Heavy rainfall poses risks for dams to overtop and overflow, causing uncontrolled release of impounded water downstream.
When dams fail or breach, the result could be catastrophic. Surging water downstream can destroy lives and properties on its path.
The Conversation article reports that extreme rainfall made more frequent and intense by climate change is increasing stress on thousands of US aging infrastructure.
A combination of factors makes dams highly susceptible to dam breach and failure – a hazardous event in the form of heavy rains and the dam’s structure, which can be old, poorly maintained, and poorly designed – those that do not have adequate spillway capacity to release water safely.
Generally, concrete dams are less risky for overtopping than those made with earthen embankments.
The article notes that 34% of all dam failures in the US are caused by overtopping. The consequences of overtopping dams depend on certain factors like their size, purpose, and location and whether they are designed for flood protection and are close to homes, businesses, and critical infrastructure. Dams in rural and less populated can result in less damage if they overtop or breach.
Condition of dams in the US
There are more than 91,000 dams across the US, with an average age of 60. According to the American Society of Civil Engineers, about 8,000 dams, or close to 9%, are over 90 years old, and 70% will be over 50 by 2030.
The ASCE gave a grade of “D” to all its dams and estimates that at least 2,300 are “high hazard potential dams”, a classification standard issued by the US Federal Emergency Management Agency (FEMA), which means that its failure will cause loss of human life and significant property destruction.
Fixing vulnerable dams
The most cost-effective way to ensure these dams don’t feel and cause havoc is to regularly maintain and upgrade older dams to strengthen them and make them resilient to natural hazards.
Decommissioning or replacing them will be very complex and expensive. When dams no longer serve their purpose, they can be removed to restore the river’s natural flow.
The cost of rehabilitating all non-federal dams is US $157.7 billion. Of this amount, $34.1 billion is the estimated cost of rehabilitating high-hazard potential dams. However, the article says that only around $3 billion is provided by the 2021 Infrastructure Investment and Jobs Act for dam safety projects, focusing on rehabilitation, retrofitting, and removal.
The impacts of climate change do not spare the US, as it has recently experienced many extreme events. Torrential downpours hit the northeastern parts at the end of September 2023, causing widespread floods and destruction, particularly in New York City, where many of its subway stations and streets were affected.
The article notes how the heavy rains of June 9-11, 2023, have threatened Vermont’s Wrightsville Dam to overtop when water levels reach within a foot of the dam’s maximum storage capacity. Overtopping of the Wrightsville Dam, built in 1935, could worsen the already dangerous conditions downstream or damage the dam.
Increased extreme events in the US should spur the government and communities to prepare and plan for disasters. Dam failure could have a far-reaching impact, affecting water supplies, energy generation, and transportation, as many are also part of the large navigation networks in the US and the economy as a whole. It is essential to understand the direct and indirect costs when critical infrastructure like dams fail.
Designing dams to adapt to climate change
The article also mentions that “designing new dams and upgrading existing infrastructure will need to be based on updated design procedures that take into account future climate projections, not just historical hazardous events” (Baroud, 2023).
Baroud (2023) says further, “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.”
Baroud, H. (2023, July 14). Climate change is increasing stress on thousands of aging dams across the US. The Conversation. Retrieved from https://theconversation.com/climate-change-is-increasing-stress-on-thousands-of-aging-dams-across-the-us-209568
Rehabilitation Of High Hazard Potential Dam (HHPD) Grant Program. (2023, September 26). FEMA. Retrieved from https://www.fema.gov/emergency-managers/risk-management/dam-safety/rehabilitation-high-hazard-potential-dams
Borrenstein, S. (2023, April 2). Why the US is leading the world in extreme weather catastrophes. PBS. Retrieved from https://www.pbs.org/newshour/science/why-the-u-s-is-leading-the-world-in-extreme-weather-catastrophes
Weather tracker: heavy rain brings flash flooding to New York City. (2023 October 2). The Guardian. Retrieved from https://www.theguardian.com/environment/2023/oct/02/weather-tracker-heavy-rain-brings-flash-flooding-to-new-york-city