The canal bypasses the River Romanche. It is connected to a spillway channel of a hydroelectric plant and is located between the plant and the river. At the canal’s head is an isolation valve that is protected from debris by a screen. The channel’s water level is regulated by an automatic valve that releases water to the Romanche.
At around 4:00 p.m., a canal located downstream of a hydroelectric plant overflowed, causing flooding. An alarm alerted the operator that the level in the spillway channel was high. He arrived at the scene and saw the canal overflowing in the direction of homes and the channel overflowing in the direction of the River Romanche over a spillway wall. Seeing that the canal’s headgate was no longer operating automatically, he closed it by hand. The level in the channel immediately dropped below the overflow level. The cellars of six homes were flooded. The operator, accompanied by firefighters and gendarmes, met with the local residents to see the damage.
Equipment and organisational failures at cause
At the time of the event, the plant was operating in a degraded mode. The travelling screen, which cleans the trash rack at the canal head, had broken down due to the failure of its voltage limiter. The screen was therefore cleaned twice a day. This proved insufficient however, for the screen become clogged with grass clippings from along the channel’s banks. As a result, it was impossible to regulate the level in the channel because the opening of the channel valve leading to the river is controlled by the channel’s level.
In addition, the channel’s high-level alarm indeed went off as its water level rose. However, a failed fuse on its headgate prevented it being isolated before it overflowed.
