U.S. dams are aging and not made to withstand new climate extremes, increasing the risk of disastrous failures

Flood waters approached the top of the Wrightsville Dam near
Montpelier, Vt. (Montpelier police photo via The Boston Globe)

Often overlooked and mostly old, dams provide drinking water, energy and transportation across the U.S., and as the recent flooding in Vermont showed, many need repair and updates that take weather extremes into account. "Heavy rainfall in the Northeast on June 9-11, 2023, generated widespread flooding," writes Hiba Baroud for The Conversation, a journalism platform for academics. "One major concern was the Wrightsville Dam, built in 1935 on the Winooski River north of Vermont's capital city, Montpelier. The reservoir behind the dam rose to within 1 foot of the dam's maximum storage capacity, prompting warnings that water could overtop the dam and worsen already-dangerous conditions downstream or damage the dam. . . . There are more than 91,000 dams across the U.S., in all 50 states, with diverse designs and purposes. . . . The average dam is 60 years, and more than 8,000 dams are over 90 years old."

Besides age, climate change adds another reason for dam fortification. "Compounding the risk in ways that are not yet fully understood are the intensifying rains brought about by a warming planet. Warmer temperatures mean more water in the air and a roiled atmosphere that brings both periods of drought and the potential for deluge," reports Sabrina Shankman of The Boston Globe. Baroud reports: "Designing new dams and upgrading existing infrastructure will need to be based on updated design procedures that consider future climate projections. . . . While older dams aren't necessarily unsafe, they were constructed following outdated design standards and construction procedures and for different environmental conditions. That influences the likelihood and consequences of their failure during disasters."

The U.S. receives an "infrastructure report card" from the American Society of Civil Engineers every four years. "The most recent report card estimates that 70% of U.S. dams will be more than 50 years old by 2030," Baroud reports. "Overall, the report gave U.S. dams a 'D' grade and estimated that more than 2,300 high-hazard potential dams – those that could cause loss of life or serious property damage if they fail, based on the level of development around them – lacked emergency action plans. . . . Decommissioning or replacing dams can be complicated and cost-prohibitive. Regularly maintaining and upgrading older dams can be a cost-effective way to strengthen them and make them resilient to natural hazards."

While overtopping is the number one cause of dam failure, overall structural integrity is influenced by "how long water flows over a dam and the volume of water. . . its purpose, size and location," Baroud explains. "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."