Check Dam Behavior Under Extreme Circumstances at Villeneuve (Switzerland)

Abstract

The Tinière torrent is located in the western part of Switzerland and has its exutory in the Lake of Geneva. In 2006 and 2007, major flood events generated deposition of 10,000 m³ of solid material along the canalized part and more than 100,000 m³ in the upstream ravines. These deposits have caused the inundation of urbanized areas as well as erosion of torrent banks upstream. Also, several bridges have been destroyed. Detailed hazard mapping has shown significant risk of damage to the federal highway A9 as well as to the main railway and cantonal highway crossing Villeneuve for flood events between 100 and 300 years. Hence, three check dams have been constructed in the upstream part of the torrent. The retention volumes created by these dams aim at retaining the major part of the solid material that is being transferred during major flood events. However, during construction of the check dams, in July 2013, a major flood event has occurred at the construction site. A series of debris flows filled up the volume behind the most upstream located dam (~5,000 m³). This structure was not yet finished at the time of the event, only the concrete core of the dam was put into place. The event has caused damage to the structure but has saved Villeneuve from potential damage. In the following, the 2013 flood event and its crisis management are presented, together with the behavior of the partially constructed check dam and its positive impact on downstream safety.