Catani, Filippo

Cinti, L.

Falorni, Giacomo

Leoni, Lorenzo

Segoni, Samuele

English

Florence Research

Geophysical Research Abstracts,Vol. 10, EGU2008-A-11056, 2008SRef-ID: 1607-7962/gra/EGU2008-A-11056EGU General Assembly 2008© Author(s) 2008Assessment of an infinite slope stability approach forshallow landslides: validation and sensitivity analysesL. Leoni, S. Segoni, L. Cinti, G. Falorni, F. CataniEarth Sciences Dept., University of Florence (lorenzo.leoni@unifi.it)In recent years several severe rainstorms have occurred in the Armea basin (Liguria,Italy). In at least two cases these have triggered numerous shallow landslides that havecaused victims and damaged roads, buildings and agricultural activities. These eventshave also led to several scientific studies and one of these has designated the area aspilot site for testing a methodology for forecasting the probability of occurrence ofshallow landslides. In its current stage the basic basin-scale model applied for predict-ing the probable location of shallow landslides involves several stand-alone compo-nents. A module for estimating soil saturation according to recorded precipitation, asoil depth prediction scheme and a limit-equilibrium infinite slope stability algorithmwhich produces a factor of safety (FS). Additional ancillary data (DEM, material co-hesion and angle of internal friction) are also required. The single components areseamlessly integrated into a system that publishes constantly updated FS values to aWebGIS in near-real-time so that local administrators responsible for public safety canaccess and download the data from the internet. This system has been running for sev-eral months and is now being validated and, where necessary, improved. Several typesof problems hinder a correct validation of the system. One major obstacle was over-come when a major storm triggered several tens of soil slips in the basin in December2006. This event provided both the necessary rainfall data for the soil saturation com-ponent, which until then was lacking, and a new landslide inventory for comparisonwith the FS produced by the slope stability model for the same event. The inventorywas derived from a newly acquired VHR satellite image. However, to precisely over-lay the image on the DEM used as topographic base for the limit-equilibrium infiniteslope stability model it is necessary to carry out an orthorectification of the image.This entails a time consuming procedure that in any case does not always lead to com-pletely satisfactory results: in the case of the Armea basin offsets were up to a few tensof meters, thereby sometimes decoupling the produced FS values from the landslideinventory by the same distance. For small events such as these this can make the dif-ference between accurately predicting an area of landslide occurrence and producingan error. Further uncertainty derives from how to consider a prediction as accurate.How many pixels within the landslide area should have a value near or below unity?Is one unstable pixel enough to destabilize a larger area? Where should the unstablepixels be located within the landslide scar? The work carried out to date attempts toanswer some of these questions. Although the study is still ongoing, initial results arequite good: most landslides generally occurred in the higher susceptibility areas andthe number of false positives is rather low. Another important aspect of the researchbeing performed regards the assessment of the relative importance of the different pa-rameters involved in the limit-equilibrium infinite slope stability model. This statisticalsensitivity analysis has the aim of determining which errors in the input variables slopegradient, soil depth, soil saturation, cohesion and angle of internal friction produce thelargest errors in the output FS values. Preliminary results indicate the importance oftopographic attributes and of soil depth.

Assessment of an infinite slope stability approach for shallow landslides: validation and sensitivity analyses

https://flore.unifi.it/bitstream/2158/384887/1/Leoni%20et%20al%20GRA%20vol%2010%20EGU%202008.pdf

Assessment of an infinite slope stability approach for shallow landslides: validation and sensitivity analyses

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