Abstract.To set an approach for the future territorial planning, the Geological Survey of Friuli Venezia Giulia Region, through the researchers of Trieste University, started a program of debris-flow risk analysis using Flo-2D software as tool to delimit the hazardous areas. In the present paper, as a case study, a debris flow, called Fella sx, occurring in a torrent catchment was analyzed. The choice was due to the abundance of information about past events, inundated areas, rain fall, geology and to its representativeness. An initial back-analysis investigation identified a couple of representative rheological parameters. Riverbed samples were collected, sieve analyses were performed and rheological tests were carried out on the fraction finer than 0.063 mm using a rotationally controlled stress rehometer equipped with the serrated parallel plate geometry. The shear dependent behaviour was examined at different concentrations ranging from 33 to 48%, by weight. Viscosity data treatment was performed to determine the most suitable rheological model to provide the best approximation of the debris-flow behaviour. The rheological parameters, derived from experimental data, were used and compared with those obtained through the back-analysis and with the real inundated area. Data obtained through rheological analysis are useful in constructing scenarios of future events where no data for back-analysis are available.

Val Canale Valley is located in the Italian Julian Alps, in the north-eastern corner of Friuli Venezia Giulia Region. On 29 August 2003, the area has been invested by a strong intensity meteorological event (rainfall maxima from Pontebba station, which recorded the highest rainfall depths, were characterised by return periods in the range of 500-1000 years for 3-h, 6-h and 12-h periods) that caused debris flow phenomena. These have damaged infrastructures and killed people. In collaboration with the Geological Service of Friuli Venezia Giulia Region and with the contribution, for the input data, of the Department of Territory and Sour-Forest Systems of the University of Padova, we investigated twelve river basins located in the studied valley with different geologicalgeomorphological characteristics. The main objective of the study is to model the debris flow phenomena. This goal has been obtained using FLO-2D software. In all the basins implicated, we have collected samples for grain size curve distributions and rheological analyses in order to characterize the detritical material. First of all it has been necessary to execute a back analysis study with the aim of better define all the parameters involved. Subsequently, the goal has been to simulate a new alluvional event with a return time of 200 years, on the basis of actual morphology obtained from laser scan data (where data have been available) realizing a DEM based on a grid cell size of 5 m. On this topographic base it has been possible to insert the defence infrastructures realized after the alluvional event. From all this input data it has been possible to model and to simulate the potential debris flow with the aim to obtain, vulnerability first, and hazard mapping later, necessary for the future territorial planning.