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.
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).
- 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 (possibly neglect)|
|Pantano de Puentes||1802||Lorca, Spain||608||1800 houses and 40000 trees destroyed|
|Dale Dike Reservoir||1864||South Yorkshire, England, United Kingdom||Defective construction, small leak in wall grew until dam failed.|
|Mill River Dam||1874||Williamsburg, Massachusetts, 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, Pennsylvania, United States||Blamed locally on poor maintenance by owners; court deemed it an "Act of God". Followed exceptionally heavy rainfall. Caused Johnstown flood.|
|Walnut Grove Dam||1890||Wickenburg, Arizona Territory, United States||Heavy snow and rain following public calls by the dam's chief engineer to strengthen the earthen structure.|
|McDonald Dam||1900||Texas, United States||Extreme current caused failure.|
|Hauser Dam||1908||Helena, Montana, United States||Heavy flooding coupled with poor foundation quality|
|Austin Dam||1911||Austin, Pennsylvania, United States||Poor design, use of dynamite to remedy structural problems.|
|Desná Dam||1916||Desná, Austria-Hungary (now Czech Republic)||62||Construction flaws caused the dam failure|
|Lake Toxaway Dam||1916||Transylvania County, North Carolina||0||Heavy rains caused the dam to give way. Dam was later rebuilt in the 1960s|
|Sweetwater Dam||1916||San Diego County, California||Over-topped from flooding|
|Lower Otay Dam||1916||San Diego County, California||40||Over-topped from flooding|
|Gleno Dam||1923||Province of Bergamo, Italy||356||Poor construction and design|
|Llyn Eigiau dam and the outflow also destroyed Coedty reservoir dam.||1925||Dolgarrog, North Wales, UK||10<16||Contractor blamed cost-cutting in construction but 25" of rain had fallen in preceding 5 days. This was the last dam failure to cause death in the UK to date (2010).|
|St. Francis Dam||1928||Santa Clarita, California, Los Angeles County, United States||600||Geological instability of canyon wall that could not have been detected with available technology of the time, combined with human error that assessed developing cracks as "normal" for a dam of that type.|
|Nanty Gro Reservoir in Wales||1942||Nanty Gro Valley, Wales||Destroyed during preparation for Operation Chastise in World War II.|
|Eder, Möhne Dams||1943||Eder Valley, Ruhr, Germany||47<100||Destroyed by bombing during Operation Chastise in World War II.|
|Vega de Tera||1959||Ribadelago, Spain||144 deaths|
|Malpasset||1959||Côte d'Azur, France||400||Geological fault possibly enhanced by explosives work during construction; initial geo-study was not thorough.|
|Baldwin Hills Reservoir||1963||Los Angeles, California, United States||3||Subsidence caused by over-exploitation of local oil field|
|Spaulding Pond Dam (Mohegan Park)||1963||Norwich, Connecticut, United States||6||more than $6 million estimated damages|
|Vajont Dam||1963||Italy||2000||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.|
|Mina Plakalnitsa, (Vratsa)||1966||Vratsa, Bulgaria||500?||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. |
|Buffalo Creek Flood||1972||West Virginia, United States||125||Unstable loose constructed dam created by local coal mining company, collapsed in heavy rain|
|Canyon Lake Dam||1972||South Dakota, United States||Flooding, dam outlets flooded with debris.|
|Banqiao and Shimantan Dams||1975||China||100,000 or more||Extreme rainfall beyond the planned design capability of the dam. Worst dam failure.|
|Teton Dam||1976||Idaho, United States||11||Water leakage through earthen wall, leading to dam failure.|
|Laurel Run Dam||1977||Johnstown, Pennsylvania, United States||Heavy rainfall and flooding that over-topped the dam.|
|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, Gujarat, India||1,800<15,000||Heavy rain and flooding beyond spillway capacity.|
|Wadi Qattara Dam||1979||Benghazi, Libya||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||between 30-40|
