The combination of a high tide (coefficient 106), swift current of the Seine (1600 m³/s) and waves generated by multiple ships caused a low concrete-block flood wall encircling an embankment to break up along 2 km, lowering the embankment’s protection threshold by 45 cm. Flaws were found in the flood wall’s design. Realising the risk of flooding to nearby homes, the operator alerted the neighbouring communities and informed the department in charge of inspecting hydraulic structures and the inspection authorities for classified facilities. It also began performing emergency work.

The low wall, considered by the manager to be the flood protection system’s crest level, will have to be completely rebuilt before the next spring tides because of the risk of flooding. The hydraulic structure inspection department and the inspection authorities for classified facilities authorised the operator to perform emergency work without first having to obtain the immediate approval of an accredited engineering and design firm. It nevertheless recommended that the operator contact such a firm as quickly as possible because the wall’s rebuilding (which includes placing reinforced concrete anchoring blocks inside the structure) is a substantial structural change that must be carried out by an authorised body.