The High Cost of High-Hazard Dams

ASCE-report-cardIt is well known that our nation’s infrastructure is in desperate need of repair or replacement. In fact, the American Society of Civil Engineers (ACSE) 2017 Report Card has given our country’s infrastructure an overall grade of D+. Dams are a part of that critical infrastructure, and they have received an abysmal D grade from ASCE. We have over 90,000 dams in our country, and the average age of these dams is 56 years old. Considering that dams built 50 years ago were not designed for current standards and usually have inadequate spillway capacity, these numbers are concerning.

Even more alarming, America has nearly 15,500 high-hazard dams, with over 2,170 of these being deemed deficient. A dam is rated high-hazard when dam failure could result in the loss of human life, and deficient when it is at serious risk of failure. A deficient, high-hazard dam is a tragedy waiting to happen. Also, considering the estimated cost to repair these deficient, high-hazard dams is almost $45 billion, it is apparent that we have a dam crisis on our hands.

About Dams

Lake Mead, impounded by the Hoover Dam, is one of the most popular vacation spots in the country.

Dams provide significant economic and social benefits to society, including flood control, water storage, irrigation, debris control, and navigation. In addition, around 3% of our nation’s dams provide hydroelectric power — a clean, renewable energy source — accounting for 35% of our country’s renewable energy and 10% of our total power needs. And, of course, the most frequent function of dams is recreation. Dams impound eight of the top ten most popular vacation lakes in the United States, accounting for millions of tourist dollars and some of our country’s most beautiful and enjoyable areas.

The Mill River Dam collapse was the first manmade dam disaster and one of the worst of the 19th century. On May 16, 1874, the Mill River Dam in Williamsburg, MA failed, killing 139 people and wiping out four towns in western Massachusetts within one hour.

Catastrophic dam failures have occurred in the United States for well over a century, resulting in the deaths of thousands of people and causing millions of dollars in damages. This year, we narrowly avoided a disaster when California’s Oroville Dam stabilized after threatening to fail. During the crisis, over 188,000 people were displaced due to mandatory evacuations of the area. Although the Oroville Dam crisis thankfully ended without loss of life, the cost to repair the spillway is estimated to be $275 million. In 2003, the Silver Lake Dam in Michigan failed, causing approximately $100 million in property damages and putting over a thousand miners out of work. In 2004, the Big Bay Lake Dam in Mississippi failed, destroying 48 homes and seriously damaging 53 others. In 2006, the Ka Loko Dam in Hawaii failed, killing seven people and releasing nearly 400 million gallons of water, causing significant property and environmental damage.

Click on the image for an interactive map of dams in Massachusetts.

High-hazard dams are cause for concern in every state in the nation. In Massachusetts, 1,453 dams are included in the National Inventory of Dams, 333 of which are high-hazard. Of those, about 50 are classified as “poor” or “unsatisfactory” and in urgent need of repair. If any of these dams were to fail, there is a high likelihood that there would be a loss of human life. Dam failure is most frequently caused by overtopping, accounting for 34% of all dam failures. Causes of overtopping include inadequate spillway design, blocked spillways, settlement of the dam crest, and floods exceeding dam capacity. Other causes of dam failure include foundation defects such as slope instability and settlement (30%); piping, resulting in internal erosion caused by seepage (20%); and other causes including structural failure of materials, settlement and resulting cracking, poor maintenance, and acts of sabotage (16%).

Safety Programs

Draw down and cut off of releases from the damaged spillway at Oroville Dam. Taken on Feburary 27, 2017. Dale Kolke/California Delpartment of Water Resources.

The National Dam Safety Program (NDSP) was signed into law in 1996. NDSP was established to improve safety and security around dams by providing assistance grants to state dam safety agencies to assist them in improving their regulatory programs; funding research to enhance technical expertise as dams are built and rehabilitated; establishing training programs for dam safety inspectors; and creating a National Inventory of Dams. Every state in the nation excepting Alabama has a dam safety program, and 41 states also have Emergency Action Plan (EAP) requirements. A detailed and up-to-date EAP is critical to a successful dam safety program for high-hazard and significant-hazard dams. States without EAP requirements are Alabama, Georgia, Illinois, Iowa, Kentucky, North Carolina, Vermont, Wyoming, and — believe it or not — California.

Unfortunately, about one-third of our nation’s high-hazard dams lack an EAP. In addition, state dam safety programs are sorely underfunded and understaffed, and many of our nation’s deficient dams are not being repaired or rehabilitated in a timely manner. Why? State dam safety programs provide the inspection, permitting, recommendations, and enforcement authority for 80% of our nation’s dams, yet the average ratio of dams to dam safety inspectors is 207:1. Also, about two-thirds of our nation’s dams are privately-owned. Without enforcement of repair recommendations, some dam owners simply choose not to sink any money into their deficient dam.

