New dam failure case studies and new 'lessons learned' have been uploaded to Thank you to the researchers and reviewers who contributed. The site now has more than 20 case studies and more than 10 lessons learned, as well as 5 ASDSO webinars that can be viewed free of charge as part of a Cooperating Technical Partnership between FEMA’s National Dam Safety Program and ASDSO.


August 2019

Lesson Learned: The hazard classification of a dam can change over time (hazard creep).

Researcher: Ryan Schoolmeesters, P.E.
Reviewer: Doug Johnson, P.E.

Hazard creep, also known as risk creep, is a term describing the gradual increase in anticipated consequences of a dam failure due to infrastructure development either along the drainage below a dam or within the reservoir area upstream of the dam. Even though the physical condition of a dam may not have changed, hazard creep can result in an immediate adverse impact on the overall risk profile of a dam because the potential consequences component has increased. Increased potential consequences of dam failure can have a range of adverse implications for dam owners. However, the worst consequence would be for an owner to underestimate or ignore the increased risk. Dam safety officials, dam owners, and consulting engineers need to be vigilant to monitor for any proposed infrastructure development below their dams and work collaboratively to identify and address the potential consequences of dam failures during original design and throughout the life of the dam.


Case Study: Equalizer Dam (Colorado)

Researcher: John Batka, P.E.
Reviewer: Ryan Schoolmeesters, P.E.

With the growth in northern Colorado that has occurred in the last decade, many Low hazard dams that were once located in relatively unpopulated areas now have development around them elevating the consequences of a dam failure. “Hazard Creep” is the result of development in the watershed that may require a dam to be re-classified into a higher hazard classification, even if there were no previous deficiencies with the dam itself. New residential and infrastructure development below dams creates a host of challenges for dam owner’s including increased dam safety monitoring requirements, increased design standards, and increased financial liabilities. Equalizer Lake is one case where a dam, originally built in a rural area for storage of irrigation water, is now surrounded by a shopping center, condominiums, and commercial businesses. This case study highlights one such case where Hazard Creep caused the hazard classification of a dam to be changed from Low to High hazard and the challenges with designing a spillway that will safely meet the spillway criteria for a High hazard dam.


Case Study: Quail Creek Dike (Utah, 1989)

Researcher: Everett W. Taylor, P.E.
Reviewer: Nathaniel Gee P.E.

On the morning of December 31, 1988 cloudy seepage was observed at the downstream toe of the Quail Creek Dike. This was not the first time. Seepage was first observed downstream of the dike during initial filling in 1985 and 1986. Since that time several efforts to cutoff high seepage flows had been made including several rounds of foundation grouting, installing relief wells and constructing an upstream cutoff in conjunction with reservoir blanketing. While the efforts reduced seepage flows they had not eliminated them. Now the seepage was increasing and turbid. Equipment was mobilized, and a gravel filter installed over the seepage area. Despite the ongoing efforts however seepage flows continued to increase, reaching 70 cfs around 10:30 PM. Recognizing the extent of the situation, equipment and personnel were moved to safe locations and a downstream evacuation was ordered. At 12:30 AM on January 1, 1989, Quail Creek Dike failed releasing an estimated 25,000 acre-feet of water into the virgin river and downstream flood plain; the result of a breach 300 feet wide and some 80-90 feet deep. Damage from the breach was estimated at $12 million with no loss of life reported thanks to the evacuation efforts of emergency responders. Partially in response to the failure the Utah Legislature would go on to enact a stronger set of dam safety regulations.


July 2019

Case Study - Machhu Dam II (Gujarat, India, 1979)

Researcher: Nathaniel Gee, P.E.
Reviewer: Lee Wooten, P.E.

