During quarterly testing of a dam’s mobile instrumentation used to regulate SEINE River flow rates, a link in the articulated roller chain that allowed raising the left valve did not release properly from the upper motor pinion gear. The chain wrapped around this gear until a point of blocking the lift movement. The motor torque limiter activated and the installation short-circuited. The torque detector located in back of the reduction gear failed to function. Moreover, subsequent to a repair performed on 4 October, the opening on the dam’s central valve was decreased to 4 m so as not to damage the storage chamber of the articulated roller chain when raising the valve. The maximum flooding flow rate accommodated by the facility in its present state was limited (955 m³/s) yet remained above the thousand-year flood rate (800 m³/s). To withstand an extreme event, the dam operator had developed a crane-assisted left valve manoeuvre.

The left valve was locked out in the closed position. A cofferdam was built upstream of this valve; the system was repaired and modified based on the conclusions of an expert appraisal. The storage chamber on the central valve’s articulated roller chain was adapted to create a full-sized opening. The stainless steel articulated roller chains had been installed in 2009-2010 to replace steel chains, whose links had stiffened due to grease accumulation. The operator completed the stainless steel assembly by adding a lubrication system servo-controlled to the motor pinion gear rotation.