Dam Failure

Primary reference(s)

ICOLD, 2015. Definition of a Large Dam. International Commission on Large Dams (ICOLD). Accessed 8 November 2020.

Additional scientific description

Dams are commonly categorised by a wide range of factors such as composition, height, and reservoir volume. Dams are typically constructed of earth, rock, concrete or tailings (chaff) from mining operations. As a function of upstream topography, even a small dam can impound or detain many acre-feet of millions of gallons of water (FEMA, 2017). The collapse or movement leading to a break in the dam, could produce life-threatening flood situations due to the high velocities and large volumes of water involved. In the event of a dam failure, the potential energy of water stored behind the dam can cause significant damage to property and livelihoods, as well as injuries and loss of life for people downstream of the dam (FEMA, 2017).

Two summary examples of dam failures follow:

• Brumadinho dam disaster Brazil 2019. On 25 January 2019, Córrego do Feijão’s tailing dam at Brumadinho city breached, leading to at least 12 million cubic metres of tailing spread into Paraopeba River and the surrounding area, leaving more than 250 people dead and many missing, with major environmental impacts on the downstream catchment (Cambridge and Shaw, 2019; Thompson et al., 2020). This was the fifth tailings dam disaster to have occurred in the same region in an 18-year period and is considered the worst documented tailings dam failure to have occurred in the past 30 to 40 years. The failure at Brumadinho showed geotechnical similarities to that at Fundao in 2015, with the characteristic of all foundation zones predisposing the facility to an increased risk of basal liquefaction under increasing stress. Upstream construction, as well as management commitment to quality control and inspection and monitoring during operation are potentially considered for the failure of the Brumadinho dam.
• Ajka Red Sludge Reservoir. On 4 October 2010, the retaining wall of a caustic waste reservoir at the Ajka alumina plant near Kolontar, Hungary, collapsed releasing more than one million cubic metres of highly alkaline sludge containing toxic metals. The waste material flooded several nearby villages, resulting in 10 fatalities, 123 injured people, damage to buildings, and significant ecological and environmental impacts. Reports concluded that a check on the reservoirs stability and statics had not been performed by the relevant authorities (NDGDM, 2010).

A review of failure mode analysis and implications for current and future resilience of flood protection infrastructure in the United States has been undertaken (Primary and Secondary Causes of Dam Failure in the US, no date). Dam failures are classified by date, location, dam type, primary and secondary root causes, cost in year of incident, damage type, and fatalities.

The International Commission on Large Dams (ICOLD) is an international non-governmental organisation dedicated to sharing professional information and knowledge of the design, construction, maintenance, and impact of large dams. ICOLD has 100 member national committees and over 10,000 individual members, (ICOLD, no date). ICOLD has created a World Register of Dams. This is a global database on dams, established based on the national inventories sent by member countries of ICOLD. The register is continuously updated and includes information on more than 55,000 dams. In addition to the dam register, ICOLD has developed a technical dictionary. Between 2000 and 2009, more than 200 notable dam failures happened worldwide (Jonkman and Vrijling, 2008).

Metrics and numeric limits

Not identified.

Examples of drivers, outcomes and risk management

Dam failure is likely to occur due to seepage and internal erosion, poor foundation conditions, overtopping, static and seismic instability and for other reasons such as subsidence, structural issues, external erosion and slope instability (Lyu et al., 2019).

Dam safety agencies have generally adopted a common tiered hazard classification structure including Low, Significant, and High hazard potential classifications. Dam safety engineers commonly use the hazard potential classification system as a prioritisation tool to focus attention on those dams with the greatest potential consequences of failure. Two components are used to determine dam failure risk profiles: likelihood of failure and consequences of failure. Hazard classifications are defined as follows (FEMA, 2017):

• The consequences of a low hazard potential dam failure should result in no probable loss of human life and low economic and/or environment losses.
• The consequences of a significant hazard potential dam failure should result in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns.
• The consequences of a high hazard potential dam failure will probably cause loss of human life.

Risk creep also known as hazard creep is a term used to describe the gradual increase in anticipated consequences of a dam failure due to infrastructure development either along the drainage below a dam or within the reservoir area upstream. Although the physical condition of the dam may not change, hazard creep can result in an immediate adverse impact on the overall risk profile of a dam because the consequence component has increased. For example, new residential development within the dam breach floodplain could raise the status of a dam from one with a low hazard potential to one with significant or high hazard potential. Hazard creep can require costly dam safety modifications to address design deficiencies, such as to increase spill way capacity to safely route the probable maximum flood (for high hazard potential dams) (FEMA, 2017).

Following recent dam failure disasters, many countries put safety first and invest in prevention largely using Dam Safety Laws. This includes applying the UNECE’s safety standards ‘Safety Guidelines and Good Practices for Tailings Management facilities’ (UNECE, 2016). Such guidelines, developed by the Joint Expert Group on Water and Industrial Accidents under UNECE’s Industrial Accidents Convention and Water Convention, provide authorities with recommendations for practical applications to limit accidents and the severity of their consequences (UNECE, 2016).

The Conference of the Parties to the United Nations Economic Commission for Europe Industrial Accidents Convention sets the future direction for technological disaster risk reduction towards 2030 (UNECE, 2018).