The Ka Loko Dam breach in Hawaii resulted in the deaths of seven people, including a pregnant woman and a toddler.

For example, the Ka Loko Dam in Hawaii was privately-owned, and owner James Pflueger was sentenced to seven months in prison in exchange for a plea of no contest to reckless endangering. By entering the plea, prosecutors agreed to drop the seven counts of manslaughter. But admittedly, the dam failure was the result of a series of negligent events. The State of Hawaii, like most states in the nation, had a shortage of dam inspectors, and the Ka Loko Dam had not been adequately inspected. Also, Pflueger performed unpermitted construction activities at the dam, including grading and filling in the spillway. The County of Kauai ordered Pflueger to cease and desist all illegal grading operations, yet Pflueger ignored the order with help from then-Mayor Maryann Kusaka, who served as mayor of Kauai from 1997-2004. He also knew that there was seepage at the dam prior to the failure.

Key Issues 

The Wachusett Dam in Clinton, MA is a high-hazard dam, rated in satisfactory condition.

Clearly, the Ka Loko Dam failure was due to gross negligence and was completely avoidable. To avoid similar tragedies in the future, all of the key issues facing our nation’s dams should be addressed. First and foremost, our country needs to invest in infrastructure and to prioritize funding of dam safety programs. It is imperative that dam safety agencies have adequate personnel and resources to enforce inspection, repair, and rehabilitation recommendations. Also, since two-thirds of our nation’s dams are privately-owned, lack of funding for private dam upgrades is a huge problem. Adequate maintenance and rehabilitation of dams is costly, ranging from thousands to millions of dollars, and many private owners simply cannot afford these costs. Because of the high risk of high-hazard dams, our nation must prioritize funding assistance and loan programs to both public and private owners. It is also crucial that high-hazard dams have an up-to-date EAP, including action plans as well as notification and evacuation procedures, so that authorities are prepared and residents living downstream of the dam are protected. And speaking of residents, public outreach and awareness may be the most critical component of dam safety and awareness. The typical American citizen has no understanding of the role that dams play in our lives, or of the devastation that could come about from a dam failure. Even developers and officials are often in the dark about dams in their own communities. And, of course, everyone needs to understand that all high-hazard dams, no matter how seemingly structurally sound, are potentially dangerous and that there is inherent risk living in a dam break flood-prone area. Also, many of the private dam owners in our country are largely unaware of both their responsibility toward residents and businesses located downstream of their dam and of proper dam maintenance and repair procedures.

In Conclusion

We must change the way we manage our nation’s dams in order to prevent future catastrophes. The recent Oroville Dam crisis should serve as a warning to residents and legislators. As our dams age and climate change increases severe weather events, we must invest in the oversight, funding, and awareness of this critical infrastructure. Until we do, events such as the Oroville Dam crisis and the Ka Loko Dam failure may occur with increasing frequency, resulting in loss of life, environmental damage, and economic disaster.

National Dam Safety Awareness Day

There are over 87,000 dams in the United States. With one-third of those dams posing a serious threat to people’s lives and property if they fail, dam safety is nothing to ignore. Dams are a critical part of our infrastructure providing flood protection, water supply, hydropower, irrigation, and recreation. Although dam safety may not seem to be a big concern, dam failure can affect people for miles and miles, with sometimes fatal results. National Dam Safety Awareness Day is a day to acknowledge the progress we have made in making our dams safe structures and the continuous progress we still have yet to make.

Damage caused by Lake Delhi Dam failure in Iowa, July 27, 2010
Damage caused by Lake Delhi Dam failure in Iowa, July 27, 2010

As our population keeps growing, our dams are getting older and some are even deteriorating. A dam can fail within hours of the first signs of breeching. Dam safety is a shared responsibility. Dam owners, engineers, community planners, along with federal and state leaders all have important roles in keeping dams running efficiently and safely.

The National Dam Safety Program (NDSP), led by FEMA, has been working for 30 years to keep Americans safe from dam failures. The NDSP assists states in establishing and maintaining dam safety programs along with providing technical training to state and federal dam safety staff. Their support for research and development has greatly helped raise awareness about improper dam safety along with lessening the impact on a community if a dam were to fail.

