Alessio Cislaghi

Regionalization of flow-duration curves through catchment classification with streamflow signatures and physiographic-climate indices

AbstractThis study addresses the estimation of flow-duration curves (FDC) in ungauged sites through the catchment classification. Forty-six catchments in the Upper Po river basin (Italy) were analyzed and classified through two different frameworks: the first scheme consists of the application of two clustering methods in a series considering six streamflow signatures, and the second one treats indexes of climate, physiography, soil, and land-use with the same clustering procedure. Catchments have been classified into three homogeneous groups: the first one is characterized by the lowest runoff and flash-flood events, the second one includes maximum runoff, and the third one shows intermediate behaviour. The estimation of FDCs was done using a lognormal distribution, whereas the regionalization was constructed applying a stepwise multiple linear regression, followed by a leave-one-out cross-validation. The results show great performance improvement when the regionalization model is found by taking account...

A Probabilistic 3-D Slope Stability Analysis for Forest Management

A 3-D physical-based approach to slope stability has been proven to be very promising in order to provide reliable spatially distributed landslides maps. Over large areas, however, such an approach still presents some limitations, mainly related to the variability and the uncertainty of the input parameters. By combining a 3-D physical-based model with a Monte Carlo technique, such constraints can be overcome, improving the performance and the applicability of the method. Whereas uncertainties of geotechnical, morphological and hydrological parameters have been widely investigated, few studies have been focused on the variability of root reinforcement, which plays a crucial role in preventing shallow landslides in forested areas. To contribute to define the effect of different forest management strategies on slope stability, we developed a 3-D model able to properly take into account for the effect of the root systems into the soil. The main objectives of our study are: (i) to define a probability distribution function for the root reinforcement according to the forest stands characteristics (tree density, mean diameter at breast height, minimum distance between trees), (ii) to obtain a probability distribution of the Factor of Safety through the combination between a 3-D slope stability model and a Monte Carlo simulation technique, and (iii) to evaluate the difference between several forest management scenarios in terms of shallow landslide risk. The model has been applied to a small Alpine area, mainly covered by coniferous forest and characterized by steep slopes and a high landslide hazard. Our findings contribute to provide forest managers with useful information for understanding the consequences of different forestry strategies.

Source areas, connectivity, and delivery rate of sediments in mountainous-forested hillslopes: A probabilistic approach

In mountainous-forested landscape, quantifying the materials produced at hillslope scale that effectively reach the channel network with a given probability is currently challenging, due to the uncertainties in modelling the frequency-magnitude distribution of failures and in determining the sediment connectivity between unstable areas and channel network. The purpose of this study is to develop a modular approach to assess the sediment source areas and the probability of mobilization from hillslope, and to estimate the probability of sediment input to the streams proposing a new connectivity index. The first goal was faced adopting a 3D probabilistic slope stability method that includes the spatially distributed characteristics of forest coverage. The second aim was tackled by comparing sediment travel distance and the minimum-topographic distance to reach the nearest stream. A simple deposition model was applied to estimate the percentage of the sediment entering into the stream network. The methodology was tested on three headwater catchments in northern Italian Alps. The outputs were landslide susceptibility maps, which showed robust performances when compared to the available landslide inventories (AUC > 0.726), and maps of the probability that sediment reaches the channel network. In this way, it was possible to identify which areas are the most susceptible to landsliding, how many sediment materials can be mobilised with a given probability, and which is the degree of sediment connectivity with the channel system. Results obtained for the tested catchments, compared with data available from the literature, showed that the proposed methodology is of general validity, especially for those territories characterized by rainfall-triggered landslides and forest coverage. This study, then, provides a robust framework to improve debris-flow risk management and to implement watershed management strategies, such as planning forestry operations or positioning retention structures addressed to increase slope stability and to reduce sediment delivery.