ABSTRACT
Analysis of different scenarios is addressed for the Mallero river, a mountain stream in northern Italy. A town (Sondrio) is present at the downstream end of the river. Flood hazard for Sondrio can be related either to flood events with significant sediment transport (because the in-town reach is a preferential location for aggradation processes with resulting increase of the water elevation) or to dambreak events (in case of collapse of a major landslide at relatively short distance upstream). Therefore, the manuscript explores the use of hydro-morphologic modelling to assess the level of hazard related with the scenarios for flood with intense sediment transport and for landslide and following dam-break wave. For the first scenario, a past event (flood of 1987) is considered, that has been already object of previous investigations. Propagation of the flood wave and resulting river morphologic changes are modelled using the coupled Saint-Venant and Exner equations. For the second scenario, different models are combined in an integrated process chain: available estimations of the landslide volume and models for dam breaching are used to create inflow conditions in terms of water and sediment discharge into the river, then the wave propagation is modelled again using the shallow-water, one-dimensional approach. For both scenarios, the analysis is devoted to assessing if these waves could be able to transport a significant amount of sediments to Sondrio, maximum elevation of the water surface and characterization of the time scales for the events. The role of analyses such as that presented here for territorial management and protection is discussed.
