A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than 200 notable dam failures happened worldwide.
A dam is a barrier across flowing water that obstructs, that directs or slows down the flow, often creating a reservoir, lake or impoundments. Most dams have a section called a spillway or weir over or through which water flows, either intermittently or continuously, and some have hydroelectric power generation systems installed.
Dams are considered "installations containing dangerous forces" under international humanitarian law due to the massive impact of a possible destruction on the civilian population and the environment. Dam failures are comparatively rare, but can cause immense damage and loss of life when they occur. In 1975 the failure of the Banqiao Reservoir Dam and other dams in Henan Province, China caused more casualties than any other dam failure in history. The disaster killed an estimated 171,000 people and 11 million people lost their homes.
Common causes of dam failure include:
Sub-standard construction materials/techniques (Gleno Dam)
Spillway design error (near failure of Glen Canyon Dam, Oroville Dam, Walnut Grove Dam)
Lowering of dam crest height, which reduces spillway flow (South Fork Dam)
Geological instability caused by changes to water levels during filling or poor surveying (Malpasset Dam).
Sliding of a mountain into the reservoir (Vajont Dam – not a dam failure, but caused nearly the entire volume of the reservoir to be displaced and overtop the dam)
Poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava dam collapse)
Human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant)
Internal erosion or piping, especially in earthen dams (Teton Dam)
Climate-driven landscape instability (Rock-ice avalanches, Permafrost landslides, Debris flows, Outburst floods from glacial lakes and landslide-dammed lakes)
A notable case of deliberate dam breaching was the British Royal Air Force Dambusters raid on Germany in World War II (codenamed "Operation Chastise"), in which six German dams were selected to be breached in order to impact German infrastructure and manufacturing and power capabilities deriving from the Ruhr and Eder rivers. This raid later became the basis for several films.
Attacks on dams were restricted in Article 56 of the 1977 Protocol I amendment to the Geneva Conventions. Dams may not be lawfully attacked "if such attack may cause the release of dangerous forces from the works or installations and consequent severe losses among the civilian population", unless "it is used for other than its normal function and in regular, significant and direct support of military operations and if such attack is the only feasible way to terminate such support". Similar provisions apply to other sources of "dangerous forces", such as nuclear power plants.
Other cases include the Chinese bombing of multiple dams during Typhoon Nina (1975) in an attempt to drain them before their reservoirs overflowed. The typhoon produced what is now considered a 1-in-2,000-year flood, which few if any of these dams were designed to survive.
The Kakhovka Dam was destroyed in June 2023, during the Russian invasion of Ukraine.
Based on the advances in structural engineering, seismology and previous dam failures, it has become possible to predict, or in some cases to know with certainty, about future dam failures.