shallow landslides susceptibility assessment in different environments

The spatial distribution of shallow landslides is strongly influenced by different climatic conditions and environmental settings. This makes difficult the implementation of an exhaustive monitoring technique for correctly assessing the landslide susceptibility in different environmental contexts. In this work, a unique methodological strategy, based on the statistical implementation of the generalized additive model (GAM), was performed. This method was used to investigate the shallow landslide predisposition of four sites with different geological, geomorphological and land-use characteristics: the Rio Frate and the Versa catchments (Southern Lombardy) and the Vernazza and the Pogliaschina catchments (Eastern Liguria). A good predictive overall accuracy was evaluated computing by the area under the ROC curve (AUROC), with values ranging from 0.76 to 0.82 and estimating the mean accuracy of the model (0.70–0.75). The method showed a high flexibility, which led to a good identification of the most significant predisposing factors for shallow landslide occurrence in the different investigated areas. In particular, detailed susceptibility maps were obtained, allowing to identify the shallow landslide prone areas. This methodology combined with the use of the rainfall thresholds for triggering shallow landslides may provide an innovative tool useful for the improvement of spatial planning and early warning systems

The role of land use changes in the distribution of shallow landslides

The role of land use dynamics on shallow landslide susceptibility remains an unresolved problem. Thus, this work aims to assess the influence of land use changes on shallow landslide susceptibility. Three shallow landslide-prone areas that are representative of peculiar land use settings in the Oltrepò Pavese (North Apennines) are analysed: the Rio Frate, Versa and Alta Val Tidone catchments. These areas were affected by widespread land abandonment and modifications in agricultural practices from 1954 to 2012 and relevant shallow landslide phenomena in 2009, 2013 and 2014. A multi-temporal land use change analysis allows us to evaluate the degree of transformation in the three investigated areas and the influence of these changes on the susceptibility to shallow landslides. The results show that the three catchments were characterised by pronounced land abandonment and important changes in agricultural practices. In particular, abandoned cultivated lands that gradually recovered through natural grasses, shrubs and woods were identified as the land use change classes that were most prone to shallow landslides. Additionally, the negative qualities of the agricultural maintenance practices increased the surface water runoff and consequently intensified erosion processes and instability phenomena. Although the land use was identified as the most important predisposing factor in all the study areas, some cases existed in which the predisposition of certain areas to shallow landslides was influenced by the combined effect of land use changes and the geological conditions, as highlighted by the high susceptibility of slopes that are characterised by adverse local geological (thick soils derived from clayey-marly bedrocks) and geomorphological (slope angle higher than 25°) conditions

Differences between mechanical and electrical cone penetration test in the liquefaction hazard assessment and soil profile reconstruction

Liquefaction - hazard assessment is often accomplished by means of simplified procedures, which are based on CPT. The CPT liquefaction procedures, generally, require cone penetration test with electrical tip or the measure of u (CPTu); however, in most countries, as Italy, penetrometric tests are carried out with mechanical tip (CPTm). Generally, CPTm leads to an estimate of the Liquefaction Potential lower than that inferred from CPTu. Moreover, CPTm has a reduced resolution in soil profiling. While the cone – shape effects on qc are not very relevant, those on fs can strongly influence the FSL calculation, especially in the case of silty sands. Within this framework, the main aim of this work is to identify the differences in liquefaction - hazard evaluation and soil profile interpretation in pairs of CPTm/CPTu. After that, two methodologies were used to correct CPTm results. At first, it was developed an empirical correlation between the sleeve friction measured with CPTm and that measured with electrical CPT/CPTu. After that, a method developed in literature was applied to the same CPTm/CPTu pairs. The two corrections were compared in order to see which one led to the best results in terms of enhancement of the liquefaction hazard assessment and soil profile reconstruction. Tests have been carried out in the area interested by the 2012 Emilia earthquake (Italy)

Evaluation of anthropogenic effects on the sediment delivery dynamics in response to slope instability

In this work a sediment connectivity assessment was performed in order to evaluate the role of anthropogenic effects on the sediment delivery dynamic, in response to slope instability. In particular, the potential connection of sediment source areas with the main channel networks and roads was investigated. Two catchments with different size and morphological setting were analysed: the Rio Frate and Versa catchments (Oltrepo Pavese, Northern Apennines, Italy). The two areas were affected by important anthropogenic effects, such as land use changes, drainage system and road network modifications. Moreover, several shallow landslides occurred in these areas in 2009 and 2013. The performed analysis allowed to obtain maps of sediment connectivity according to the main landscape modification due to human activities. In particular, the effects of these modifications on the degree of connectivity between shallow landslides, roads and streams, were investigated. In addition, the instability phenomena characterised by the highest connectivity were determined, allowing the determination of the areas where the mobilized sediment from shallow landslides can potentially reach roads and stream network, causing potentially extensive damages

