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What Are the Most Dangerous Dams In the U.S.?

Thousands of dams around the country could be putting property owners at risk for floods. Find out where the most dangerous dams are and why dam safety is so important.

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Dams hold back billions of gallons of water, and if a dam fails, it can have deadly consequences. 

A dam failure can put many homes in imminent danger. “We are not talking of just flooding someone’s house. We are talking about covering their house,” explained one Massachusetts resident about a potential dam failure of a 220-acre privately owned lake.

This level of concern exists across the country, and when two Michigan dams failed in the summer of 2020, authorities warned that the nearby town could be submerged under nine feet of floodwater. About 10,000 people were quickly evacuated. 

A dam failure can be a critical risk to life while also causing significant property damage. After all, just one inch of water flooding a home causes about $25,000 worth of damage, according to FEMA. Just consider how much damage can be caused by an uncontrolled flow of billions of gallons of water. 

How Safe Are Dams in the U.S.?

Monitoring dam safety is more complex than you may realize. There are different standards and protocols across the country because dam safety inspections are often managed at the state level.

First, let’s look at dams with the potential to cause damage based on their location. The National Inventory of Dams database tracks which dams could be life-threatening or cause economic or environmental damage. About 15,621 dams in the county are known to have high-hazard potential. That’s about 17 percent of all dams. 

Now let’s consider overall structural stability. In the latest Infrastructure Report Card from the American Society of Civil Engineers, dams were given a “D” for safety. 

It isn’t easy to aggregate dam safety risks because of the multiple stakeholders involved in ownership and inspection. However, a two-year investigation from the Associated Press merged data on structural safety and potential for damage. 

Their analysis identified 1,688 dams that are currently rated in poor/unsatisfactory condition and where a dam failure would cause human death. These dams are some of the riskiest sites because the structure may not be safe, and if it fails, people could die.

Which Dams Are Most Dangerous?

To find out the most dangerous dams in the U.S., use the interactive map from AP to explore the 1,688 dams that are structurally unsafe and that could cause loss of life if they fail. This is the most comprehensive resource that covers all types of dams.

The U.S. Army Corps of Engineers has its own classification for which dams are the most dangerous, but their risk assessment only looks at the dams under its jurisdiction. The Dam Safety Action Classification (DSAC) has five tiers of safety rankings, from DSAC 1 for “very high urgency” to  DSAC 5 which is normal. 

Because dam safety also falls under the oversight of the Department of Homeland Security, the public doesn’t have access to full data on DSAC ratings. 

However, we do know that the Whittier Narrows Dam in Los Angeles County is one of the most dangerous dams in the county. A 2020 report says it “is the only DSAC 1 dam in the nation not in the design or construction phase yet.”

A DSAC 1 dam classification is defined as a dam is almost certain to fail within a few years under normal operations. If the Whittier Narrows Dam fails, “up to 1 million people could be affected in 25 cities downstream of this dam,” said the USACE. For FY2021, about $385 million has been appropriated for structural modifications to the dam. 

What Are the Most Recent Dam Safety Updates?

Of the 738 dams monitored by the Army Corps of Engineers, a limited number is inspected each year. 

The 2020 Annual Report from the agency details that 67 dam safety inspections were completed during the fiscal year. As a result, about 13 percent of the inspected dams had an increase in DSAC rating, indicating that they pose more of a risk.

Of the dam safety assessments completed in 2020, there are nine that are now rated as DSAC 2. Even though a DSAC 2 classification is not the worst possible rating, it’s still an urgent risk because the chances of failure during normal operations or because of heavy rains is “too high to assure public safety.”

2020 Dam Safety Ratings at DSAC 2

  • Magnolia Levee, OH
  • Jennings Randolph Dam, PA/MD
  • Kinzua Dam, PA
  • Canyon Lake Dam, TX
  • O.C.Fisher Dam, TX
  • Thomaston Dam, CT
  • Oahe Dam, SD 
  • Garrison Dam, ND
  • Carbon Canyon Dam, CA

What Issues Are Contributing to Hazardous Dams?

The largest dams in the U.S., like the Hoover Dam, hold back nearly nine cubic miles of water, but the size of the dam isn’t the most pressing safety concern. 

Three main factors that are creating a perfect storm for dam safety concerns are:

  1. Aging Infrastructure. There was a dam-building boom in the 20th century, and about 70 percent of dams in the U.S. are now more than 50 years old, according to the American Society of Civil Engineers.
  2. Cost of Maintenance. Dams are such massive building projects that repairs can be expensive. And as dams get older, the financial toll increases. The Army Corps of Engineers has estimated there’s a backlog of $20 billion needed to address DSAC1 and DSAC 2 dam safety concerns. That’s about 75 times the amount that was spent in FY2018 on dam safety studies and construction projects.
  3. Increasing Risks. Even while aging dams are deteriorating, there are elevated risks from external factors, including extreme weather events, runoff from upstream development, and more potential damage from population growth in risk zones. 

How Does Effective Water Management Prevent Dam Failure?

There’s no doubt that dams are engineering feats. As building and water management professionals, we know how powerful the force of water can be. But a safe dam requires more than the brute force strength of holding back large amounts of water. Dam safety means using effective water management. This is why a dam spillway is one of the most important dam safety features to manage an overflow event. 

Attribution: Practical Engineering – YouTube

By having a way to siphon off water from the reservoir or lake, spillways can prevent water levels from rising so high that it flows over the top of the dam. Once this occurs, the dam itself could collapse, which is the most damaging result. 

Importance of Water Management at Home

It’s not just dams that need to be prepared for heavy rainfall. Adding water safety mechanisms to your home can protect your structure and prevent flood damage. Water safety improvements may even lower your insurance premiums. 

To protect your home from water damage, most homeowners start by adding a sump pump with a battery backup. These systems will automatically pump water out of your basement or crawl space, and the battery backup will keep the pump running even if your power is knocked out. 

Some homes also benefit from flood vents, which work to protect the home’s foundation. As water levels rise outside of the home, flood vents allow the water pressure to equalize so the foundation walls can stay intact. 

You can also protect your home with other basement waterproofing or crawl space encapsulation measures. These methods keep out moisture seepage and can help prevent the buildup of hydrostatic pressure in the soil around your foundation. 

A free inspection from the country’s leading basement waterproofing and foundation repair experts can help you learn what steps you can take to protect your home from water damage. 

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