On August 10, 1979, monsoon storms poured over Gujarat, India.  Monsoon rainstorms were not uncommon in this part of India, but as the storm increased it was clear this was larger than the usual storm.  Flow began to increase down the Machhu river, first hitting Machhu Dam I and then turning downstream to Machhu Dam II. As the storm intensified, operators at the Machhu Dam II began to open gates to keep the dam from rising above maximum levels. By 1:30 AM all the gates were opened fully except for three gates that were not properly functioning. Despite the nonoperational gates the dam was passing 196,000 cubic feet per second (cfs), very close to its full capacity of 200,000 cfs. It wasn’t enough, and the water continued to rise. It was early afternoon on August 11, 1979 when water overtopped the earthen embankments on both sides of the masonry spillway leading to the failure of Machhu Dam II.


Lesson Learned - Dams should be thoroughly assessed for risk using a periodic risk review process including a site inspection, review of original design/construction/performance, and analysis of potential failure modes and consequences of failure. The completed review supports a case for taking risk-informed actions at individual dams and for prioritizing actions for an inventory of dams.

Researcher: Mark Baker, P.E.
Reviewer: Irfan Alvi, P.E. and Gregory Richards, P.E., CFM. Input was also provided by representatives from the Bureau of Reclamation, U.S. Army Corps of Engineers, and Federal Energy Regulatory Commission.

Past dam failures and incidents have shown that dams can fail from a wide variety of potential failure modes at loadings less than the design loads. Critical flaws in design/construction or deterioration may exist that are not visible during a dam condition inspection. To address these risks, the dam safety industry is moving toward adoption of performing periodic comprehensive reviews to evaluate the safety of dams. For example, such evaluations of dams can be based upon an in-depth risk assessment with identification of potential failure modes, their likelihood of occurrence, and consequences of dam failure. Such periodic risk reviews are being performed by the Bureau of Reclamation, the US Army Corps of Engineers, the Bureau of Indian Affairs, the National Park Service, the Tennessee Valley Authority, and others.  Completed reviews support a case for taking risk-informed actions at individual dams and for prioritizing actions for an inventory of dams.


May 2019

Case Study - Maple Grove Dam (Colorado, 1979)

Researcher: Ryan Schoolmeesters
Reviewer: Greg Richards

In an effort to increase water storage capacity and provide flood protection to the surrounding communities of Lakewood, Colorado, two inflatable Fabridams were added to the crest of Maple Grove Reservoir and spillway in 1977. Shortly before midnight on March 17, 1979, personnel of The Consolidated Mutual Water Company noticed one of the inflatable Fabridams was collapsing and allowing reservoir water to be released down the spillway. The sudden and unintentional spillway release prompted a midnight evacuation of approximately 2,000 people and caused damage to structures, streets, and culverts as well as stream bank erosion. Investigation into the cause of the rupture and failure of the Fabridam revealed the Fabridam’s vulnerability to vandalism. Though uncommon, additional investigation discovered similar cases of vandalism to Fabridams throughout the country further presenting a need for steps to be taken to avoid future incidents of vandalism. Precautionary measures to avoid future vandalism were taken at Maple Grove Reservoir including increased personnel surveillance, installation of alarm systems with visual and audio alerts, security lighting, and fencing to limit public access. As an additional precaution, an earthen fuse plug was constructed in the spillway approach channel to assure any unintentional deflation of the Fabridam would only release a minimal amount of water downstream. As the Fabridams reached the end of their service life in 2004, a decision was made to replace them altogether with two independent hydraulically-actuated steel crest gates. The crest gates are less susceptible to vandalism, provide greater confidence in the integrity of the Maple Grove Dam and Reservoir, and were determined to provide greater public safety.


Lesson Learned -  Site security is a critical aspect of dam safety that shouldn’t be overlooked or disregarded.

