A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments. Most dams have a section called a spillway or weir over which, 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. In 2012 a dam in northern state of Rio de Janeiro, Brazil failed forcing thousands of people from homes. The water broke through the dam protecting the town of Campos de Goytacazes. Officials described the situation as race against time to evacuate people before the area becomes flooded. Since this incident, the Brazil government has step up early warning systems to ensure people evacuate before floods strike. 
Main causes of dam failure
Common causes of dam failure include:
- Sub-standard construction materials/techniques (Gleno Dam)
- Spillway design error (South Fork Dam, near failure of Glen Canyon 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 exactly a dam failure, but caused nearly the entire volume of said reservoir to be displaced and overtop the dam)
- Poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava dam collapse)
- Extreme inflow (Shakidor Dam)
- Human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant)
- Internal erosion, especially in earthen dams (Teton Dam)
Deliberate dam failure
A notable case of deliberate dam failure (prior to the Humanitarian Law rulings) was the British Royal Air Force Dambusters raid on Germany in World War II (codenamed "Operation Chastise"), in which three German dams were selected to be breached in order to impact on German infrastructure and manufacturing and power capabilities deriving from the Ruhr and Eder rivers. This raid later became the basis for several films.
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-2000 years flood, which few if any of these dams were designed to survive.
List of major dam failures
|Marib Dam||575||Sheba, Yemen||Unknown causes, possibly neglect. The consequent failure of the irrigation system provoked the migration of up to 50,000 people from Yemen.|
|Puentes Dam||1802||Lorca, Spain||608||1,800 houses and 40,000 trees destroyed.|
|Bilberry reservoir||1852||Holme Valley, United Kingdom||81||Failed due to heavy rain.|
|Dale Dike Reservoir||1864||South Yorkshire, United Kingdom||244||Defective construction, small leak in wall grew until dam failed. More than 600 houses were damaged or destroyed.|
|Mill River Dam||1874||Williamsburg, United States||139||Lax regulations and cost cutting lead to an insufficient design, which fell apart when the reservoir was full. 600 million gallons of water were released, wiping out 4 towns and making national headlines. This dam break lead to increased regulation of dam construction.|
|South Fork Dam||1889||Johnstown, United States||2,209||Blamed locally on poor maintenance by owners; court deemed it an "Act of God". Followed exceptionally heavy rainfall. Caused Johnstown flood. 1,600 homes were destroyed.|
|Walnut Grove Dam||1890||Wickenburg, United States||100||Heavy snow and rain following public calls by the dam's chief engineer to strengthen the earthen structure.|
|Gohna Lake dam||1894||Garhwal, India||1||Failure of a landslide dam. Authorities had been able to evacuate the valley.|
|McDonald Dam||1900||Texas, United States||8||Extreme current caused failure.|
|Hauser Dam||1908||Helena, United States||0||Heavy flooding coupled with poor foundation quality. Workers managed to warn people downstream.|
|Austin Dam||1911||Austin, United States||78||Poor design, use of dynamite to remedy structural problems. Destroyed paper mill and much of the town of Austin.|
|Desná Dam||1916||Desná, Austria-Hungary (now Czech Republic)||62||Construction flaws caused the dam failure.|
|Lake Toxaway Dam||1916||Transylvania County, United States||0||Heavy rains caused the dam to give way. Dam was later rebuilt in the 1960s|
|Sweetwater Dam||1916||San Diego County, United States||0||Over-topped from flooding.|
|Lower Otay Dam||1916||San Diego County, United States||14||Over-topped from flooding.|
|Tigra Dam||1917||Gwalior, India||1,000||Failed due to water infiltrating through foundation. Possibly more fatalities.|
|Gleno Dam||1923||Province of Bergamo, Italy||356||Poor construction and design.|
|Llyn Eigiau dam and Coedty reservoir||1925||Dolgarrog, United Kingdom||17||The outflow from Llyn Eigiau destroyed Coedty reservoir. Contractor blamed cost-cutting in construction but 25" of rain had fallen in preceding 5 days.|
|St. Francis Dam||1928||Santa Clarita, United States||600||Geological instability of canyon wall that could not have been detected with available technology of the time.|
