Field Surveys and Numerical Modeling of Pumiceous Debris Flows in Amalfi Coast (Italy)

Abstract

The first objective of the work is to test a cost-effective tool for the collection of debris flows (DF) field data such as volumes, peak flow depths and deposit depths. Secondly, we show how these data can be used for the calibration of a depth-averaged propagation model. The case study is a DF of pumiceous sediments, occurred in the Amalfi Coast (Southern Italy) in October 2013. The DF path is a steep channel, ending in a small debris fan delimitated by a gabion wall. The risk is high because DFs, having a return period of just few years, overtop the wall and hit a busy road. Both terrestrial laser scanner (TLS) and photogrammetric techniques were employed to survey the topography, before and after the event under study. The images of the channel were taken from an unmanned aerial vehicle (UAV). Digital terrain models (DTM) were obtained pre and post event while the traces left by the DF along the channel banks allowed the estimation of the peak flow depths.A finite volume two-dimensional numerical code (FLATModel), based on shallow-water equations, was used for modelling the propagation and deposition of the DF under study. Both Voellmy and pure Coulomb friction resistance laws were tested. The numerically predicted deposit was compared to the post event DTM. Such comparisons showed a good agreement in terms of both depths and shape of deposit. The calibrated model could be used to predict the DFs run-out distances in similar contexts.