As dam failures and incidents occur both nationally and internationally, there is a pressing need to understand the underlying causes for failure to help minimize such occurrences in the future. Current information on historical dam incidents is scattered, incomplete, missing, and sometimes 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 as well as 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 contents of this webpage encompass 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. 

Seven case studies and three lessons learned have been added in 2021, with more currently being researched. The site now has more than 30 case studies and more than 20 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.


October 2021

Case Study: Toddbrook Reservoir Dam (England, 2019)
Researcher: Lee Mauney
Reviewers: Bill Fiedler and Thomas Hepler
Toddbrook Dam (sometimes referred to as Whaley Bridge Dam) was constructed in 1840 with a single spillway at the left abutment of the dam. In 1964, the spillway was damaged during a flood event. This damage led to modifications to increase spillway capacity, and a concrete auxiliary spillway chute was constructed on the downstream fill. During a flood event in 2019, a single slab of the auxiliary spillway chute collapsed into a large void that had formed underneath. The void then enlarged (removing some of the downstream shell material), and more slabs collapsed, risking the integrity of the dam. More than 1,500 people were evacuated in the town of Whaley Bridge for six days. An immediate drawdown of the reservoir was initiated, and urgent measures were taken to stabilize the dam.

Case Study: Glen Canyon Dam (Arizona, 1983)
Researcher: Andy Lynch
Reviewers: Paul Schweiger and Seth Thompson
In the summer of 1983, Glen Canyon Dam and its reservoir, Lake Powell, experienced higher-than-normal inflows. Despite National Weather Service forecasts predicting high spring runoff, Lake Powell was maintained at near 100% capacity, leaving very little storage capacity to attenuate the high inflow rates. On June 2, Glen Canyon Dam began releasing flows through the left spillway. On June 6, the dam’s operators heard vibrations coming from the spillway tunnel and observed material being discharged from the outlet. The configuration of the dam’s two spillways had left them vulnerable to damage from cavitation due to the very high velocities within the spillway tunnels. There was a very real concern that erosion of the spillway tunnels could undermine the dam’s foundation and cause the entire dam to fail. Over the following weeks, the dam’s operators regulated discharges through the damaged spillways in order to prevent uncontrolled discharge or even overtopping of the dam. Throughout the whole ordeal, the operators knew that damage to the spillways was continuing, but unsure of the rate or extent of the damage. Ultimately, the operators were successful in passing the high flows and the spillways at Glen Canyon Dam were repaired and retrofitted to prevent cavitation from reoccurring in the future.


September 2021

Case Study: El Guapo Dam (Venezuela, 1999)
Researcher: Seth Thompson
Reviewers: Paul Schweiger, Bill Fiedler, and Lee Mauney
The El Guapo Dam (constructed 1980) provided flood control and served as the principal source of potable water and irrigation for the Barlovento Region in the state of Miranda, Venezuela. Between December 1999 and January 2000, Venezuela experienced the most extreme period of rainfall ever recorded in the country, 23.14 inches were recorded at Maiquetía, Vargas, Venezuela (exceeding the 0.1% AEP event for many drainages); these events were concentrated over three states: Falcon, Miranda, and Vargas. On December 16th, the resulting runoff caused El Guapo’s reservoir level to rise to within 8 inches of the dam crest (19 feet above normal pool). The spillway chute walls began to overtop and embankment material along the landside of the spillway walls began to erode. Shortly after the chute walls overtopped, the governor of Miranda ordered the evacuation of the downstream population of approximately 10,000 people. The erosion of the embankment and eventual undermining of the spillway structure led to the breach of the reservoir through the spillway area, releasing the upper 98 feet of the reservoir at an approximate peak discharge of 1.8 million cfs. The flood wave, estimated between 25 and 40 feet, killed 10 people, and injured or otherwise affected 11,000 to 15,000 others; destroyed 790 homes and damaged 1,500 others. The dam has since been reconstructed with an RCC foundation for the upgraded spillway (three and a half times as wide as the original), that was designed for the probable maximum flood (PMF), and a new normal pool level 13.1 feet below the original level.

Case Study: Walnut Grove Dam (Arizona, 1890)
Researcher: Nathaniel Gee
Reviewer: Paul Risher
Walnut Grove Dam was constructed at a site approximately 20 miles northeast of Wickenburg, Arizona. Gold had been discovered in the area and a New York Investor Wells H. Bates wanted a dam built in order to supply water for hydraulic mining. He acquired the mining rights and then hired William P. Blake a renowned geologist to design and construct the dam. However, he was fired shortly after beginning work. He was replaced by EN Robinson a civil engineer from San Francisco. Robinson was unable to salvage any of the construction that Blake had begun and no design documents were available, so he largely started over. It is unclear exactly why, but he was then replaced by one of the New York Investors brothers who had no engineering or construction experience. Managing a dam construction project from over 2,000 miles away presented many challenges. During the construction, there were frequent complaints about low pay, poor oversite and quality control, an untrained workforce, and high construction and design costs. Work was being done on the spillway when on February 16th 1890 it began to rain. It would rain on and off until February 22nd. This rain-on-snow flood event caused the dam to overtop, leading to failure on February 22, 1890.