The role of human activities on sediment connectivity of shallow landslides

Sediment connectivity within a catchment depends largely on the morphological complexity of the catchment and is strictly related to the anthropogenic modification of the landscape. In this context, the present research evaluates the role of anthropogenic effects on landscape modifications and the resulting influence on sediment delivery. An assessment of sediment connectivity was carried out for three different human impact scenarios: (i) drainage system density reduction, (ii) road network variation and (iii) land use changes. In addition, shallow landslides were used as sediment source areas to evaluate the potential connection between these sediment sources and downstream areas (e.g. main channels and road network). Two small catchments in the Oltrepò Pavese area (Northern Apennines, Italy), with different size and morphological setting, were analysed: the Rio Frate (1.9 km2) and the Versa (38 km2) catchments. In both areas, several shallow landslides were triggered in 2009 (Rio Frate and Versa) and in 2013 (Versa). Results highlight the role of the landscape complexity in coupling/decoupling upstream sediment sources, such as shallow landslides, from the main channel network and roads. In addition, the analysis identified instability phenomena characterized by high connectivity values, allowing determination of the areas in which mobilized sediment could potentially damage important infrastructures such as the road network or contribute to flooding induced by aggradation or obstruction of the river bed. The proposed approach provides a methodological framework to help improve watershed and land management strategies, especially in shallow landslides prone-areas

Integrating remote sensing and GIS techniques for monitoring and modeling shoreline evolution to support coastal risk management

The precise delineation of coastal areas subject to past, present, and future erosive processes plays a fundamental role in coastal risk management. Within this framework, satellite data represent a valuable synoptic and multi-temporal information source. Therefore, this research integrated remote sensing and GIS techniques for mapping and modeling shoreline evolution through time. Long-term shoreline's proxy rates of advance and retreat were determined using Landsat data from the mid-1980s to 2011 and subsequently, a short-term scenario (3 years) was predicted and validated. Two different coastal environments, Oceanic and Mediterranean, were investigated. In the first, different proxies were analyzed, thereby enabling a multi-proxy analysis. Findings showed that the method provided more accurate results in higher energy environments (Oceanic) and where the coastline is not urbanized. Results also highlighted the importance of performing multi-proxy analyses in given study areas, to more reliably define shoreline modeling. Importantly, during the analyses, particular attention was given to assessing uncertainty, which is crucial when outcomes of scientific research are considered for management

Analysis of Hydro-meteorological Monitoring Data Collected in Different Contexts Prone to Shallow Landslides of the Oltrep\uf2 Pavese

This work presents the results of the continuous monitoring of two slopes of the OltreP\uf2 Pavese (northern Apennines, north-western Italy), representative of different contexts usually affected by shallow landslides. The first monitored site is representative of high gradient slopes with silty soils. The second one represents slopes with low-medium slope gradient and clayey soils. Hydrological monitoring allowed to identify the responses of the soils to different rainy and dry periods, focusing in particular on conditions which could predispose landslide triggering. As demonstrated by monitoring and by slope stability analyses though a simplified physically-based model, increase in pore water pressure during most intense rainfalls in wet periods, sometimes with development of perched water tables, can promote slope instability

Assessing the daedalus sensor's performance by means of spectral mixture analysis in the Migliarino, San Rossore, Massaciuccoli Regional Park (Italy)

Coastal areas represent relevant zones for environmental monitoring. They are characterized by several habitats that coexist and interact in a condition of dynamic equilibrium. Moreover they are sites of human settlements and important economic and commercial activities. Therefore, an accurate environmental characterization of these complex systems require a large amount of information and different levels of analysis. To date, the contribution by remote sensing to study coastal zones is widely accepted as it provides high quality tools and products to investigate and monitor these fragile ecosystems. In this framework, the aim of this work is to test the performance of the multispectral Daedalus Airborne Thematic Mapper (ATM-2) sensor for the interpretation and analysis of geo-environmental features of the Migliarino, San Rossore, Massaciuccoli Regional Park's coastal area