Why Dams Fail

One of the most frequent ways dams fail is overtopping. Overtopping is a strong indicator of an unsafe dam. This can happen due to a number of reasons but typically it is from inadequate spillway design, debris blockage, or settlement of the dam crest. Overtopping accounts for about 34% of all dam failures in the United States and can also lead to erosion of the downstream face of the dam. Without proper maintenance of the downstream face, the dam is at a heightened risk of failure. Wind and other harsh weather conditions can cause waves to erode the upstream face which can make the dam unsafe during heavy rainfall or flash floods.

Missouri River Flood: Breeching of the levee at mile 550 in Aitchison County, June 19, 2011
Missouri River Flood: Breeching of the levee at mile 550 in Aitchison County, June 19, 2011

Other important factors that can cause dam failure are seepage and foundation defects. These defects account for about 30% of dam failures in the US, typically due to slide failure. If seepage or other factors weaken the soil supporting a dam, the overall strength of the dam greatly diminishes, creating the potential for a landslide-like affect.

Improper construction measures such as insufficient soil testing also contribute to dam failures. When permeable cavities or course gravel are present in dam foundations, seepage is a big concern because it erodes the soil at a fast rate. This often results in the dam settling or sinking which causes failure. A dam can fail by water passing under, over, through, or around it. Every dam should be properly connected to the ground and constructed using the best materials and methods to meet current design and construction standards.

How to Prevent Failures

When constructing and maintaining a dam, taking the proper engineering steps is vital. For example, completing sufficient soil tests prior to construction helps ensure that the dam will be adequately supported. The soil on the actual site should be examined before any detailed planning is put into place. It is also important to confirm the existence of impervious clay to seal the excavation and form the core of the bank. Failures can be prevented if the contractor is aware of any soil limitations at the site.

Teton Dam failure, June 5, 1976
Teton Dam failure, June 5, 1976

Dam failures have taken the lives of hundreds of people in recent decades so it is important to hire the right contractors to do the proper work. Nothing can take the place of a reliable and reputable contractor. Having experienced engineers and machine operators greatly reduces the risk of failure. It is important to review every employee’s credentials before starting a job and to always seek professional advice from an engineer when planning and designing a dam. Improper construction and inspection can lead to a weak structure, which can be dangerous and, sometimes, even fatal.

Maintenance and inspection must be routinely completed in order to keep dams safe. If a problem associated with a dam is not addressed in a timely manner, it can become more dangerous as time goes on. Dam inspectors should document every inspection in order to accurately assess needed repairs. While maintaining a dam, vegetation control, erosion repair, and clearing debris from spillways should be a routine practice.  A healthy layer of grass can help prevent erosion, and any debris within 25 feet of the dam should be removed. A poorly maintained dam can cost the owner more to repair than a dam which is regularly inspected and checked for needed repairs.

Emergency Action Plans

Damage left behind after the Teton Dam failure, Rexburg, Idaho, 1976
Damage left behind after the Teton Dam failure, Rexburg, Idaho, 1976

173 dams across the country have failed since 2005 so it is important to know what your community’s Emergency Action Plan (EAP) is if a local dam were to fail. An up-to-date EAP is critical to reduce the risk of lost lives and property damage. A good EAP accomplishes three main goals: identify the area below the dam that would be flooded, establish a line of communication for the dam owner and emergency response, and provide warnings and evacuations to be conducted by local emergency teams. Below are the six essential elements of a successful EAP.

  1. Notification Flowchart. This is to identify who should be notified by whom, and in what priority. This information is crucial for the notification of the persons in charge of taking emergency actions. The flowchart should have detailed information about each position in the chart such as title, office, and multiple ways of contacting that individual. EAPs should include the residents and businesses downstream of the dam that should be notified in case of an emergency. Proper communication and assigned roles can drastically reduce the impacts of a dam failure.
  2. Emergency Detection, Evaluation, and Classification. This ensures that the appropriate course of action is taken based on the urgency of the situation. Having procedures in place to classify an emergency situation properly will better prepare a community to activate their EAP before a catastrophe occurs. Early detection of a potential problem can save hundreds of lives and millions of dollars in property damage.
  3. Responsibilities. When an emergency occurs, everyone should know their role in reacting to the situation. Typically, the dam owner’s responsibilities include developing, maintaining, and implementing the EAP while state and emergency management officials are responsible for warning and evacuation. Without proper assignment of responsibilities, the EAP would be ineffective.
  4. Preparedness. This section outlines actions to be taken before an emergency occurs. Preparedness actions are taken to moderate or minimize the effects of a dam failure and to identify specific responses to be taken in emergencies.
  5. Inundation Maps. An inundation map identifies the areas affected if a dam were to fail. This map is important in identifying a strategy to notify and evacuate areas in danger. These maps graphically display flooded areas and show travel times for wave front and flood peaks at critical locations.
  6. Appendices. This section contains information directly applicable to the actions of the dam owner and the emergency management parties. The appendices provide information that supports the material used to develop the EAP such as maintenance requirements and dam break investigations.

