Risk management on an alluvial fan: a case study of the 2008 debris-flow event at Villar Pellice (Piedmont, N-W Italy)

Abstract. In the Piedmont Region (North-Western Italy), the regional authorities manage debris flow risk by following the ideal sequence of steps that are generally pursued in land planning and civil protection activities. Complex procedures and methods are elaborated and widely discussed with politicians, economists and the general public. On the contrary, in emergency situations, civil protection agencies generally prefer the adoption of simple and flexible criteria. In this paper, a catastrophic debris flow event, that occurred in 2008 in Villar Pellice, is described in this perspective, after an analysis of the triggering rainfalls and of the effects on human life and properties. The availability of a series of personal accounts coming from people who witnessed the occurrences before, during and after the event has allowed us to analyse, in detail, the dynamics of the event. Thanks to these accounts, it has been possible to propose new guidelines for the planning of the emergency activities in areas that are potentially prone to similar impulsive phenomena.

[1]  F. Luino.  Sequence of instability processes triggered by heavy rainfall in the northern Italy , 2005 .

[2]  J. D. Cheng,et al.  A Comprehensive Debris Flow Hazard Mitigation Program in Taiwan , 1997 .

[3]  F. Luino,et al.  The flood and landslide event of November 4–6 1994 in Piedmont Region (Northwestern Italy): Causes and related effects in Tanaro Valley , 1999 .

[4]  M. Rossi,et al.  The rainfall intensity–duration control of shallow landslides and debris flows: an update , 2008 .

[5]  O. Hungr,et al.  Debris flow defenses in British Columbia , 1987 .

[6]  Timothy R. H. Davies.  Using Hydroscience and Hydrotechnical Engineering to Reduce Debris Flow Hazards , 1997 .

[7]  José I. Barredo,et al.  Major flood disasters in Europe: 1950–2005 , 2007 .

[8]  Robert K. Mark,et al.  Operation of a real-time warning system for debris flows in the San Francisco bay area, California , 1993 .

[9]  Lorenzo Marchi,et al.  Alluvial Fans in the Italian Alps: Sedimentary Facies and Processes , 2009 .

[10]  T. K. Collins.  Debris flows caused by failure of fill slopes: early detection, warning, and loss prevention , 2008 .

[11]  J. N. Hutchinson,et al.  A review of the classification of landslides of the flow type , 2001 .

[12]  R. L. Keeney,et al.  Decisions with Multiple Objectives: Preferences and Value Trade-Offs , 1977, IEEE Transactions on Systems, Man, and Cybernetics.

[13]  Davide Tiranti,et al.  Quantitative basin characterisation to refine debris-flow triggering criteria and processes: an example from the Italian Western Alps , 2008 .

[14]  Dieter Rickenmann,et al.  Empirical Relationships for Debris Flows , 1999 .

[15]  Ralph L. Keeney,et al.  Decisions with multiple objectives: preferences and value tradeoffs , 1976 .