Articles | Volume 15, issue 5
Research article
21 May 2015
Research article |  | 21 May 2015

Site-specific to local-scale shallow landslides triggering zones assessment using TRIGRS

M. Bordoni, C. Meisina, R. Valentino, M. Bittelli, and S. Chersich

Abstract. Rainfall-induced shallow landslides are common phenomena in many parts of the world, affecting cultivation and infrastructure and sometimes causing human losses. Assessing the triggering zones of shallow landslides is fundamental for land planning at different scales. This work defines a reliable methodology to extend a slope stability analysis from the site-specific to local scale by using a well-established physically based model (TRIGRS-unsaturated). The model is initially applied to a sample slope and then to the surrounding 13.4 km2 area in Oltrepò Pavese (northern Italy). To obtain more reliable input data for the model, long-term hydro-meteorological monitoring has been carried out at the sample slope, which has been assumed to be representative of the study area. Field measurements identified the triggering mechanism of shallow failures and were used to verify the reliability of the model to obtain pore water pressure trends consistent with those measured during the monitoring activity. In this way, more reliable trends have been modelled for past landslide events, such as the April 2009 event that was assumed as a benchmark. The assessment of shallow landslide triggering zones obtained using TRIGRS-unsaturated for the benchmark event appears good for both the monitored slope and the whole study area, with better results when a pedological instead of geological zoning is considered at the regional scale. The sensitivity analyses of the influence of the soil input data show that the mean values of the soil properties give the best results in terms of the ratio between the true positive and false positive rates. The scheme followed in this work allows us to obtain better results in the assessment of shallow landslide triggering areas in terms of the reduction in the overestimation of unstable zones with respect to other distributed models applied in the past.

Short summary
This manuscript defines a reliable methodology for shallow landslides triggering zones assessment at site-specific or local scales by using a well-established physically based model (TRIGRS-unsaturated) based on the calibration of the model at slope scale using soil hydrological behavior analyzed through a continuous field monitoring. Moreover, the paper analyzes the effects on triggering zones assessment of taking into account for different unit mapping of the slope soils of a studied area.
Final-revised paper