|Secondary Dam of Sella Zerbino||1935||Molare, Italy||111||Geological unstable base combined with flood.|
|Nant-y-Gro dam||1942||Elan Valley, United Kingdom||0||Destroyed during preparation for Operation Chastise in World War II.|
|Edersee Dam||1943||Ruhr, Germany||70||Destroyed by bombing during Operation Chastise in World War II. Widespread destruction.|
|Möhne Dam||1943||Ruhr, Germany||1,579||Destroyed by bombing during Operation Chastise in World War II. 11 factories were destroyed, 114 seriously damaged.|
|Tangiwai disaster||1953||Whangaehu River, New Zealand||151||Failure of Mount Ruapehu's crater lake.|
|Vega de Tera||1959||Ribadelago, Spain||144||According to dam workers testimonies, the grounds had serious structural deficiencies due to poor construction. On the night of January 9, a 150 meters long portion of the contention wall collapsed letting out nearly 8 million cubic meters of stored water. |
|Malpasset dam||1959||Côte d'Azur, France||423||Geological fault possibly enhanced by explosives work during construction; initial geo-study was not thorough. Two villages were destroyed.|
|Kurenivka mudslide||1961-03-13||Kiev, Ukraine||1,500||Caused by heavy rains with up to 2,000 fatalities.|
|Panshet Dam||1961||Pune, India||1,000||Dam wall burst due to pressue of accumulated rain water.|
|Baldwin Hills Reservoir||1963||Los Angeles, United States||5||Subsidence caused by over-exploitation of local oil field. 277 homes destroyed.|
|Spaulding Pond Dam (Mohegan Park)||1963||Norwich, United States||6||More than $6 million estimated damages.|
|Vajont Dam||1963||Monte Toc, Italy||2,000||Strictly not a dam failure, since the dam structure did not collapse and is still standing. Filling the reservoir caused geological failure in valley wall, leading to 110 km/h landslide into the lake; water escaped in a seiche over the top of dam. Valley had been incorrectly assessed stable. Several villages completely wiped out.|
|Swift Dam||1964-06-10||Montana, United States||28||Caused by heavy rains.|
|Mina Plakalnitsa||1966||Vratsa, Bulgaria||107||A tailings dam at Plakalnitsa copper mine near the city of Vratsa failed. A total 450,000 cu m of mud and water inundated Vratsa and the nearby village of Zgorigrad, which suffered widespread damage. The official death toll is 107, but the unofficial estimate is around 500 killed.|
|Sempor Dam||1967||Central Java Province, Republic of Indonesia||2,000||Flash floods over-topped the dam during construction.|
|Certej dam failure||1971||Certej Mine, Romania||89||A tailings dam built too tall collapsed, flooding Certeju de Sus with toxic tailings.|
|Buffalo Creek Flood||1972||West Virginia, United States||125||Unstable loose constructed dam created by local coal mining company, collapsed in heavy rain. 1,121 injured, 507 houses destroyed, over 4,000 left homeless.|
|Canyon Lake Dam||1972||South Dakota, United States||238||Flooding, dam outlets clogged with debris. 3,057 injuries, over 1,335 homes and 5,000 automobiles destroyed.|
|Banqiao and Shimantan Dams||1975||Zhumadian, China||171,000||Extreme rainfall, beyond the planned design capability of the dam, dumped on China by Typhoon Nina. 11 million people lost their homes. Worst dam failure.|
|Teton Dam||1976||Idaho, United States||11||Water leakage through earthen wall, leading to dam failure. 13,000 head of cattle died.|
|Laurel Run Dam||1977||Johnstown, United States||40||Heavy rainfall and flooding that over-topped the dam. Six other dams failed the same day, killing five people.|
|Kelly Barnes Dam||1977||Georgia, United States||39||Unknown, possibly design error as dam was raised several times by owners to improve power generation.|
|Machchu-2 Dam||1979||Morbi, India||5,000||Heavy rain and flooding beyond spillway capacity. Old estimates were 1,800-25,000 but a recent book by Sandersara & Wooten reduce the bracket to 5,000-10,000.|
|Wadi Qattara Dam||1979||Benghazi, Libya||0||Flooding beyond discharge and storage capacity damaged the main dam and destroyed the secondary dam in the scheme.|
|Lawn Lake Dam||1982||Rocky Mountain National Park, United States||3||Outlet pipe erosion; dam under-maintained due to location.|
|Tous Dam||1982||Valencia, Spain||25||Heavy flooding coupled with poor quality of the dam wall, lack of qualified staff and negligence of a warning of heavy rain in the area. On the next day, newspapers reported possibly 40 fatalities and 25 disappeared but in the coming days the count went down to 8 or 9. One year later, LaVanguardia spoke of 25.|
