New Studies Published on ASDSO's Dam Failure Website

As dam failures and incidents occur both nationally and internationally, there is a pressing need to understand the underlying causes of failure to help minimize such occurrences in the future. Current information on historical dam incidents is sometimes scattered, incomplete, missing, or misleading – making it difficult for owners and practitioners to easily access meaningful information that could assist them with critical design and operational decisions. If lessons learned and best practices are not effectively communicated, there is a possibility that poor practices will be repeated, and preventable incidents will not be averted.

Presented within are links to individual case studies and 'lessons learned' pages that summarize historical dam incidents and failures and the valuable information gleaned from them. Each page contains background and description, photographs, videos, best practices, and other resources related to the case study or lessons learned being addressed. The content of this website encompasses a range of failure modes, dam types, and dam safety topics, including best practices regarding engineering and design practices, human factors, emergency planning and response, operation and maintenance, and regulatory issues.

The site now has more than 50 case studies and more than 30 lessons learned in total. 

Thank you to all the contributors, the ASDSO Dam Failures and Incidents Committee, and the FEMA National Dam Safety Program, which provides research funding. 

September 2023

Case Study: Langley Dam (South Carolina, 1886)

Researcher: Jeffrey W. Munsey
Reviewers: Eric Halpin P.E.

The failure of Langley Dam, located near Aiken, South Carolina, is one of the more noteworthy and surprising far field (epicentral distance ~ 176 km) effects of the M7.0, August 31, 1886, Charleston, SC earthquake. Langley Dam, a relatively small earthen mill dam, was constructed on Horse Creek circa the Civil War. Almost immediately after the earthquake shaking ceased, Langley Dam failed and the discharged water damaged two railways, which caused two separate train derailments.  Two of the fatalities attributed to the Charleston earthquake were from crewmembers on the two trains.  Historical accounts of the dam failure integrated with recently completed geotechnical investigations and site response modeling are used to explain the surprising failure of Langley Dam.  Henry W. Grady, who was managing editor of the Atlanta Constitution newspaper, wrote an important historical account of the Langley Dam failure.  Mr. Grady left Atlanta for Charleston within hours of the main shock.  His detailed trip accounts provide a unique perspective on the aftermath of the Charleston earthquake.  In particular, his description of the post-failure condition of Langley Dam is critical in understanding how the dam failed.  The foundation conditions and geologic setting of Langley Dam, and the materials and methods used to construct the dam played key roles in its failure.  Recognition of the geologic conditions that contributed to the failure of Langley Dam has implications for seismic design of modern structures in similar settings in Georgia and South Carolina.

June 2023

Case Study: Sheffield Dam (California, 1925)

Researcher: Cory Miyamoto, P.E.
Reviewers: Nathaniel Gee, P.E. and Alex Pires-Sturm P.E.

Sheffield Dam is one of the earliest recorded case histories of earthquake-induced failure of an embankment dam. Constructed in 1917 near Santa Barbara, California, the 25-foot-high, 720-foot-long earth dam failed on the morning of June 29, 1925, after being subjected to shaking from a ML 6.3 earthquake event roughly 7 miles northwest of the dam site. The collapse of the dam caused flooding 1- to 2-feet deep in the lower parts of the city, though no fatalities were attributed to the dam failure. Later investigations into the cause(s) of the collapse identified liquefaction at the base of the dam as a key contributing factor in the failure.

Lesson Learned: Downstream flooding can be caused by spillway flows that exceed channel capacity or as a result of reservoir misoperation.

Researcher: Lee Mauney, P.E.
Reviewers: Bill Fiedler, P.E. and Greg Paxson, P.E.

If a dam functions as intended, risks to the dam owner and nearby communities are often assumed to be negligible. Experience suggests this may not always be the case – the immediate reservoir area and downstream floodplains could be subject to flooding from ‘normal’ yet large spillway flows that exceed channel capacity or as a result of spillway misoperation. In many locations around the world, human development downstream of a dam is often a direct result of the flood risk reduction provided by the dam. Here, lessons learned from example case studies are developed to highlight the implications of non-breach release events on downstream communities; Strategies for managing these risks are evaluated. Typically, dam safety risk assessments are focused on the potential for dam failure and uncontrolled release of the reservoir. However, non-breach impacts are more likely to occur. This increases the importance of estimating and communicating the potential for these events to downstream communities. It also supports dam owner planning and decision-making during normal and flood operations. In addition to reducing risks through communication, preparedness, and community resiliency, recognition and mitigation of non-breach risks to downstream populations may reduce potential liability for dam owners.

Lesson Learned: Drum gates are complex mechanical systems that must be carefully operated and maintained.

Researcher: Cory Miyamoto, P.E.
Reviewers: Russell Bowlus, Joshua Paquet, and Roy Arnold

Drum gates are a type of spillway control gate used to regulate reservoir level and provide flood control. Although more common for dams constructed prior to the 1950’s, many large dams in the United States and internationally are still equipped with drum gates. There are several documented case histories of past drum gates failures, as well as a history of operations and maintenance challenges for this gate type. Regular inspection and maintenance of drum gates and their associated components is necessary to ensure reliable operation. This includes both routine maintenance activities, such as regular gate testing, as well as careful planning and execution of more detailed inspections and/or repair work. Control systems need to be checked and updated, as needed, and operators must receive proper training on safe gate operation. Early warning systems, an up-to-date Emergency Action Plan, and close communication with downstream communities and first responders are also key components of improving safety and reducing risk in the event of a sudden release.

