Abstract
Autogenic processes, such as sudden avulsions, unexpected channel migrations and backfilling phenomena, can considerably alter the propagation of sediment-laden flows on alluvial fans. Once the initial and boundary conditions of the hazard scenario with a given return period are determined, the delineation of the associated exposed areas is based on one numerical, essentially deterministic, process simulation, which may not adequately reflect the underlying process variability. By following a ‘similarity-of-process concept’ we generated sediment-laden flows on an experimental alluvial fan. Thereby, we considered an alluvial fan model layout with a curved guiding channel and featuring a convex shape. As loading conditions, we defined a reference, an increased and a reduced level for the released water volume and the predisposed solid fraction. Further, we imposed two different stream power regimes and executed, for each factor combination, eight experimental runs. The associated exposure areas were recorded by video and were mapped in a GIS. We then analyzed exposure data and derived exposure probability maps superposing the footprints of the eight repetitions generated by each experimental loading condition. The patterns of exposure associated with specific loading conditions showed a noticeable variability due to the main effect of the total event volume, the solid fraction and the interactions between them and with the imposed stream power in the feeding channel. Our research highlights that a probabilistic notion of exposure in risk assessment and mitigation needs to be considered. Further, a major challenge consists in adapting numerical codes to better mirror the stochastics of process propagation for more reliable flood hazard and risk assessments.
Dynamic Risk Assessment of Ultra-Shallow-Buried and Large-Span Double-Arch Tunnel Construction
