Hoover Dam began operations in 1936. It impounds one of the largest reservoirs (by volume) in the United States. Originally called “Boulder Dam”, it was renamed Hoover Dam after congress voted to make the name official in 1947.

Even today, 75 years after it was built, it remains one of the largest, most reliable hydroelectric generators in the US. Something like that can’t last forever, can it? Does the Hoover Dam have a set lifespan or expiration date?

3 Million Horses

Hoover Dam provides power to Nevada, Arizona and large swathes of California. In 2011, president Obama signed a bill extending the previous supply contracts to the year 2067. He also set aside 5% of its power to be made available for purchase by Native American tribes and electric cooperatives.

53.5% of its total output goes to California, with 15.4% of that number going to Los Angeles alone. Arizona uses 18.9% while 23.3% is allocated to Nevada.

So how much total power does Hoover Dam supply to its customers annually? A whopping 4.2 billion kWh of electricity every year. It achieves this through its efficient turbines which have a rated capacity of 2,998,000 horsepower. There are a total of 17 main turbines which were replaced and upgraded with more efficient and powerful units back in the late 80s. There are also 2 smaller turbines which exist to provide the dam itself with electricity.

Mollusks End The Power Hour

Without continual maintenance or a human presence, the dam would stop producing power after the hydroelectric system and/or turbines stopped functioning. Speculation by several engineers who work at the dam believe that this could take anywhere from a few months to a few years.

Several things can cause the system to malfunction, with the most likely candidate being the quagga mussel. It has no natural predators in North America and workers must routinely scrape them out of the pipes and grates they like to colonize.

With humans gone, their unchecked growth would cause blockage in the cooling pipes which would lead to overheating of the turbines. When the turbines overheat, the system automatically shuts down the offending turbine to prevent a catastrophic failure of the hydroelectric system. No turbines means no power.

Built To Last

The dam itself was built to last. It was built to be as tough as the canyon walls which surround it. A total of 3,250,000 cubic yards of concrete was poured to create the dam – it’s enough to build a monument 100 feet square and 2 1/2 miles high.

One common misconception is that the dam was built with a single, continuous concrete pour. Since concrete contracts & heats up as it cures, if it was all poured at once, it would have taken 125 years for the concrete to cool off. Such a long cure time would have also created a weaker dam, one highly susceptible to stress and microcracks.

Instead, the concrete was poured in separate sections which took only 2 years to complete. Rectangle shaped sections were marked off and concrete was poured into each, creating individual blocks. The separate blocks had their curing process sped up due to ice-cold water that was refrigerated then pumped in through embedded cooling pipes which helped the concrete cure evenly.

All Good Things…

Despite concrete’s tenacity, a lack of maintenance will eventually cause the dam to crumble. However, speculation puts the time at which this happens in the thousands of years, several reports put it at 10,000+ years. If humans were to vanish of the face of the planet, the Hoover Dam would be one of the last remaining visible and recognizable monuments of our species on the planet.

With the turbines non-functional, the Colorado River dries up as water no longer passes through the dam. The dam’s reservoir, Lake Mead, slowly rises until the water finds a way over, around, under or through the dam. Wind, water, and possibly earthquakes will take their toll and even the massive wall of concrete will wear down and erode, inevitably succumbing to the elements.

Fun Fact: Many pieces of unique art decorate the dam. One such piece at the base of the dam, set in a terrazzo floor, is an inlaid star chart designed by Oskar J.W. Hansen. The apparent magnitudes of stars on the chart are shown as they would appear to the naked eye at a distance of about 190 trillion miles from earth.

The planetary bodies are placed in a way that someone could calculate the precession of the Pole Star for the next 14,000 years accurately. It’s also accurate enough that future generations could look upon this chart and determine the exact date on which Hoover Dam was completed.





References:

Denton, Sally. “Hoover’s Promise: The Dam That Remade The American West”, American Heritage’s Invention & Technology

Bureau of Reclamation (2006). Reclamation: Managing Water in the West: Hoover Dam. US Department of the Interior.

“Hoover Dam”. National Historic Landmark summary listing. National Park Service.

Rhinehart, Julian (September 10, 2004). “The Grand Dam“. Bureau of Reclamation.

