Sûreté des évacuateurs de crues de barrage. Enquête sur les projets d’évacuateurs de crues postérieurs à la publication des recommandations CFBR 2013 et enseignements – Comparaison aux pratiques internationales – Accidentologie récente des évacuateurs de crues

The analysis of project criteria adopted in France since 2012 is based on a large population of 63 VCA revision projects. The 2013 CFBR recommendations have been the basic reference for consulting engineering, with the exception of EDF which uses its own standard (for 25% of the projects studied) following the example of other operators in other other countries which also have their own standards (Hydro-Quebec, USACE, USBR, TVA, ETC.). The return periods of the exceptional flood respect almost all the CFBR 2013 recommendations. The VCA projects analyzed show the consideration of an extreme flood in 85% of the cases. The return periods for reaching the danger level respect the CFBR 2013 recommendations in 85% of the cases for Class A dams and in 66% of the Class A dams and in 66% of cases for all classes.In the analysis of regulations made through Bulletin 170, we did not see a distinction between new dams and dams in service, on this issue of spillway safety and sizing. However, Bulletin 170 is not comprehensive on international practices and does not indicate how the retrofitting of in-service dams is carried out. In Canada, the United States and Australia, the regulatory framework coexists with professional recommendations, which often provide more stringent criteria.The range of return periods for exceptional floods is very wide, from 100 years to more than 100,000 years (several countries). 100,000 years (several countries adopting the PMF). This range is significantly reduced if we are interested in reduced if we are only interested in European countries (between 1000 and 10 000 years), the CFBR recommendations and French regulations are in the middle of the distributions. The safety criteria associated with the exceptional flood vary significantly from one country to another , in particular for the availability of the gates (y/c in presence of ice jams) or thefreeboard.Ten countries (36%) prescribe (or recommend) to take into account an extreme flood, for large dams, in addition to the exceptional flood. The criteria associated with the extreme flood are relatively homogeneous: in an extreme flood situation, the dam can suffer from disorders, but without but without its ultimate safety being called into question. The practice of a double verification of exceptional and extreme floods is therefore not in the majority, but this is to be put into perspective because some countries adopt a very high exceptional flood (PMF) which which covers the extreme floods.The analysis of the accidentology covered 36 accidents and major incidents that have occurred since 2000, including 9 cases of 2000, including 9 cases in France. This abundant accidentology shows the importance of safety of spillways in the safety of a dam. The hydrological and hydraulic design is involved (or suspected) in about half of the cases, sometimes half of the cases, sometimes concomitantly with other factors. The lessons learned from these case studies also allow to highlight the other key subjects, decisive factors in the failure decisive factors in the failure scenario or in the ultimate resistance of the dam. Most of these topics of these topics are addressed in the 2013 CFBR Recommendations, but some may deserve new developments merit further development and/or revision of the recommendations:- Structural strength of spillways;- Rock erosion resistance downstream of concrete dams;- The resistance to flooding erosion of embankment dams;- Kinetics of events VS the time required for decisions and actions;- Reliability of the control system;- Safety in operation;- The update of the "Flood Assessment Recommendations" section of the 2013 CFBR recommendations of the CFBR 2013, knowing that the quality of the hydrological studies used as input data is essential;- Enriching the chapter "Spillway sizing for floating bodies of the CFBR 2013 recommendations;- To propose a global functional approach of the passage of the floods, by distinguishing the sub-functions of control of the flow to be discharged, transfer of the flow to be discharged and downstream dissipation of the power of the discharged flow, and the control of erosion. of erosion.Finally, the work of our WG has highlighted the need to clarify and stabilize the terminology.

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