Amazing structures – the Hoover Dam
Hoover Dam in the United States is one of the most pioneering achievements of engineering of all time. 90 years after construction began, the dam remains in use and is a key infrastructure project, supplying water and electricity to one of the driest regions of the US.
Where is the Hoover Dam?
Hoover Dam is situated on the border between Arizona and Nevada (the border is the Colorado River itself) in the US Southwest. The Dam is about 40 miles from Las Vegas.
When did construction start on the dam?
Work on the Dam began in March 1931, upon the orders of President Herbert Hoover, after whom the Dam was named.
When did the Hoover Dam open?
Hoover Dam became operational in March 1936.
A brief history of the Hoover Dam
As the population grew across the US Southwest in the late 19th and early 20th centuries, much talk centred on the 1,450-mile-long Colorado River and how it could be used to help the development of towns, cities and industries. There were also fears about the flood risk the river could pose. A ‘Bureau of Reclamation’ considered various plans and identified the site of Black Canyon as the most suitable for a dam.
In an unprecedented move, seven US states came together (California, Nevada, Arizona, Utah, New Mexico, Colorado and Wyoming) to develop the dam project during the 1920s. It was authorised by US President Coolidge in 1928.
How did they build the Hoover Dam?
The sheer scale of the natural challenges faced by the Hoover Dam engineers is astonishing. The Black Canyon walls are 726 feet high; the dam had to fill a gap nearly 1,250 feet wide. The Colorado River needed to be re-routed to clear the riverbed, and the outer rockface of the canyon had to be removed and smoothed by manual labour.
But this was also one of the hottest, most inhospitable parts of the US. Summer temperatures in Arizona and Nevada can reach 45°C or higher. Construction also took place during the Great Depression, when many thousands of unemployed Americans flocked to the site looking for work. All of these factors were part of what makes the building of the Hoover Dam such an incredible story.
Design features
Hoover Dam is a gravity arch dam – a curved structure, forcing water to the edges of the canyon where pressure is lower. The dam is considerably thicker at its bottom than at the top, again reducing water pressure and increasing the dam’s stability. The dam was designed to be able to bend safely, without the concrete developing cracks.
Planning & preparation
It took two years to complete the preliminary stages of the construction project. The first stage was the draining and re-routing of the Colorado River to clear the dam basin. This was achieved using diversion tunnels and cofferdams, which would also be used to pump water back in after the dam was built.
Then the canyon had to be made a stable surface for the dam to be built into. The opposing vertical slopes of the canyon were composed of weathered uneven rock, which would not have been strong enough to hold the dam, so workers abseiled down the sides of the canyon, planting dynamite and using jackhammers to smooth out the exposed rock. People came from miles around to watch the abseilers do their death-defying shifts.
The construction process
Timeline & milestones
- March 1931 - Construction began
- June 1933 – First concrete poured
- Sept 1935 – Dedication by Franklin D. Roosevelt
- March 1936 – Dam handed over to federal government
Construction methods & materials
When the dam was opened it was the largest concrete structure in the world. In total 3,250,000 cubic yards of concrete were used – enough for a two-lane road stretching from the West to the East coast of the US. Jackhammers and dynamite were the main tools used to excavate the rock. It was incredibly dangerous work. But employment was scarce and there was no shortage of men lining up to do it.
Another interesting aspect of the Hoover Dam story was that it helped to invent hard hats. The construction workers dipped their cloth hats in tar and let them harden in the baking sun. The hats offered some protection from falling debris and by the end of the project they were being mass-produced.
Challenges faced during construction
The concrete could not be applied in one continuous pour – if it had it would have generated too much heat and would have taken 125 years to set! A solution was found. The dam is built of thousands of interlocking blocks up to 15 metres square, each with pipes running through them. Concrete was poured into each block, and cold water ran through the pipes. The blocks cooled and set quickly enough for the dam to be constructed two years ahead of schedule. The technique was so successful that, remarkably, no cracks emerged in the concrete nearly 90 years after the dam was built. Testing in 1995 showed the concrete had instead gained in strength.
Housing the workers was a huge challenge. At its peak, the site employed over 5,000 men, but many more came with the hope of escaping the Great Depression. The plan had always been to build a new town to house the workers – but Boulder City, as it is still known, was not ready when construction started in March 1931. Workers and their families lived in appalling conditions in a shanty town of tents called ‘Ragtown’, and drank and gambled in what was then the relatively small Nevada town of Las Vegas.
How much did the Hoover Dam cost?
It cost around $49 million ($760 million in today’s money) to build the Dam. The electricity generated by the hydroelectric power plant at the Dam effectively paid back the cost of construction by 1987.
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Though technologies, building techniques and safety procedures have changed, Hoover Dam is very much one of the first modern engineering and construction projects. Dams like it are still being built today, and working on projects like it can be very rewarding, encompassing almost every job role in the construction industry. These are just a few:
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