At 3:15 a.m., during a flood, the 3 gates of a navigation dam on the Moselle River were placed in the high position. The reservoir’s level upstream of the dam rose to 43 cm above the structure’s upper operating level. The flow downstream decreased significantly. At 3:30 a.m., the level reached the emergency PLC’s trip threshold, which initiated a decrease in the impoundment and triggered an alarm to the on-call technician who arrived on site at 4:00 a.m. After verification, the technician was able to re-establish normal control. The reservoir returned to its operating height at 7:30 a.m.

The event did not inconvenience waterway users and did not disrupt or cause any damage to the environment or residents. The water upstream of the dam was contained below the Moselle’s historical flood levels and inside the embankment.

The operator reported that a failure of the reservoir’s level measurement caused the event. The system featured a bulb-type probe, located in a manhole on the shoreline. The control system raised the valves following an incorrect low-level measurement. The emergency system, which uses different measurements, has made it possible to correct the situation. In addition, the operator notes that high grid voltage variations were not regulated by the inverter. This may have been related to the sensor’s failure.

The operator replaced the bulb-type level sensor and the inverter. A radar-type sensor was also installed in the reservoir’s level well to provide back up to the measurement instruments.