American Canal. Asserts that the actions and statements of the historical figures portrayed are factual and that the fictional characters are composites of individuals the author knew as a resident of Brawley, California. Very readable.

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Categories: History