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The USA’s Biggest Dams and Their Conservation Challenges

Most of the United States biggest dams are in the Western side of the country. This is due to the natural topography, with more elevation changes and steep river valleys. Our own Flaming Gorge Dam would come in at 15th on this list with a height of 502 feet. The top three are nearly 50% taller than that, with all of them weighing in at over 700ft.

Oroville Dam, California

Built on the Feather River, near the city of Oroville, this earthen embankment dam is 770 feet tall. It holds back Lake Oroville, one of the largest freshwater sources in the state containing over 4.3 trillion litres. This dam’s particular challenges for its future include the less than highly technical nature of its construction, and the blocking of fish migration routes from further up the river.

Oroville Dam, California
Oroville Dam, California

In 2017 an unusually rainy winter season in California caused the water level to rise over into the emergency spillway. Such was the force of this rare event that the emergency overflow route was badly damaged – to the point that 180,000 downstream residents had to be evacuated. Luckily, the headward erosion was not too severe and the floodwaters eventually receded. Efforts to ensure the situation won’t happen again are ongoing.

Hoover Dam, Arizona & Nevada

This archetypal arched concrete gravity dam is one of the most famous American landmarks and holds back the largest reservoir in the US (when full). Blocking off the Colorado River near Boulder, Arizona, it stands at an impressive 726 feet. Completed in 1936, over a hundred workers died during its construction. Today it provides drinking water and hydroelectric power to millions of people – including Sin City, Las Vegas itself. Its main challenges include its sheer size, large amounts of visitor numbers and a diminishing water supply as the populations of the surrounding area continue to rise. In fact, Hoover Dam nearly had to shut down power production in 2010 as water levels reached the minimum required for successful operation. A solution required five massive new wide-head turbines to be installed in 2012, in the first major addition the power plant since the 1980s.

Dworshak Dam, Idaho

Blocking off the Clearwater River, this dam is the largest straight-axis dam in the US and the Western Hemisphere more generally. This is because Hoover Dam, though higher, is an arched curve – not on a straight axis. It’s also the only dam on this list to be built directly by the US Army Engineer Corps, rather than a consortium of private companies hired by the government.

Dworshak Dam, Idaho
Dworshak Dam, Idaho

The Dworshak Dam’s biggest challenges involve structural upkeep and the disruption of fish migration. During construction in 1966, an entire fish hatchery was constructed a mile or so downriver from the site of the dam. Experts estimate that over three million baby fish are released into the river system each year from the Dworshak hatchery. The last time a big crack opened was a 70 foot one in 1980 – but authorities are constantly on the lookout for further signs of degradation in what is after all a 55-year-old structure.