Dams come in a variety of sizes and serve a number of purposes. Our nation’s dams provide essential benefits such as drinking water, irrigation, hydropower, flood control, and recreation. The public most commonly thinks of engineering marvels like the Hoover Dam in Nevada rather than the smaller structure that created the lake at the center of a planned community. No matter how large or small, dams have a powerful presence that frequently is overlooked until failure has occurred.
The safe operation and proper maintenance of dams is critical to sustaining the benefits, while mitigating the risk of a dam failure. Yet despite their importance, thousands of dams remain in need of rehabilitation to meet current design and safety standards. These structures are not only aging, but are subject to stricter criteria because of increased downstream development and advancing scientific knowledge predicting flooding, earthquakes, and dam failures.
Dams are classified based on their hazard potential, or anticipated consequences in the case of failure. The failure of a dam that is classified as high-hazard potential is anticipated to cause a loss of life. The number of high-hazard potential dams is growing rapidly; as of 2015, there are approximately 15,500 dams in the United States that are classified as high-hazard potential. This number has climbed from 10,213 high-hazard potential dams in 2005 and is anticipated to continue to climb as areas below dams continue to be developed. With population growth expected to slow, the U.S. has an opportunity to more methodically develop currently unpopulated areas to avoid placing homes and other structures below dams, thereby reducing the number of structures classified as “high-hazard potential.” Another 11,882 dams are currently labeled as significant-hazard potential, meaning a failure would not necessarily cause a loss of life, but could result in significant economic losses. While these figures climb, the increase has slowed because more dams are inspected on a more regular basis, allowing for the identification of deficiencies before they lead to a failure.
The average age of our nation’s dams is 56 years. By 2025, seven out of 10 dams in the United States will be over 50 years old. Fifty years ago dams were built with the best engineering and construction standards of the time. However, as the scientific and engineering data have improved, many dams are not expected to safely withstand current predictions regarding large floods and earthquakes. In addition, many of these dams were initially constructed using less-stringent design criteria for low-hazard potential dams due to the lack of development.
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