Controls on modern alluvial fan processes in the Central Alps, Northern Italy

Alluvial fan development in Alpine areas is often affected by catastrophic sedimentary processes associated with extreme floods events, causing serious risks for people living on the fans. Hazard assessment in these areas depends on proper identification of the dominant sedimentary processes on the fans. Data from a set of 209 alluvial fans from the central Alps of Italy are presented in this paper and analysed with the help of various statistical techniques (linear regression, principal components analysis, cluster analysis, discriminant analysis and logistic regression). First, we used modern sedimentary facies and historical records (flood events since 15th century), to distinguish between the two dominant sedimentary processes on alluvial fans: debris flows and streamflows. Then, in order to analyse the main controls on past and present fan processes, 36 morphological, geological and land-use variables were analysed. As with observations for arid-environment fans, catchment morphology is the most influential factor in the study area, whereas geology and land use are minor controls. The role of climatic change and landsliding within the catchments also seems to be very important and is discussed. Statistical techniques also help in differentiating groups of alluvial fans by sets of controlling factors, including stage and type of evolution. Finally, by using discriminant analysis and logistic regression, we classified alluvial fans according to the dominant sedimentary process, with a success rate ranging between 75 and 92 per cent.