Diversity of Rainfall Thresholds for early warning of hydro-geological disasters

Abstract. For early warning of disasters induced by precipitation (such as floods and landslides), different kinds of rainfall thresholds are adopted, which vary from each other, on the basis on adopted hypotheses. In some cases, they represent the occurrence probability of an event (landslide or flood), in other cases the exceedance probability of a critical value for an assigned indicator I (a function of rainfall heights), and in further cases they only indicate the exceeding of a prefixed percentage a critical value for I, indicated as Icr. For each scheme, it is usual to define three different criticality levels (ordinary, moderate and severe), which are associated to warning levels, according to emergency plans. This work briefly discusses different schemes of rainfall thresholds, focusing attention on landslide prediction, with some applications to a real case study in Calabria region (southern Italy)

Analysis of Flood Series by Stochastic Models

"Flood analysis for regions, like Southern Italy, where the annual flood series exhibits outliers (and, then, high skewness), associated with disastrous storms, requires building suitable stochastic models. In such cases, the usual simple model (Model A), which assumes the largest annual flood to be the maximum of a Poissonian number of indepen dent random variables with common exponential distribution function, proves to be inadequate. Better models can be built by replacing the hy_ potheses on which Model A is based with others, phenomenologically closer to reality, namely, that the number of exceedances in a year is still a non-homogeneous Poisson process, but the exceedance values are not identically distributed random variables. Of the two models considered, i.e., a time-dependent distribution for the exceedancemagnitude (Model B) and a mixed exponential distribution (Model C), the latter is found to give a better statistical fit. There is also better phenomen-ological support for Model C in that disastrous storms occur more rarely but with much larger intensities than others, and they are accordingly better modelled as belonging to different populations.

An Instrumented Flume for Infiltration Process Modeling, Landslide Triggering and Propagation

Rainfall is the most common cause of landslides, so it is important to know the processes underlying failure starting with the rainfall infiltration processes into the granular soils, the distribution of the water content and pore pressure in both saturated and unsaturated layers, to include their effects in terms of slope stability. Although the literature is full of simulation models, the complexity of phenomena would impose a more detailed analysis by a well-equipped flume. For that purpose, a meter-scale laboratory experiment at the University of Calabria was designed and built. It is very useful for carrying out complex tests to analyze the response of loose soils or debris in terms of stability. It is composed of two channels: the first one was adopted for analyzing the triggering mechanisms, the second one for the propagation phases. Both channels are equipped with suitable sensors for monitoring the main physical variables, i.e., spray nozzle systems to apply a specific rainfall intensity; minitensiometers and TDR (Time Domain Reflectometry) for measuring, respectively, suction values and water content; miniaturized pressure transducers for pore water pressures; and laser displacement sensors. This paper describes in detail the instrumented flume and explores its potential through the analysis of a homogeneous slope of pyroclastic soil. An experiment was carried out to reproduce landslide triggering in pyroclastic soils, evolving in mudflow, by considering a homogeneous deposit. The measurements carried out allowed testing the apparatus, describing the behavior of the soil after rainfall infiltration and better identifying factors particularly significant in the collapse mechanism and process evolution

Regional flood frequency estimation using the two-component extreme value distribution.

"The two-component extreme value (TCEV) distribution, suggested for modelling Italian annual flood series (AFS), is shown to account both for the presence of flow outliers and for the high variability of the skewness of historical AFSs. Using such a model, it is found that the T-year flood varies with log(T) much more rapidly for large values of T than is the case for small values of T. The presence of four parameters in the TCEV distribution introduces great uncertainty in estimating the T-year flood when the parameters are estimated from a single series. Regional analysis, which exploits basin similarities, is then needed, not only at ungauged sites but also at gauged ones. Regionalization techniques, by which all flood data over a region are combined to produce a single regional flood distribution, are described and their application to Italian data is shown.

Integrated Physically based System for Modeling Landslide Susceptibility

AbstractRainfall induced shallow landslides cause significant damages involving loss of life and properties. Predict susceptible locations for rainfall induced shallow landslides is a complex task that involves many disciplines: hydrology, geotechnical science, geomorphology, statistic. Usually to accomplish this task two main approaches are used: statistics or physically based model. In this paper an integrated system for early warning of rainfall induced shallow landslides is presented. It is based on a hydrological model for solving 3D-Richards equation, a component for safety factor maps computation under infinite slope hypothesis and a GIS for model outputs visualization. The system is tested in Calabria (South Italy) for two river basins in which landslides occurred in the period from 8 to 10 March 2010. Results in terms of time evolution and spatial maps of safety factor at various depths are presented and compared to landslides maps

Study of an active landslide on A16 Highway (Italy): modeling, monitoring and triggering alarm

This paper presents the preliminary results of a study carried out on an active landslide, which insists on the A16 (E842) Highway, between Campania and Puglia region (South of Italy). The area lies at the foot of a large gravitational mass, classified as “ancient landslide deposit” where a system of landslides, with different types and activity states, are present. It is characterized by the widespread presence of clayey sequences that affect the stability of the slopes looming over the highway. The site has been instrumented with a series of automated sensors, both innovative and traditional, which monitor different physical entities. Furthermore, a photogrammetry survey was carried out with a drone in order to know precisely the geometry of the slope. Once the geotechnical and hydraulic parameters were collected, a 2D finite difference numerical model (FLAC® software) of the slope was set up and a series of back analysis were carried out comparing the model results with those obtained from the monitoring database. Through these back analyses, the choice of the geotechnical parameter was refined and validated. Different physical variables and results are shown into a unique representation, in comparison with the developed model and the geological and geotechnical information. Following the trends of data, the weekly/monthly average displacements and the possible causes (heavy rainfall, raising of the water table), it is possible to study the mechanical behavior of the landslide and establish preliminary warning thresholds, which have to be verified in future. The large number of acquisitions, provided by the automated monitoring system, permits to use a statistical approach in order to identify a good reliability and increase the confidence on the results. The obtained knowledge allows for the automation of the data processing procedure and for the control of the highway stability in near real time

Caratterizzazione di un tronco fluviale del fiume crati e sperimentazione con modellazione idraulica monondimensionale

Obiettivo della ricerca è l’acquisizione delle informazioni idrologiche ed idrauliche deducibili dall'analisi di idrogrammi di livelli sincroni misurati in due diverse sezioni del fiume Crati mediante l'utilizzo di un modello idraulico di propagazione