The Construction of the Hoover Dam (25 Photos)
Hoover Dam is as tall as a 60-story building. It was the highest dam in the world when it was completed in 1935. Its base is as thick as two football fields are long. Each spillway, designed to let floodwaters pass without harming the dam itself, can handle the volume of water that flows over Niagara Falls. The amount of concrete used in building it was enough to pave a road stretching from San Francisco to New York City.
Although the dam would take only five years to build, its construction was nearly 30 years in the making. Arthur Powell Davis, an engineer from the Bureau of Reclamation, originally had his vision for the Hoover Dam back in 1902, and his engineering report on the topic became the guiding document when plans were finally made to begin the dam in 1922.
Hoover Dam was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt.
An inspection party near the proposed site of the dam in the Black Canyon on the Colorado River. 1928.
Four tons of dynamite are detonated in the canyon in the early stages of construction. May 12, 1933.
Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it. 1933.
To protect the construction site from the Colorado River and to facilitate the river’s diversion, two cofferdams were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted. 1933.
The cleared, underlying rock foundation of the dam site was reinforced with grout, called a grout curtain. Holes were driven into the walls and base of the canyon, as deep as 150 feet (46 m) into the rock, and any cavities encountered were to be filled with grout. This was done to stabilize the rock. 1933.
“High scalers” use jackhammers to shave loose rock off the walls of Black Canyon. 1935.
“High scalers” rappel down the canyon wall. 1934.
The concrete foundation of the dam is poured into separate blocks called “lifts”. September 11, 1933.
Since concrete heats and contracts as it cures, the potential for uneven cooling and contraction of the concrete posed a serious problem. Bureau of Reclamation engineers calculated that if the dam was built in a single continuous pour, the concrete would take 125 years to cool, and the resulting stresses would cause the dam to crack and crumble. Instead, the ground where the dam would rise was marked with rectangles, and concrete blocks in columns were poured, some as large as 50 ft square (15 m) and 5 feet (1.5 m) high.
Herbert Hoover, the 31st president of the United States and a committed conservationist, played a crucial role in making Davis’ vision a reality. As secretary of commerce in 1921, Hoover devoted himself to the erection of a high dam in Boulder Canyon, Colorado. The dam would provide essential flood control, which would prevent damage to downstream farming communities that suffered each year when snow from the Rocky Mountains melted and joined the Colorado River. Further, the dam would allow the expansion of irrigated farming in the desert, and would provide a dependable supply of water for Los Angeles and other southern California communities. In 1929, Hoover, now president, signed the Colorado River Compact into law, claiming it was “the most extensive action ever taken by a group of states under the provisions of the Constitution permitting compacts between states”.