Abstract
In this work, we present a novel quantitative geographical information system-based procedure to obtain the magnitude (area) and frequency of medium to large first-time shallow slope failures. The procedure has been set up at the Barcedana Valley, in the Tremp Basin (Eastern Pyrenees). First, pixel-based susceptibility classes were defined using a slope stability index obtained with the physically based model SINMAP. The frequency calculated from the number of first-time failures recorded during the last 60 years was then assigned to each susceptibility class. We devised a procedure to estimate the size of potential failures by means of the aggregation of pixels within the boundaries of morphological slope units, optimized for the purpose. Finally, the landslide hazard was prepared using the magnitude-frequency matrix. Results show that a proper pixel clustering has been carried which avoids the generation of small groups of pixels with different susceptibility degrees within the same slope unit. For a given hill slope, the area of the cluster of pixels depends on the size of the slope unit, which is not unique as it depends on the criterion used to delineate them. Therefore, the latter is a key factor in the final results. In this study, we validated our results with the size distribution of the observed landslides. The methodology presented in this work can be applied using any susceptibility assessment method with a pixel-based output.
Highlights
Magnitude and frequency are the two key factors for a quantitative assessment of landslide hazard (Dai et al 2002; Fell et al 2005; Picarelli et al 2005; Van Den Eeckhaut et al 2007; Corominas et al 2014; Lari et al 2014; Vranken et al 2014)
The concept of intact slopes is not straightforward as strictly speaking, they do not exist in nature: evidences of slope processes acting in the past are not present after a few years due to the erosive cycle
Other input parameters are required for using the software; their role in the SU delineation is more technical and it is described in detail in Alvioli et al (2016); we focus here only on the determination of suitable c and a parameter values, which are directly related to the local terrain morphology
Summary
Magnitude and frequency are the two key factors for a quantitative assessment of landslide hazard (Dai et al 2002; Fell et al 2005; Picarelli et al 2005; Van Den Eeckhaut et al 2007; Corominas et al 2014; Lari et al 2014; Vranken et al 2014). Based models require higher resolution data, with respect to statistical ones, typically geotechnical parameters of the soil Such data is often difficult to obtain on large areas, and for this reason, probabilistic approaches have been introduced, for example using TRIGRS in Raia et al (2014) and Salciarini et al (2017). Another limitation posed by the physically based models accounting for water infiltration is the dependence on the initial water table depth (Baum et al 2005), which is difficult to estimate and needs to be measured on the field. An evaluation of the different options for data gathering for physically based models, for TRIGRS, was recently described in Yatheendradas et al (2019)
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