Le risque de rupture de barrage

Commissariat général au développement durableJun 3, 2019

Un barrage est un ouvrage établi en travers du lit d’un cours d’eau, retenant ou pouvant retenir de l’eau. Une rupture de barrage correspond à une destruction partielle ou totale de l’ouvrage et entraîne la formation d’une onde de submersion se traduisant par une élévation brutale du niveau de l’eau à l’aval, voire un gigantesque torrent. Ce type d’événement peut avoir des conséquences catastrophiques pour la population située en aval du barrage. Deux accidents de rupture de barrages sont survenus en France : en 1895, à Bouzey dans les Vosges et en 1959 à Malpasset dans le Var. En 2017, 2163 barrages sont implantés sur le territoire.

A dam is a structure built across a river course that retains or can retain water. A dam failure corresponds to partial or total destruction of the structure and results in a flood wave causing a sudden rise in water level downstream, or even a giant torrent. This type of event can have catastrophic consequences for the population downstream of the dam. Two dam failure accidents have occurred in France: in 1895 at Bouzey in the Vosges and in 1959 at Malpasset in the Var. In 2017, 2163 dams were located in the country.

2 chapters

Types of dams
Dam functions
• Dams can serve the following primary purposes: • electricity generation, • water flow regulation (flood control, low-flow support), • crop irrigation, • water supply to cities, • water supply for industry, • recreational interest (water retention), • fire prevention (water reserve). A particular use is also being developed: reservoirs for artificial snow production.
Dam classification
• Dams and levees are classified into 3 categories: A, B, or C under decree 2015-526 of May 12, 2015. This classification depends on the structure's height and retained volume. The least significant dams are classified C with a minimum height of 2 meters. The most significant are classified A with a height of 20 meters or more. Class B dams are at least 10 meters tall. There are 317 class A dams, 324 class B dams, and 1522 class C dams.
Regulatory framework
• Dams higher than 20 meters with a capacity exceeding 15 million m³ are subject to an emergency response plan. This plan specifies the modalities for population alert, possible evacuation, and emergency organization in the event of dam failure. Additionally, class A, B, and C dams are subject to a hazard study, surveillance report, in-depth technical inspections, and an auscultation report, following the frequencies set by decree no. 2015-526: see the dedicated section on the Ministry of Ecological and Inclusive Transition website
Events and accidents at dams
Reporting obligation
Dam operators are required to report events occurring on these structures. Events significant for hydraulic safety (EISH) and precursory events for hydraulic safety (PSH) must be reported to the prefect by the operator or owner of the structure, as required by article R214-125 of the environmental code.
EISH events
• EISH events concern: • threats to people's safety (accident, endangerment, or risk), • damage to property (including river beds, banks, and reservoirs) or hydraulic structures, • for a dam, any modification of its operation or hydraulic characteristics (water level, etc.).
PSH events
• PSH events concern malfunctions linked to failures of "safety barriers" identified in the hazard study that could lead to loss of safety functions such as "retaining water," "controlling upstream water level" or "controlling downstream water release." • According to their increasing severity, state services responsible for dam control (DREAL) assign a color (yellow, orange, or red) to declared EISH events.
Event statistics
• The ARIA database of BARPI (see Technological accidents) records 445 events on dams between 1992 and end of 2017. 72% of events with known origins were caused by material defects, 17% by human intervention, and the remaining 11% by various causes (loss of process control, latent hazards, malice, external aggression). In 2016, BARPI recorded 36 EISH on levees (notably linked to the Loing and Seine floods) and dams. Among events on dams, 60% resulted in modification of structure characteristics, 35% involved non-compliance with operating procedures, and 5% posed danger to people.

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