Numerical study of debris flows in presence of obstacles and retaining structures: A case study in the Italian Alps

Debris flows are one of the most frequent mass movement processes and occur in all regions with steep relief and at least occasional rainfall. Their high flow velocity, impact forces, and long runout, combined with poor temporal predictability, cause debris flows to be one of the most hazardous landslide types. An essential aspect of debris-flow risk management is the design of mitigation measures, which reduce the existing risk to an accepted level of residual risk, by reducing the potential damage that the moving mass can produce in terms of loss of human life and destruction of structures and infrastructures. Among these mitigation measures, transverse retention structures are used to delimit storage basins and prevent dangerous debris flows from reaching high-consequence areas. Due to the enormous impact forces that debris flows can exert on obstacles in their path, a reasonable planning requires that dynamic stresses are taken into account during the structural designing process, regardless of the complete (solid body barrier) or partial (open barrier) retention function that the type of selected structure can exert on the flowing mass. Since the village of Cancia, close to Cortina d’Ampezzo (Italian Dolomites), is hit by destructive debris flows for a long time, a storage basin delimited by natural and gabion barriers was built in 2000. In 2009 a severe event caused the partial collapse of the gabions and the overflow of the flowing mass. The present paper analyses through numerical modelling the dynamics of the flow and the influence of an abandoned building, existing inside the storage basin, on the occurred event.