|Val di Stava Dam collapse||1985||Italy||Poor maintenance and low margin for error in design; outlet pipes failed leading to pressure on dam.|
|Upriver Dam||1986||Washington state, United States||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).|
|Peruća Dam detonation||1993||Croatia||Not strictly a dam failure as there was a detonation of pre-positioned explosives by retreating Serb Forces.|
|Saguenay Flood||1996||Quebec, Canada||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||Design and construction deficiencies resulted in failure in heavy icing conditions|
|Opuha Dam||1997||New Zealand||Heavy rain during construction caused failure, dam was later completed|
|Aznalcollar Mine Tailings Dam / The Doñana disaster||25 April 1998||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.|
|Vodní nádrž Soběnov||2002||Soběnov, Czech Republic||Extreme rainfall during the 2002 European floods|
|Zeyzoun Dam||2002||Zeyzoun, Syria||Failed 4 June 2002, killing 22 and affecting 10,000.|
|Ringdijk Groot-Mijdrecht||2003||Wilnis, Netherlands||Peat dam became lighter than water during droughts and floated away|
|Hope Mills Dam||2003||North Carolina, United States||Heavy rains caused earthen dam and bank to wash away|
|Big Bay Dam||2004||Mississippi, United States||A small hole in the dam grew and eventually led to failure.|
|Shakidor Dam||2005||Pakistan||70||Sudden and extreme flooding caused by abnormally severe rain|
|Taum Sauk reservoir||2005||Lesterville, Missouri, United States||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.|
|Campos Novos Dam||2006||Campos Novos, Brazil||Tunnel collapse|
|Gusau Dam||2006||Gusau, Nigeria||Heavy flooding|
|Ka Loko Dam||2006||Kauai, Hawaii||Heavy rain and flooding. Several possible specific factors to include poor maintenance, lack of inspection and illegal modifications.|
|Lake Delton||9 June 2008||Lake Delton, Wisconsin||Failure due to June 2008 Midwest floods.|
|Koshi Barrage||2008||Kusha[disambiguation needed], Nepal||Heavy rain|
|Algodões Dam||27 May 2009||Piau, Brazil||Heavy rain|
|Situ Gintung Dam||2009||Tangerang, Indonesia||Poor maintenance and heavy monsoon rain|
|Kyzyl-Agash Dam||2010||Kazakhstan||Heavy rain and snowmelt|
|Hope Mills Dam||2010||North Carolina, United States||Sinkhole caused dam failure|
|Delhi Dam||July 24, 2010||Iowa, United States||Heavy rain, flooding.|
|Niedow Dam||August 7, 2010||Lower Silesian Voivodeship, Poland||Heavy rain, over-topped from flooding|
|Ajka alumina plant accident||October 4, 2010||Hungary||10||Failure of concrete impound wall on alumina plant tailings dam.|
|Kenmare Resources tailings dam||October 8, 2010||Mozambique||Failure of tailings dam at titanium mine.|
|Fujinuma Dam||March 11, 2011||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.|
|Dam in Campos de Goytacazes, Brazil||January 4, 2012||Rio de Janeiro State, Brazil||Failed after a period of flooding.|
|Ivanovo Dam||February 6, 2012||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||February 24, 2012||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.|
- 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
- La rotura del pantano de Puentes
- 40 años de la tragedia de Ribadelago, en la que murieron 144 personas (Spanish)
- "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.
- "Breaching of the Algodões dam and the threat of mega-projects". Movement of Dam Affected People. 29 May 2009. Retrieved 6 January 2012.
- http://www.kahoku.co.jp/spe/spe_sys1072/20110518_01.htm (JPN)
- "Brazil dam burst forces thousands from homes". BBC. 5 January 2012. Retrieved 6 January 2012.
- "Bulgarian Dam Collapsed over Unrepaired Crack since 2003". NoVinite. 6 February 2012. Retrieved 26 February 2012.
- "Cover Kozan Dam Explosion" (in Turkish). Haberler. 8 March 2012. Retrieved 11 March 2012.
- "Holding Ozaltin conscience" (in Turkish). Emlak Kulisi. 10 March 2012. Retrieved 11 March 2012.
- 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 
See also