|Val di Stava dam||1985||Tesero, Italy||268||Poor maintenance and low margin for error in design; outlet pipes failed leading to pressure on dam.|
|Upriver Dam||1986||Washington state, United States||0||Lightning struck power system, turbines shut down. Water rose behind dam while trying to restart. Backup power systems failed, could not raise spillway gates in time. Dam overtopped(rebuilt).|
|Kantale Dam||1986-04-20||Kantale, Sri Lanka||180||Poor maintenance, leakage, and consequent failure. Destroyed over 1600 houses and 2000 acres of paddy fields.|
|Peruća Dam detonation||1993||Split-Dalmatia County, Croatia||0||Not strictly a dam failure as there was a detonation of pre-positioned explosives by retreating Serb Forces.|
|Merriespruit tailings dam||1994||Free State, South Africa||17||Dam failed after a heavy thunderstorm. The dam was in an unacceptable condition prior to failure. Widespread devastation and environmental damage.|
|Saguenay Flood||1996||Quebec, Canada||10||Problems started after two weeks of constant rain, which severely engorged soils, rivers and reservoirs. Post-flood enquiries discovered that the network of dikes and dams protecting the city was poorly maintained.|
|Meadow Pond Dam||1996||New Hampshire, United States||1||Design and construction deficiencies resulted in failure in heavy icing conditions.|
|Opuha Dam||1997||Canterbury, New Zealand||0||Heavy rain during construction caused failure, dam was later completed.|
|Doñana disaster||1998-04-25||Andalusia, Spain||0||Over-steepened dam failed by sliding on weak clay foundation, releasing 4–5 million cubic metres of acidic mine tailings into the River Agrio, a tributary of the River Guadiamar, which is the main water source for the Doñana National Park, a UNESCO World Heritage Site.|
|Shihgang Dam||1999-09-21||Taiwan||0||Caused by damage sustained during the 921 earthquake.|
|Martin County coal slurry spill||2000-10-11||Martin County, United States||0||Failure of a coal slurry impoundment. The water supply for over 27,000 residents was contaminated. The spill was 30 times larger than the Exxon Valdez oil spill and one of the worst environmental disasters ever in the southeastern United States|
|Vodní nádrž Soběnov||2002||Soběnov, Czech Republic||0||Extreme rainfall during the 2002 European floods.|
|Zeyzoun Dam||2002||Zeyzoun, Syria||22||2,000 induviduals displaced and over 10,000 directly affected.|
|Ringdijk Groot-Mijdrecht (nl)||2003||Wilnis, Netherlands||0||Peat dam became lighter than water during droughts and floated away. Around 1,500 residents had to be evacuated.|
|Hope Mills Dam||2003-05||North Carolina, United States||0||Caused by heavy rains. 1,600 people evacuated.|
|Silver Lake Dam||2003-05-14||Michigan, United States||0||Heavy rains caused earthen dam and bank to wash away. 1,800 people evacuated.|
|Big Bay Dam||2004||Mississippi, United States||0||A small hole in the dam grew and eventually led to failure. 104 buildings damaged or destroyed.|
|Camará Dam||2004-06-17||Paraiba, Brazil||3||Poor maintenance. 3000 people homeless. A second failure happened 11 days after.|
|Shakidor Dam||2005||Pasni, Pakistan||70||Sudden and extreme flooding caused by abnormally severe rain.|
|Taum Sauk reservoir||2005||Lesterville, United States||0||Computer/operator error; gauges intended to mark dam full were not respected; dam continued to fill. Minor leakages had also weakened the wall through piping. The dam of the lower reservoir withstood the onslaught of the flood.|
|Campos Novos Dam||2006||Campos Novos, Brazil||0||Tunnel collapse.|
|Gusau Dam||2006||Gusau, Nigeria||40||Heavy flooding. Approximately 500 homes were destroyed, displacing 1,000 people.|
|Ka Loko Dam||2006||Kauai, Hawaii||7||Heavy rain and flooding. Several possible specific factors to include poor maintenance, lack of inspection and illegal modifications.|
|Lake Delton||2008-06-09||Lake Delton, United States||0||Failure due to June 2008 Midwest floods.|
|Koshi Barrage||2008||Koshi Zone, Nepal||250||Heavy rain. The flood affected over 2.3 million people in the northern part of Bihar.|
|Kingston Fossil Plant coal fly ash slurry spill||2008-12-22||Roane County, United States||0||Failure of a fly ash slurry pond.|
|Algodões Dam||2009-05-27||Piaui, Brazil||7||Heavy rain. 80 people injured, 2000 homeless.|
|Sayano–Shushenskaya Dam||2009-08-17||Sayanogorsk, Russia||75||Collapses when turbine 2 broke apart violently, flooding the turbine hall and causing the ceiling to collapse.|
