The fourth part in this series is devoted to fete of great civil engineering in the 20th century.
I visited Hoover Dam in 2015 and was totally in awe of the immensity of the project.
Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt.
At the turn of the 20th century, farmers sought to divert the Colorado River to budding Southwestern communities via a series of canals. When the Colorado broke through the canals in 1905, creating the inland Salton Sea, the job of controlling the raging river fell to the U.S. Bureau of Reclamation.
Secretary of Commerce Herbert Hoover brokered the 1922 Colorado River Compact to divide the water proportionally among the seven states, but the legal wrangling continued until outgoing President Calvin Coolidge authorized the Boulder Canyon Project in December 1928. In honor of the new president’s contributions, Secretary of the Interior Ray L. Wilbur announced the structure would be called Hoover Dam at a 1930 dedication ceremony, though the name did not become official until 1947.
The U.S. Bureau of Reclamation devised plans for the Hoover Dam on the Arizona-Nevada border to tame the Colorado River and provide water and hydroelectric power for the developing Southwest.
As the Great Depression unfolded, hopeful laborers descended on Las Vegas and set up camp in the surrounding desert for the chance to work on the project. Those who were hired eventually moved to Boulder City, a community specifically built six miles from the work site to house its employees.
Meanwhile, the U.S. government set about finding a contractor to build the proposed 60-story arch dam. The contract was awarded in March 1931 to Six Companies, a group of construction firms that had pooled its resources to meet the steep $5 million performance bond.
The first difficult step of construction involved blasting the canyon walls to create four diversion tunnels for the water. Facing strict time deadlines, workers toiled in 140-degree tunnels choked with carbon monoxide and dust, conditions that prompted a six-day strike in August 1931. When two of the tunnels were complete, the excavated rock was used to form a temporary coffer dam that successfully rechanneled the river’s path in November 1932.
Construction within the strict timeframe proved an immense challenge, as the crew bored into carbon monoxide-choked tunnels and dangled from heights of 800 feet to clear canyon walls. The largest dam in the world at the time of its completion in 1935, this National Historic Landmark stores enough water in Lake Mead to irrigate 2 million acres and serves as a popular tourist destination.
The second step of involved the clearing of the walls that would contain the dam. Suspended from heights of up to 800 feet above the canyon floor, high scalers wielded 44-pound jackhammers and metal poles to knock loose material, a treacherous task that resulted in casualties from falling workers, equipment, and rocks.
Meanwhile, the dried riverbed allowed for construction to begin on the powerplant, four intake towers and the dam itself. Cement was mixed onsite and hoisted across the canyon on one of five 20-ton cableways, a fresh bucket capable of reaching the crews below every 78 seconds. Offsetting the heat generated by cooling concrete, nearly 600 miles of pipe loops were embedded to circulate water through the poured blocks, with workers continually spraying the concrete to keep it moist.
As the dam rose, block by block, from the canyon floor, the visual renderings of architect Gordon Kaufmann took form. Electing to emphasize the imposing mass of the structure, Kaufmann kept the smooth, curved face free of adornment. The powerplant was given a futuristic touch with horizontal aluminum fins for windows, while its interior was designed to pay homage to Native American cultures.
With the body of water that would become Lake Mead already beginning to swell behind the dam, the final block of concrete was poured and topped off at 726 feet above the canyon floor in 1935. On September 30, a crowd of 20,000 people watched President Franklin Roosevelt commemorate the magnificent structure’s completion. Approximately 5 million barrels of cement and 45 million pounds of reinforcement steel had gone into what was then the tallest dam in the world, its 6.6 million tons of concrete enough to pave a road from San Francisco to New York City. Altogether, some 21,000 workers contributed to its construction.
Hoover Dam fulfilled the goal of disseminating the one-wild Colorado River through the parched Southwest landscape, fueling the development of such major cities as Los Angeles, Las Vegas and Phoenix. Capable of irrigating 2 million acres, its 17 turbines generate enough electricity to power 1.3 million homes. The dam was designated a National Historic Landmark in 1985 and one of America’s Seven Modern Civil Engineering Wonders in 1994. It receives some 7 million visitors annually, while Lake Mead, the world’s largest reservoir, hosts another 10 million as a popular recreation area.
Construction started: 1931.
Height: 221 m
Architects: Henry J. Kaiser, Gordon Kaufmann
Area: 89 ha
Opened: 1 March 1936
Architecture firm: Six Companies, Inc.