Refurbishment and Installation of a Monitoring and Early Warning System on the Sierroz Embankments in Aix-les-Bains, France

Abstract

Sierroz embankments are located in an urban area, in the city of Aix-les-Bains (Savoie, France). Their linear is 400m on both rims. These embankments protect about 900 people against Sierroz river floods. Hydraulic studies performed in the frame of the Aix-les-Bains Inundation Risk Prevention Plan (PPRI in French) have shown that these embankments have a high risk of failure by overtopping during a 100 year return period flood of the Sierroz River. These studies have defined inundation maps with High Danger areas. From these results, the city of Aix-les- Bains asked EDF to perform a safety assessment study, in order to assess the safety margins of these embankments for each of their potential failure modes: overtopping erosion, internal erosion, slope sliding and liquefaction. This study confirmed that the main risk is breaching by overtopping erosion during flood. This diagnosis led the city of Aix-les-Bains to launch two parades: (i) the embankment refurbishment in order to provide them satisfactory safety margins during a 100 year return period flood and (ii) a monitoring and early-warning system able to alert population at risk as early as possible when breaching is imminent. These two parades are presented including environmental constraints and cost estimates.