Residual soils form from weathered rocks and can be
found in many parts of the world with different characteristics and appearance
based on the type of parent rock they have formed of. This large range of
difference in residual soils leads to variety of studies that focus on
different aspects of this type of soil and therefore in the
Bureau director Arthur Powell Davis in 1922 outlined a plan before
Congress for a multipurpose dam in Black Canyon, located on the Arizona-Nevada border.
Named the Boulder Canyon project, after the original proposed site, the dam
would not only control flooding and irrigation, it would generate and sell
hydroelectric power to recoup its costs. Still, the proposed $165 price tag
concerned some lawmakers, while representatives of six of the seven states in
the river drainage area—Colorado, Wyoming, Utah, New Mexico, Arizona and
Nevada —worried that the water would primarily go to California.
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
didn’t become official until 1947.
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.
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.
Source: http://www.history.com/topics/hoover-dam
