The Engineering Behind the Hoover Dam

On the border between Nevada and Arizona lies the Hoover Dam, constructed between 1931 and 1936.

Sitting between its natural abutments – the parts of the canyon between which the dam is constructed – the Hoover Dam is made from stacked, interlocking sections of concrete in a structure that stands 726 feet tall and is 660 feet thick at its base. This made Hoover Dam the largest manmade structure to have ever been built at this time.

The Hoover Dam is an ‘arch-gravity’ dam – a hybrid between two types of dam, the arch dam and the gravity dam. A gravity dam relies on its huge weight to cope with the force of the water, while arch dams have a curved design – the pressure of the water against the arch causes the arch to straighten a little against its abutments, which provides strength to the dam. An arch-gravity dam combines these features. Hoover Dam is made from a whopping 6.6 million metric tons of concrete and is also curved towards its abutments, making the ‘arch’ that directs much of the water pressure towards the hard canyon walls, which are formed from strong volcanic rock.

This strength is needed to hold back the 10-trillion gallon reservoir Lake Mead – the largest reservoir in the U.S. when full.

One of the most important functions of Hoover Dam is to prevent floods. Though the reservoir is enormous, a reinforced concrete spillway at each side of the canyon wall was built to ensure water never spilled over the top of the dam. These spillways were formed by drilling and blasting holes in the canyon rock with dynamite, before concrete was laid on a foundation of volcanic rock to create these structures. When the water in the reservoir reaches a certain level, it falls over into the spillways, where it is directed into the river below the dam.

As well as stopping floods and providing water to farms in the surrounding areas, one of the most important functions of Hoover Dam is to produce hydroelectric power – which it does for around 8 million people in Arizona, Nevada and even California.

To achieve this, a U-shaped power plant was built with two ‘wings’ or ‘arms’ containing giant electric generators, with one wing built on each side of the canyon wall. There are nine giant electric generators in the Arizona wing and eight on the Nevada wing.

To allow the water to be converted to electricity, four tall towers called ‘intake towers’ were built in the reservoir impounded by the Hoover Dam. Made from concrete and steel, two of these towers can be seen at each side of Lake Mead.

Water from the reservoir enters these towers through two cylindrical gates 32 feet in diameter and 11 feet high and which are protected by trash racks – railings to prevent objects in the water from entering the penstocks, the large steel pipes which direct water away from the towers.

Water is directed through the penstock system and passed over turbines. As the water passes over the turbines, the turbines rotate and produce mechanical energy that is transformed by the electrical generators into electricity, providing millions of Americans with hydrostatic electricity.