Case Study: Testalinden Dam (British Columbia, 2010)
Researcher: William Johnstone
Reviewer: Mike Noseworthy
At approximately 2:15 pm on Sunday, June 13, 2010, a privately-owned earthen dam on a man-made reservoir on Testalinden Creek failed, causing a debris and mud torrent that travelled 7 km downstream to severely impact a number of homes and an agricultural area located 7 km south of Oliver, British Columbia. Fortunately, there was no loss of life. Although the dam was not large and had a very small impoundment, the estimated breach outflow volume of between 20,000 to 29,000 m3 combined with saturated silty soils in the steep downstream channel to produce a very large debris flow that was an estimated 250,000 m3 in size by the time it reached the alluvial fan in the main valley below.
In addition to detailed investigations of the factors that contributed to the Testalinden Dam failure, this failure led to important changes to dam safety regulation and oversight in British Columbia. Over 1,100 dams in the Province were evaluated under a Rapid Dam Assessment (RDA) program, the Provincial Dam Safety Regulation was amended, a new Professional Practice Guideline for Dam Safety Reviews was developed, education and awareness programs were offered to dam owners, and Provincial dam safety reports are now published annually.

Lesson Learned: Concrete-lined spillways are vulnerable to significant damage and potential reservoir breach if flows are not safely contained within the conveyance structure.
Researcher: William Fiedler
Reviewers: Tom Hepler and Lee Mauney
Concrete conveyance structures, such as chutes or tunnels are typically used to safely convey spillway discharges from the reservoir to the river channel downstream. If the conveyance structure concrete lining is compromised, the foundation can be subjected to high velocity flow, which has the potential to erode the foundation, progressively removing more of the concrete lining and headcutting back to the reservoir, leading to reservoir breach. There are several mechanisms that can fail the concrete lining of a spillway conveyance structure, including flotation, stagnation pressure, cavitation, ball milling and overtopping of chute walls. The design and evaluation of existing spillway conveyance structures should consider the potential for these failure mechanisms and appropriate defensive design measures should be implemented.

Lesson Learned: Gates and other mechanical systems at dams need to be inspected and maintained.
Researcher: Cory Miyamoto
Reviewer: Josh Paquet
Many dams rely on gates to control and regulate reservoir levels and releases, allowing for operational flexibility and safeguarding the public downstream during large floods. As such, it is essential that gates and other related mechanical systems are regularly inspected and maintained in order to ensure the continued safe and reliable operation of the associated dam infrastructure. Gates and mechanical systems that are well maintained and regularly exercised can typically be relied upon to perform as designed when operated.


June 2021

Case Study: Spencer Dam (Nebraska, 2019)
Researcher: Mark E. Baker
Reviewers: Martin Teal, Rob Ettema, and John Trojanowski
Spencer Dam failed during a major early morning ice run on the Niobrara River during a bomb cyclone weather event on March 14, 2019. Large, truck-sized ice rubble caused ice jams along the river. These ice jams failed causing new surges of ice and water. There was no warning to the dam operators. When the ice run reached Spencer Dam, the gates likely jammed with ice restricting flow. The reservoir quickly filled, and the embankment section of the dam overtopped and failed in two locations. One resident in a house 1/3 mile downstream did not evacuate and was later declared dead by drowning.  This dam failure case study offers many valuable insights, including (1) river ice run formation, transport, and infrastructure vulnerability (2) the need for Emergency Action Plans and evacuation exercises (3) the need for accurate Downstream Hazard Classification, and (4) the need to research a dam’s history and keep accurate records. The reader is encouraged to read Chapter 7 Lessons Learned of the Spencer Dam Failure Investigation Report. 


February 2021

Case Study: Columbia River Levees (Oregon, 1948)
Researcher: Meghan Walter
Reviewer: Steve Durgin
On May 30, 1948, rising floodwaters of the Columbia River breached a railroad fill acting as a levee and flooded the city of Vanport, Oregon. At the time, Vanport was Oregon’s second largest city and World War II’s largest federal housing project. Located in the marsh between the Columbia River and the Columbia slough, a system of levees protected Vanport from the floods of the Columbia River. At 4:17 pm on May 30th, Memorial Day 1948, a railroad embankment on the western end of the levee system collapsed under the pressure from the river, sending waves of water into Vanport. In less than a day, the nation’s largest housing project – and Oregon’s second largest city – was destroyed and 18,000 residents were displaced from their homes. Following the flood, the city was not rebuilt. The area is now home to a golf course, the Portland International Raceway, and recreational wetland areas. 

Lesson Learned: Floods can occur due to unusual or changing hydrologic conditions.
Researcher: Everett Taylor
Reviewer: Gregory Richards
Floods can trigger a significant response from dam owners and operators. The events caused by flooding may range from needing to pass large flows to overtopping and possible failure of the dam. Consequently, dam owners are tasked with monitoring weather patterns and runoff to effectively operate their facilities during hydrologic events. Unusual or changing conditions in the watershed, however, may result in larger than expected runoff events that can surprise owners and operators. These conditions may include rain on snow events, frozen or saturated ground, burned watersheds, and more. In addition to tracking weather and runoff predictions, dam owners and operators should be aware of the conditions in their contributing watersheds and consider the effects those conditions may have on runoff to their dams and reservoirs.