In Conclusion

Dams serve an important role in our nation’s infrastructure. Millions of people in every state rely on dams to bring them benefits such as flood control, water supply, irrigation, recreational areas, and renewable energy. Safe operation and maintenance is important to sustaining these advantages and avoiding disasters which are very often preventable.  Dams fail for a number of reasons but the primary source of failure is poor inspection and maintenance, inadequate design, and improper operation. Know your risk when it comes to dam failure in your community. Getting familiar with your community’s EAP and level of risk from a dam failure can greatly help you in an emergency situation. National Dam Safety Awareness Day is an opportunity to raise awareness about our nations deteriorating dams and to take steps in making them safer structures for our community.

Happy National Dam Safety Awareness Day!

Dam Safety in the United States

What are dams?

Oroville Dam is an earthfill embankment dam on the Feather River east of the city of Oroville, California and is the tallest dam in the country.
Oroville Dam is an earthfill embankment dam on the Feather River east of the city of Oroville, California and is the tallest dam in the country.

In general terms, a dam is any structure that obstructs or converts the flow of water in rivers and streams, and they frequently serve more than one purpose. Dams store water to compensate for fluctuations in river flow, and they also provide irrigation, hydropower, drinking water, flood control, and support for recreational activities. There are four main types of dams, and dams are often a combination of these different types:

Embankment dams are typically constructed from natural earth materials such as rock and compacted soil, and are therefore far less expensive than concrete dams. Therefore, not surprisingly, more than 80% of all large dams in the United States are embankment dams. Typically used to retain water across wide rivers, embankment dams have a triangular profile and an impervious core and are termed “earthfill” or “rockfill” depending on whether they are primarily comprised of earth or rock.

Gravity dams are constructed of concrete or stone masonry and span narrow river valleys with firm bedrock. They are designed to hold back water by simply using the weight of the dam alone to resist the horizontal water load pushing against it. Each section of the gravity dam is stable on its own, independent of any other dam section.

The Hoover Dam is a massive arch-gravity dam that was constructed during the Great Depression, and the project’s success helped usher several decades of major water projects funded by the U.S. government.

While arch dams are also constructed of concrete, they differ from gravity dams in that they are designed to transfer water loads to adjacent rock formations. Arch dams are constructed only in narrow canyons with strong rock walls that are able to resist the arch pressure at the foundation and sides of the dam. Arch dams are thin and require less material than any other type of dam.

Buttress dams are hollow gravity dams with a solid upstream side that is supported by a series of buttresses on the downstream side. Constructed of reinforced concrete, buttress dam walls are straight or curved and are extremely heavy, pushing the dam into the ground.

Dams in the U.S.

In the United States, there are approximately 84,000 dams. The average age of these dams is 52 years old, and by 2020, over 70% of our nation’s dams will be over 50 years old, which is the widely-accepted longevity of most dams. In addition, the number of high-hazard dams, which are dams whose failure would likely cause the loss of life, is on the rise. Currently there are over 14,000 high-hazard dams nationwide, with another 13,000 being labeled significant-hazard, meaning their failure would cause significant economic loss. There are over 4,000 deficient dams, meaning they are at serious risk of failure, and 2,000 of these deficient dams are also high-hazard. The cost to repair these dangerous dams is estimated to be about $21 billion.

Many of our dams were originally constructed as low-hazard dams, which have more lenient design criteria due to their location in non-developed areas, typically agricultural. However, with the nation’s population growth and extensive development, these dams are now located in populated areas and considered high-hazard. This trend is expected to continue as population steadily increases.

The Johnstown Flood, known as the Great Flood of 1889, occurred on May 31, 1889 after the catastrophic failure of the South Fork Dam on the Little Conemaugh River 14 miles upstream of the town of Johnstown, PA. The dam broke after several days of extremely heavy rainfall, unleashing 20 million tons of water from the reservoir known as Lake Conemaugh. With a flow rate that temporarily equalled that of the Mississippi River, the flood killed 2,209 people. National Dam Safety Day is celebrated on May 31 every year in memory of this flood.
The Johnstown Flood occurred on May 31, 1889 after the catastrophic failure of the South Fork Dam on the Little Conemaugh River 14 miles upstream of the town of Johnstown, PA. The dam broke after several days of extremely heavy rainfall. With a flow rate that temporarily equalled that of the Mississippi River, the flood killed 2,209 people and decimated the town (Main Street shown in photo). National Dam Safety Day is celebrated on May 31 every year in memory of this flood.

