DAMSClimate Change Is Increasing Stress on Thousands of Aging Dams Across the U.S.
There are more than 91,000 dams across the U.S., in all 50 states, with diverse designs and purposes. The average dam age is 57 years, and more than 8,000 dams are over 90 years old. The most recent report card of the American Society of Civil Engineers estimates that 70% of U.S. dams will be more than 50 years old by 2030. Overall, the report gave U.S. dams a “D” grade and estimates that more than 2,300 are high hazard dams which could cause loss of life or serious property damage if they fail.
Heavy rainfall generated widespread flooding. in the Upper Midwest in late June 2024, putting at least one aging dam at risk. In southern Minnesota, the Blue Earth River cut a path around the Rapidan Dam in Rapidan Township, about 15 miles south of Mankato, on June 24, putting the structure at imminent risk of failing. Officials warned local residents that if the dam burst, the river could rise by 2 feet, but said that evacuations were not needed.
This event comes a year after flooding in Vermont collapsed at least one dam and threatened others. Hiba Baroud, associate professor and associate chair in the department of civil and environmental engineering at Vanderbilt University, explains how flooding stresses dams in a changing climate.
How Serious Is the Risk When Water Flows Over or Around a Dam?
These conditions can result in erosion, which subsequently could lead to a dam breach or failure and a sudden, uncontrolled release of impounded water.
The risk reflects the combined effect of a hazardous event, such as heavy rainfall, and the vulnerability of the dam. A vulnerable dam could be old, poorly maintained or not have enough spillway capacity to safely release water from the dam.
A dam’s design can affect its ability to withstand overtopping and resist failure. For example, concrete dams can typically better withstand certain levels of overtopping compared to soil embankment dams.
Overtopping accounts for 34% of all dam failures. How long water flows over a dam and the volume of water that flows over it are important factors in determining the likelihood that a dam will fail.
The consequences depend on several factors, such as the purpose of the dam, its size and its location. If a dam is designed for flood protection and is surrounded by homes, businesses or critical infrastructure, a large uncontrolled release of water could be catastrophic. Dams that are small and located in rural areas may cause less damage if they are overtopped or fail.
How Old Are Most U.S. Dams?
There are more than 91,000 dams across the U.S., in all 50 states, with diverse designs and purposes. The average dam age is 57 years, and more than 8,000 dams are over 90 years old.