March 2023

Case Study: Banqiao Dam (China, 1975)

Researcher: Andy Lynch, P.E.
Reviewer: Seth Thompson, P.E.

In the summer of 1975, Typhoon Nina made landfall in China near Shanghai and progressed inland until colliding with a cold front over the Henan Province, which stopped the storm’s movement. Over three days, the storm dropped over 64 inches of rainfall, including 7.5 inches in one hour, and set the world record 6-hour precipitation of 32.7 inches. This deluge caused flooding throughout the region and quickly filled to capacity any available flood storage within the region’s flood control dams.
Banqiao Dam was one of those dams. It was constructed to provide flood control and irrigation water to the region. Built in 1952, Banqiao stood 80 feet tall and was constructed of a clay core surrounded by a sand shell. The dam was designed for a 1 in 1,000 event or 20.9 inches (530mm) over three days. Typhoon Nina greatly exceeded this and was estimated to have been a 1 in 2,000 event. Due to downed communication lines and inadequate discharge capacity through its five sluice gates and undersized secondary spillway, Banqiao Dam overtopped by approximately one foot on August 8, 1975. The devastating flood wave killed tens of thousands instantly and stranded millions without access to food or clean water. In the ensuing summer heat and as a result of starvation and disease, over 100,000 more died. In addition to the terrible natural disaster brought by Typhoon Nina, the Banqiao Dam failure has been described as one of the worst man-made disasters in history.

Case Study: Fujinuma Dam (Japan, 2011)

Researcher: Paul Risher, P.E.
Reviewer: Lee Wooten, P.E.

On March 11, 2011, a massive 500-600 km rupture off the east coast of Japan resulted in a powerful Magnitude 9.1 earthquake and subsequent tsunami. The shaking also damaged at least 745 dams in Fukushima Prefecture and caused a rare seismically induced failure of the Fujinuma Dam. The earthfill dam and an earthfill saddle dam were built in layers from 1937 to 1949 to store irrigation water. 
Observations and analyses concluded the dam had poor compaction and foundation treatment, likely resulting in a seismically induced slope failure that lowered the crest below the reservoir level. The saddle dam and multiple slopes around the reservoir rim also had slope failures, likely due to rapid drawdown.

February 2023

Case Study: Hebgen Dam (Montana, 1959)

Researcher: Lee Mauney, P.E.
Reviewers: Ivan Wong, P.G., Khaled Chowdhury, P.E., Ph.D., Stephen Benson, P.E., Steve Samuelson, P.E., and Dave Gillette, P.E.

Just before midnight on August 17, 1959, in southwest Montana, an Mw 7.3 earthquake caused a block of the earth's crust 125 square miles in area, including Hebgen Lake, to subside along established faults north of the reservoir. Up to 21 feet of vertical displacement was measured along the segment of the Hebgen Fault near the dam. The earthquake caused a massive rockslide to cross the Madison River and up the opposite canyon wall. Rockslide debris dammed the river, forming Quake Lake just downstream of Hebgen Dam. As water began rising behind the slide, officials feared that the mass would be overtopped and breached or that water in Quake Lake would rise to the toe of Hebgen Dam, potentially destabilizing that dam. Working around the clock, a discharge channel was excavated through the slide mass, lowering the lake to a safe level. Ground deformations from the earthquake also damaged Hebgen Dam, cracking the concrete core wall, damaging the spillway, and inducing a seiche on Hebgen Dam reservoir, causing waves to overtop the earthfill dam. The failure of the dam and uncontrolled release of Hebgen Lake would have been catastrophic for the downstream population at risk. Although severely damaged, Hebgen Dam did not fail and was later repaired.

Case Study: Guajataca Dam (Puerto Rico, 2017)

Researchers: Sam S. Hutsell, P.E.; Carlos E. Cepero, P.E.; and Todd N. Loar, P.G., CEG
Reviewers: Dennis Zeveney, P.E. Jose Bermudez, Gregg Batchelder Adams, P.E. John Kendall, P.E. Thomas Terry, P.E. and Sam Hutsell, P.E.

Guajataca dam is located in northwest Puerto Rico and is a hydraulic fill core embankment dam designed and constructed in the 1920s to provide irrigation and municipal water to the region.  In September 2017, about two weeks after Hurricane Irma passed to the north, the island was directly impacted by Hurricane Maria.  The precipitation resulted in discharge flows through the spillway that exploited design flaws and structural defects causing undermining and removal of spillway slabs; head-cutting; partial erosion of the stabilization buttress; and failure of portions of the downstream concrete chute leaving a large scour hole in the lower half of the spillway.

