Prévision par modélisation numérique de la zone de risque bordant un tronçon de rivière subissant une crue exceptionnelle

The direct impacts of floods are often considered as limited to the maximum downstream area exposed to the flooding. Considering the size of exceptional floods, the river bed could undergo deep changes. Pairing the GSTARS sediment transport model to a slope stability model (modified Bishop method) that we developed, this paper presents a methodology leading to the definition of a true safety zone along the shores as it takes into account the risk of floods and soil movements: each section of this river undergoes changes due to sediment-fluvial hydraulics ( erosion-deposit) and then eventual landslides modify the profiles. To analyze this, we had first to determine the hydraulic and geotechnical characteristics then use them to test the slope stability of the various legs of the watercourse before and during flooding. The application of this method to a tributary of the Saguenay River for the 1996 "downpour" shows a very good correlation of results with those collected in situ. The method can be directly a...