Debris flow modelling in Julian Alps using FLO-2D

Abstract

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 geological-geomorphological 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.