77 L A N D F O R M E V O L U T I O N I N M O U N T A I N A R E A S STUDIA GEOMORPHOLOGICA CARPATHO-BALCANICA Vol. XLIV, 2010: 77–112 PL ISSSN 0081-6434 MARCELLA BIDDOCCU 1 , LAURA TURCONI 1 , DOMENICO TROPEANO 1 , SUNIL KUMAR DE 2 (TORINO) SLOPE INSTABILITY AND FLOOD EVENTS IN THE SANGONE VALLEY, NORTHWEST ITALIAN ALPS Abstract. Slope instability and streamflow processes in the mountainous part of the Sangone river basin have been investigated in conjunction with their influence on relief remodelling. Through histor- ical records, the most critical sites during extreme rainfalls have been evidenced, concerned natural parameters and their effects (impact on man-made structures) reiterated over space and time. The key issue of the work is the simulation of a volume of detrital materials, which might be set in motion by a debris flow. Two modelling approaches have been tested and obtained results have been evaluated using Debris© (GEOSOFT s.a.s.) software. Simulation of debris flow in a small sub-catchment (Tauneri stream) was carried out and the thickness of sediment “package” that could be removed was calculated in order to assess the debris flow hazard. The Turconi & Tropeano formula (2000) was applied to all the partitions of the Sangone basin in order to predict the whole sediment volume which might be delivered to the main stream during an extreme event and the result being 117 m 3 /hectare. Key words: landslip, torrential flood, debris flow, predictive model INTRODUCTION The Alpine valleys, throughout centuries, are in search of an equilibrium between anthropogenic activity and natural processes; interventions due to ameliorating productivity, accommodation and safety conditions for Man and environment often were done overlapping or contrasting the slowly-operating exogenous agents. Sometimes the man-made structures resulted to increased damaging effects of natural events, such as slope failure and torrential flooding. The Sangone valley is situated along the western border of the Torino plain and possesses patches of intensely built-up areas. The valley has frequently been affected by flood hazard, even today (November 1994; October 2000). The Sangone river and its tributaries as well as shallow slides brought damage to roads and threatened several housings. This paper examines processes of geomorphological instability characteris- ing the upper Sangone valley. Attention is focused on some aspects conditioning