Large scale debris-flow hazard assessment: a geotechnical approach and GIS modelling (original) (raw)
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E3S Web of Conferences
The Alpi Apuane (Italy) are located a few kilometres from the coast of the Ligurian Sea, and they are characterized by peak elevations up to two thousand meters above sea level, as well as narrow, deeply incised valleys and steep slopes. Due to these morphoclimatic conditions, heavy rains are frequent, causing floods, landslides, and debris flows, particularly within the Vezza catchment. In this work we applied two different hydrological-hydraulic models to this catchment, focusing on the catastrophic debris flow event of June 19, 1996. Firstly, recent, well-documented rainfall events were used to validate the engineering geological model of the study area, then we began to analyse the rainfall-runoff and debris flow event of 1996 in the Cardoso sub-catchment. As models, we used the FLO-2D and a novel experimental model, developed by some of the authors and based on TRENT2D, in which the dynamic of a debris flow is fully coupled with the rainfall-runoff response of a basin. Prelimin...
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The Serchio River Valley, in north-western Tuscany, is a well-known tourism area between the Apuan Alps and the Apennines. This area is frequently hit by heavy rainfall, which often triggers shallow landslides, debris flows and debris torrents, sometimes causing damage and death. The assessment of the rainfall thresholds for the initiation of shallow landslides is very important in order to improve forecasting and to arrange efficient alarm systems.
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In recent decades, the Entella River basin (eastern Liguria) has been affected by several rainfall events that induced widespread shallow landslides and earth flows on the slopes; roads, buildings, structures and infrastructure suffered extensive damage due to the instability processes. In this paper, a GIS-based approach for analyzing and assessing a simplified landslide susceptibility in the Entella River catchment is presented. Starting from landslide information mainly provided from newspaper articles and unpublished reports from municipal archives, we performed a series of comparative analyses using a set of thematic maps to assess the influence of predisposing natural and anthropic factors. By evaluating the statistical distribution of landslides in different categories, we assigned weighted values to each parameter, according to their influence on the instability processes. A simplified, reproducible, but effective approach to assess landslide susceptibility in the study area...
Application of a process-based shallow landslide hazard model over a broad area in Central Italy
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Process-based models are widely used for rainfallinduced shallow landslide forecasting. Previous studies have successfully applied the U.S. Geological Survey's Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS) model (Baum et al. 2002) to compute infiltration-driven changes in the hillslopes' factor of safety on small scales (i.e., tens of square kilometers). Soil data input for such models are difficult to obtain across larger regions. This work describes a novel methodology for the application of TRIGRS over broad areas with relatively uniform hydrogeological properties. The study area is a 550-km 2 region in Central Italy covered by post-orogenic Quaternary sediments. Due to the lack of field data, we assigned mechanical and hydrological property values through a statistical analysis based on literature review of soils matching the local lithologies. We calibrated the model using rainfall data from 25 historical rainfall events that triggered landslides. We compared the variation of pressure head and factor of safety with the landslide occurrence to identify the best fitting input conditions. Using calibrated inputs and a soil depth model, we ran TRIGRS for the study area. Receiver operating characteristic (ROC) analysis, comparing the model's output with a shallow landslide inventory, shows that TRIGRS effectively simulated the instability conditions in the post-orogenic complex during historical rainfall scenarios. The implication of this work is that rainfall-induced landslides over large regions may be predicted by a deterministic model, even where data on geotechnical and hydraulic properties as well as temporal changes in topography or subsurface conditions are not available.
2015
Hydrogeological hazards are widespread and recurrent in Italy, requiring constant monitoring, prevention and mitigation activities. This paper contributes to the landslide forecast debate, analysing the relationship between rainfall and landslides in the eastward section of the Esino river basin located in the Marche region (central Italy). This area of similar hydrogeological properties is characterized by post-orogenic quaternary sediments prone to rainfall-induced shallow landslides. The preliminary investigation revealed the occurrence of 232 landslides, most of all shallow and small-sized, from 1953 to 2011. Rainfall data from neighbouring rain gauges were compared with the historical series of landslides both on annual and monthly basis. Moreover, the intensity-duration empirical model is applied to describe a new empirical triggering threshold valid for the study area. Threshold rainfall conditions are described by the equation: I ¼ 1:61 Â D À0:21 where I = mean rainfall intensity (mm/h) and D = rainfall duration (h). Such equation represents the conditions that in the past decades activated 90 % of all landslides occurred within the area. This rainfall threshold could be used to forecast landslides occurrence in the post-orogenic complex of the Esino river basin.
1 The Functional Centre (CFMR) of the Civil Protection of the Lombardy Region, North Italy, 2 has the main task of monitoring and alerting, particularly with respect to natural hazards. The 3 procedure of early warning for hydrogeological hazard is based on a comparison of two 4 quantities: thresholds and rainfall, both referred to a defined area and an exact time interval. 5 The CFMR studied 52 landslide events (1987-2003) in Medium-Low Valtellina and derived a 6 model of the critical detachment rainfall, in function of the local slope and the Curve Number 7 CN (an empirical parameter related with the land cover and the hydrological conditions of the 8 soil): it's physically consistent and allows a geographically targeted alerting. Moreover, 9 rainfall thresholds were associated with a typical probability of exceedance. 10
Regional hydrological thresholds for landslides and floods in the Tiber River Basin (central Italy)
Environmental Earth Sciences, 1998
The definition of landslide warning thresholds, based on the analysis of hydrological data, is proposed. In the Tiber River Basin of central Italy historical information on landslides and floods, for the period 1918–1990, was available from a nationwide bibliographical and archive inventory on geohydrological catastrophes. Hydrological data were obtained from mean daily discharge records at various gauging stations within the basin. Several hundred hydrological events, broadly defined as a series of consecutive days having mean daily discharge exceeding a predefined value, were identified. Hydrological parameters obtained from the discharge records were used to rank the events according to their probability to trigger mass movements or inundations and to define regional thresholds for the occurrence of landslides and floods. The proposed approach, not lacking limitations, has conceptual and operational advantages, among which is the possibility of using historical information on geohydrological catastrophes.
Canadian Geotechnical Journal
The assessment of rainfall-induced shallow landslide hazards at the catchment scale poses a significant challenge. Traditional empirical approaches for landslide hazard assessment often assume that conditions having caused failure in the past will not change in the future. This assumption may not hold in a climate change scenario. Physically based models (PBMs) therefore represent the natural approach to include changing climate effects. PBMs would in principle require the combination of a three-dimensional (3-D) mechanical and water-flow model. However, a full 3-D finite element model at the catchment scale, with relatively small elements required to capture the pore-water pressure gradients, would have a significant computational cost. For this reason, simplifications to the mechanical (i.e., infinite slope) and water-flow models (i.e., one-dimensional or hybrid 3-D) are introduced, often based on a priori assumptions and not corroborated by experimental evidence. The paper presen...