The initiation of erosion was attributed primarily to the poor alignment of the spillway with respect to the river that resulted in flows spilling off the lower left side in an area with no scour protection.  The flows caused erosion and head cutting of the weak underlying foundation materials that subsequently undermined the spillway chute and caused the lower concrete slabs to fail.  Most of the project was constructed on a large, active, translational landslide complex that has caused significant, ongoing distress to the dam and spillway structure since initial construction.  The damaged condition of the spillway and eroded embankment and stability berm raised concerns that continued spillway flows would further erode the foundation and enlarge the scour hole resulting and head-cutting creating a direct connection with the pool and/or cause removal of the stabilization buttress that could accelerate the foundation landslide and jeopardize the integrity and safety of the dam.

The US Army Corps of Engineers (USACE) was engaged to support the dam owner and provide emergency measures to stabilize the failed spillway; restore the downstream stabilization buttress; protect the dam from further erosion; and develop Interim Risk Reduction Measures (IRRM*) to mitigate the failed structure and compromised buttress.

*Note: although IRRM’s may represent significant structural repairs, they are not considered by USACE to be a long-term permanent fix that mitigates all spillway or dam potential failure modes that may be actionable at this dam.

Lesson Learned: Forensic investigations are needed for major dam failures and incidents in order to determine the history of the contributing physical and human factors, and the culminating physical failure modes and mechanisms.

Researcher: Mark E. Baker, P.E.
Reviewers: Nathaniel Gee, P.E. and Irfan Alvi, P.E.

Forensic investigations are needed for major dam failures and incidents in order to determine the history of the contributing physical and human factors, and the culminating physical failure modes and mechanisms.  Forensic investigations also often yield valuable information on lessons to be learned by the dam industry in order to prevent similar failures in the future. Forensic investigations can also aid in the rebuilding or repair of a dam following the event. 

Lesson Learned: Natural dams can form quickly through processes such as landslides, avalanches, and river ice jams. In some cases, the formation of natural dams requires prompt intervention to protect people and property.

Researcher: Mark E. Baker, P.E.
Reviewer: Dan Jantzen

While the focus of dam safety is appropriately on manmade dams, practitioners need to be aware that nature also forms dams that can fail with devastating results. These dams can form quickly and form large dams through such processes as landslides, avalanches, glacial ice movement, and river ice jams. In some cases, a prompt intervention response is needed because the watercourse impounded by a natural dam can quickly become a lake and become a hazard. Dams formed from landslides, glacial ice, and neoglacial moraines are the natural dams that present the greatest threat to people and property¹.  This lesson learned is to make the reader generally aware of the natural dams that have the most potential to become a risk. Specific geologic formation and failure mechanisms of natural dams can be found in the references.

November 2022

Lesson Learned: Dams in cold regions should account for ice.

Researcher: Mark E. Baker, P.E.
Reviewer: Boyd Howard, P.E.

Most of the 90,000 dams in the U.S. experience cold and freezing conditions for at least part of the year. Dam failures during the winter can release large blocks of ice from the reservoir that can increase destruction and loss of life in the dam failure flood downstream. For dams on rivers, dam engineers should investigate the potential for ice runs and mitigate the risk of ice runs should they exist. In addition to ice runs, cold weather ice can affect the operation of dam gates and other equipment. Equipment should be designed, operated, and maintained for ice and winter conditions. Importantly, all dams in cold weather regions (not just river dams) pose hazards to dam operators in carrying out their dam inspection, operation, and maintenance activities. For all dams in cold regions, dam engineers should make conditions safe for operators who may need to inspect, operate and maintain dams in severe cold and icy conditions.

Case Study: New Orleans Levee System (Louisiana, 2005)

Researchers: Eric Halpin, P.E. and Rich Varuso, Ph.D. P.E.
Reviewer: Rich Varuso, P.E.

During August of 2005, Hurricane Katrina made landfall just south of New Orleans, Louisiana, resulting in the largest release of energy ever recorded in North America. The CAT 5 hurricane caused storm surge and wave impacts of 15 to 28 feet across the Mississippi River delta region that was estimated to be between a 50-year and 500-year recurrence interval, depending on the location within the region.  The hurricane caused a reversal of flow (upstream) of the Mississippi River.  Multiple locations within the levee system were breached during Hurricane Katrina, resulting in over 1,800 lives lost, billions in economic damage, and a long-term redistribution of over half the city’s population.

September 2022

Case Study: Hawkins Dam (Washington, 2014)

Researcher: Douglas L. Johnson, P.E.
Reviewer: Mark E. Baker, P.E.

On Thursday, August 21, 2014, the fire-swept Benson Creek watershed received from 0.4 to 0.9 inches of rain in one hour - about a 5-year event. There were high runoff flows and numerous mudslides throughout the watershed. As a result of this flooding, Hawkins Dam failed through headward erosion in its emergency spillway.  Subsequent analyses showed that due to the fire, the soils of the watershed had greatly reduced infiltration parameters (hydrophobic soils), resulting in post-fire runoff flows on the order of 7 to 8 times the estimated pre-fire flows for the same rainfall event.  It was estimated that the post-fire runoff flows from the August 21 5-year storm exceed the estimated pre-fire runoff flows from a 1,000-year storm event.

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