|Situ Gintung Dam||2009||Tangerang, Indonesia||98||Poor maintenance and heavy monsoon rain.|
|Kyzyl-Agash Dam||2010||Qyzylaghash, Kazakhstan||43||Heavy rain and snowmelt. 300 people were injured and over 1000 evacuated from the village.|
|Hope Mills Dam||2010||North Carolina, United States||0||Sinkhole caused dam failure. Second failure of the dam, will be replaced.|
|Testalinda Dam||2010-06-13||Oliver, Canada||0||Heavy Rain, low maintenance. Destroyed at least 5 homes. Buried Highway 97.|
|Delhi Dam||2010-07-24||Iowa, United States||0||Heavy rain, flooding. Around 8,000 people had to be evacuated.|
|Niedow Dam||2010-08-07||Lower Silesian Voivodeship, Poland||1||Heavy rain, over-topped from flooding.|
|Ajka alumina plant accident||2010-10-04||Ajka, Hungary||10||Failure of concrete impound wall on alumina plant tailings dam. One million cubic meters of red mud contaminated a large area, within days the mud had reached the Danube.|
|Kenmare Resources tailings dam||2010-10-08||Topuito, Mozambique||1||Failure of tailings dam at titanium mine. 300 homes had been rebuilt.|
|Fujinuma Dam||2011-03-11||Sukagawa, Japan||8||Failed after 2011 Tōhoku earthquake. 7 dead and 1 unknown. Japanese authority says dam failure caused by earthquake which has death toll is not reported world-wide since 1930.|
|Campos dos Goytacazes dam||2012-01-04||Campos dos Goytacazes, Brazil||0||Failed after a period of flooding. 4000 people displaced.|
|Ivanovo Dam||2012-02-06||Biser, Bulgaria||8||Failed after a period of heavy snowmelt. A crack in the dam went un-repaired for years. Eight people killed and several communities flooded.|
|Köprü Dam||2012-02-24||Adana Province, Turkey||10||A gate in the diversion tunnel broke after a period of heavy rain during the reservoir's first filing. The accident killed ten workers.|
|Tokwe Mukorsi Dam||2014-02-04||Masvingo Province, Zimbabwe||0||Downstream slope failure on a 90.3 m (296 ft) tall embankment dam, possibly as the reservoir was being filled. Residents evacuated upstream.|
- Osnos, Evan. "Faust, China, and Nuclear Power," The New Yorker, Wednesday October 12, 2011. Retrieved at http://www.newyorker.com/online/blogs/evanosnos/2011/10/faust-china-and-nuclear-power.html on October 12, 2011
- Brazil dam burst forces thousands from homes. (2012, January 5). BBC. Retrieved from, <http://www.bbc.co.uk/news/world-latin-america-16426732>
- La rotura del pantano de Puentes
- "Arizona's 1890 dam disaster killed more than 100 people" The Daily Courier. http://dcourier.com/main.asp?SectionID=1&SubSectionID=1&ArticleID=48987 Retrieved 30 January 2015.
- 40 años de la tragedia de Ribadelago, en la que murieron 144 personas (Spanish)
- July 12, 1961 - Lest We Forget
- Wohl, Ellen (2013). Mountain Rivers Revisited. John Wiley & Sons. p. 338. ISBN 1118671562.
- "Certej 1971, tragedia uitată a 89 de vieţi îngropate sub 300 de mii de metri cubi de nămol". Adevărul. 31 August 2013. Retrieved 30 March 2013.
- "No One Had a Tongue to Speak". 12 May 2014. Retrieved 12 May 2014.
- "Syria - Collapse of Dam/floods OCHA Situation Report No. 4". ReliefWeb. Retrieved 26 February 2012.
- Chanson, Hubert Chanson Hubert (2009). "Embankment Overflow Protection Systems and Earth Dam Spillways". Dams: Impacts, Stability and Design.
- "Kauai Dam Breach Killed 7 People Five Years Ago, But Criminal Charges Against Dam Owner Still Pending." Hawaii Reporter. http://www.hawaiireporter.com/kauai-dam-breach-killed-7-five-years-ago-but-criminal-charges-still-pending/123 Retrieved 24 July 2013.
- "Breaching of the Algodões dam and the threat of mega-projects". Movement of Dam Affected People. 29 May 2009. Retrieved 6 January 2012.
- Ereignisanalyse Hochwasser im August und September 2010 und im Januar 2011 in Sachsen, chapter 9 (pdf, 16,34 MB)
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- "Bulgarian Dam Collapsed over Unrepaired Crack since 2003". NoVinite. 6 February 2012. Retrieved 26 February 2012.
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- A list of dam failures and incidents in the United States Dam Safety.org
- Chronology of major tailings dam failures from 1960 WISE Uranium Project
- Chanson, H. (2009) Application of the Method of Characteristics to the Dam Break Wave Problem Journal of Hydraulic Research, IAHR, Vol. 47, No. 1, pp. 41–49 doi:10.3826/jhr.2009.2865 (ISSN 0022-1686). Available as a pdf at 
- Dam Failure and Flood Event Case History Compilation Bureau of Reclamation