Nevada and Arizona. Icon of Engineering: Inside Hoover Dam
Hoover Dam is a wonder of engineering and human determination. Although no longer among the world’s tallest dams, Hoover remains an impressive example of Depression-era design and construction. The dam site is a popular tourist site that has been featured in movies such as Superman (1978), National Lampoon’s Vegas Vacation (1997), and San Andreas (2015). Hoover Dam is located within the Colorado River’s Black Canyon and along the border between Nevada and Arizona. Just 55 kilometers from Las Vegas, the dam is responsible for creating Lake Mead, the largest reservoir in the U.S. Constructed for irrigation, to control floods, and for generating hydroelectric power, the dam was built between 1931 and 1936. More than 21,000 workers were involved in the project including a hundred who died during construction. Nearly 2.6 million cubic meters of concrete were used in the dam and another 850,000 for building the powerplant and support structures. According to the U.S. Bureau of Reclamation, concrete used in the dam’s construction could pave a road from San Francisco to New York City.
Project architects also took measures to make the dam visually striking. For example, elements of Art Deco were used in the design of turrets on the reservoir side. Architects also employed Native American motifs inspired by Pueblo and Navajo designs to depict clouds, water, and animals on walkways and other surfaces. For the Depression years, the dam was an enormous financial undertaking. The total project cost was $49 million dollars (about $1.1 billion today). President Franklin Roosevelt attended the dam’s dedication in September 1935. At its completion, Hoover Dam was the largest hydroelectric power generating facility in the world (today, that distinction is held by China’s Three Gorges Dam).
We parked in a covered garage on the Nevada side of the dam that was directly below transmission cables suspended between tilted steel towers. From there, we followed a pathway to the visitor center and nearby dam overlooks. To our right we could see four large towers rising from Lake Mead. It’s possible to see the high-water mark where the rocky slope changes from water-bleached white to dark gray. At its maximum capacity, the reservoir holds enough water to cover the state of Connecticut to a depth of three meters. Below us, we could see the dam’s enormous U-shaped concrete face, 379 meters wide and 221 meters tall. At its base is the power generating house. To make the generator house bombproof it was built with a 1.1-meter layer of concrete topped with sand and tar.
The dam has other safeguards such as diversion tunnels and jet-flow gates on either side of the power generating house that can be used to release water in an emergency. It is also protected by two spillways. Just downstream of the dam we could see the Mike O'Callaghan - Pat Tillman Memorial Bridge under construction. Measuring just over 330 meters in length, the bridge is the second highest (274m) in the U.S. and has the tallest concrete arch in the Western Hemisphere. Built so that vehicles would no longer cross the dam, the bridge opened in October 2010.
Operated by the U.S. Bureau of Reclamation, the dam has been open for tours since 1937. On average, more than a million people tour the dam each year. We purchased tickets for the 45-minute guided tour of the dam and powerhouse. Our tour group assembled near a brass and marble elevator that took us 152 meters downward to base level. The doors opened to reveal a dimly lit passageway carved from rock that transitions to a finished tunnel lined with white tile. At the end of the passageway was a balcony overlooking the generator room. Inside are 17 turbines, eight on the Nevada side and nine on the Arizona side. Before reaching the turbines, water from Lake Mead enters intake towers and then penstocks that gradually narrow to create a head water pressure of 180 meters. The entire flow of the Colorado River (equivalent to 15 swimming pools per second) passes through the penstocks before coming in contact with fins that spin the turbines.
From our vantage point we could see and hear the generators at work. Together they create 2,080 megawatts of electricity, enough to power a city of 1.3 million people. About half of energy generated at Hoover Dam is used by the Metropolitan Water District of Southern California and other California power consumers. The remainder goes to consumers in Nevada and Arizona. Before departing we walked through a ventilation tunnel that terminates at a louvered opening with downstream views of the Colorado River. In a few places we were able to see other passageways protected by locked gates.