The federal government owns only 3,225 — about 4% — of our nation’s dams. The remaining dams, over two-thirds of which are privately owned, fall under the jurisdiction of state dam inspection programs, with no federal oversight or regulation. State dam safety programs provide the permitting, inspection, and recommendations, along with enforcement authority, for 80% of our nation’s dams. Only one state, Alabama, completely lacks a dam safety regulatory program, but the rest are sorely underfunded and understaffed. For example, the average number of dams per dam safety inspector is 207. It is indeed daunting that dam safety programs are largely responsible for public safety, yet lack the resources to effectively provide that safety.

What causes dam failure?

  • Overtopping causes 34% of all dam failures. Inadequate spillway design, blocked spillways, settlement of the dam crest, and floods exceeding dam capacity are all causes of overtopping.
  • Foundation defects such as slope instability and settlement cause about 30% of all dam failures.
  • Piping, resulting in internal erosion caused by seepage, causes 20% of all U.S. dam failures.
  • The remaining 16% of dam failures are the result of other causes including structural failure of materials, inadequate maintenance, settlement and cracking, and deliberate acts of sabotage.

What can we do?

Of the 14,726 high-hazard dams in the country, only 8,854 have EAPs in place
Of the 14,726 high-hazard dams in the country, only 8,854 have EAPs in place

The 2010 Iowa Lake Delhi dam failure cost our economy about $170 million between damages and economic losses, and the 2006 Kaloko Reservoir Dam failure in Hawaii killed seven people. To make matters worse, the Kaloko dam was over 100 years old and had never once been inspected prior to its failure. Our dams have been given a “D” rating from the American Society of Civil Engineers (ASCE) 2013 Infrastructure Report Card, and the ASCE has recommended steps to take to improve that rating, one of which is the development of Emergency Action Plans (EAPs) for 100% of our nation’s high-hazard dams by 2017. Only 66% currently have EAPs.

Having effective EAPs at all high-hazard, and most significant-hazard, dams in the United States is the most important step in reducing the risk for loss of life and property damage from dam failures, and it is absolutely critical that deficient high-hazard dams have updated EAPs in place. To that end, Tata & Howard has been working with the Connecticut Department of Energy and Environmental Protection (CT DEEP) this spring to perform over 40 dam inspections and update over 30 EAPs.

T&H VP Sal Longo, P.E., assisted CT DEEP with the inspection of over 40 dams this spring.
T&H assisted CT DEEP with the inspection of over 40 dams this spring. Shown above is Vice President Sal Longo, P.E., during an inspection.

Besides maintaining EAPs for high-hazard dams, ASCE recommends the following steps to address our nation’s dam infrastructure:

  • Reauthorize and fully fund the National Dam Safety Program (NDSP), which is a partnership of the states, federal agencies, and other stakeholders that encourages individual and community responsibility for dam safety.
  • Establish a national dam rehabilitation and repair funding program to cost share repairs to publicly owned, nonfederal, high-hazard dams.
  • Implement a national public awareness campaign to educate individuals on the location and condition of dams in their area.
  • Encourage incentives to governors and state legislatures to provide sufficient resources and regulatory authorities to their dam safety programs.
  • Require federal agencies that own, operate, or regulate dams to meet the standards of Federal Guidelines for Dam Safety.

In addition to local and federal oversight and regulation, there are a number of steps that the public can take to minimize the risks associated with dam failure:

  • Know your risk. Find out if you live in a dam breach inundation zone by contacting your local emergency management agency or by contacting your state dam safety program (
  • Know your role. Know the dams in your area where you live and work, and be aware of potential maintenance issues and report them to authorities immediately. Dam owners have the responsibility to maintain their dams and to have an EAP, especially for high-hazard dams, and should work with the federal or state regulator to comply with safety standards.
  • Take action. Inform your friends and neighbors about the benefits and risks associated with dams and have an evacuation route in place for your family and/or business should a dam fail. If you live below a dam, it is imperative that you maintain flood insurance.

In conclusion

Dams are an integral part of our infrastructure, providing many important benefits. A large percentage of our nation’s dams are in need of repair and updating, and our high-hazard dams are of particular concern. It is critical that all of us, including the federal government, states, communities, engineers, and private dam owners, work together to promote dam safety and education. Our future depends on it.

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