Researcher: Ryan Schoolmeesters
Reviewer: Frank Calcagno

More than 90,000 dams are included in the 2018 National Inventory of Dams (NID) database. According to the 2016 U.S. Department of Homeland Security (DHS) Dams Sector fact sheet, “Dams Sector assets irrigate at least 10 percent of U.S. cropland, help protect more than 43 percent of the U.S. population from flooding, and generate about 60 percent of electricity in the Pacific Northwest.” It is undeniable that the Dams Sector, including dams, levees, hydropower plants, and navigation locks, provide a wide range of economic, environmental, and social benefits, and serve a vital role in the national interest.

Unfortunately the economic, environmental, and public safety consequences of failure also makes the Dams Sector assets an attractive target for physical, cyber, and other deliberate attacks. Deliberate attacks are not new to the Dams Sector risk profile. There are well documented historical examples of deliberate physical attacks on Dams Sector assets, including the German Möhne and Eder Dams during World War II in 1943, the North Korean Sui-Ho Dam and hydroelectric facility during the Korean War in 1952, and numerous smaller scale domestic attacks on several U.S. dams as recent as 2016. In 2012, the U.S. DHS compiled and documented a list of over two dozen physical attacks on dams worldwide during the first decade of the twenty first century alone, with no indication of a drop in frequency during that time period. Adding complexity, the advent and growth of digital infrastructure and automated data collection with internet-facing components has opened the door to relatively new threats to the Dams Sector risk profile, as demonstrated by a cyber attack on a small U.S. dam in 2013. The evidence indicates that the Dams Sector assets will continue to be the target of deliberate attacks. It is therefore imperative that Dams Sector partners develop and implement appropriate risk reduction strategies to protect critical infrastructure. 


March 2019

Case StudyVajont Dam (Italy, 1963)

Researcher: Lee Mauney
Reviewer: Giorgia DeWolfe

In 1963, one of the most disastrous rockslides ever to occur, slid into the reservoir behind Vajont Dam in Italy, causing a massive wave to overtop the dam, destroying entire villages and causing more than 2,000 fatalities. Because of the magnitude of the event, the Vajont Dam incident is one of the most researched rockslides in the world, analyzed in technical papers, books and film. This case study can remind us of the hazards that exist at dams, even if a structure is considered safe and does not fail. In the years before the incident, the risk of a major rockslide and its consequences were normalized and as the event was proceeding, a clear, concise warning message was never issued. Vajont highlights the need for thorough geotechnical investigations during dam design, specifically reservoir slope stability analyses. Vajont Dam remains in place today and provides a unique and important educational opportunity for visitors. Compared with historic dam failure and incident case studies, Vajont is unique is many aspects, including:

• Vajont Dam did not fail and remains one of the highest dams in the world,

• The scale of the 1963 rockslide and resultant flood are unprecedented,

• Resultant flooding from the rockslide reached the population at risk almost immediately,

• The fatality rate is among the highest recorded dam failure or dam incident,

• Voluminous research has been conducted on the Vajont rockslide and surrounding geology since the incident.


Updated Lesson Learned - Dam incidents and failures can fundamentally be attributed to human factors.

Researcher: Irfan A. Alvi
Reviewer: Mark Baker

The field of “human factors” considers how and why systems meet or don’t meet performance expectations, with an emphasis on understanding and prevention of incidents and failures. The systems considered in human factors work, such as dams, typically include both human and physical aspects, and are sometimes referred to as “sociotechnical” systems. To prevent future dam failures, it is essential that dam safety professionals understand both physical factors and human factors, and how they contribute to failures or safety.

Thumbnail Photo: In 2017, the service spillway of Oroville Dam in California, the tallest dam in the US, failed to due to uplift of the slab and subsequent foundation erosion. This was followed by erosion and headcutting at the emergency spillway, which was used for the first time in its history during the incident, and prompted evacuation of about 188,000 people. A wide range of human factors contributed to the incident at individual, organizational, regulatory, and industry levels, starting with the design and construction of the project in the 1960s until the incident in 2017. (Photo Source: Irfan A. Alvi)


More 'lessons learned' and case studies coming in 2019!