A Study of the Correlation Between Electrical Resistivity and Matric Suction for Unsaturated Ash-Fall Pyroclastic Soils in the Campania Region (Southern Italy)

In the territory of the Campania region (southern Italy), critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the Mt. Somma-Vesuvius volcano and deposited along the surrounding mountain ranges. In this paper, an integration of engineering-geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the Sarno Mountains (Salerno and Avellino provinces, Campania region). The laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content. From the matching of the experimental data, a direct relationship between electrical resistivity and matric suction is retrieved for the investigated soil horizons typical of a ash-fall pyroclastic succession. The obtained relation turns out to be helpful in characterizing soils up to close saturation, which is a critical condition for the trigger of slope failure. In such a regime, the water content and the matric suction have small variations, while electrical resistivity variations can be appreciated in a larger range of values. For this reason, besides suction measurements on very small soil volumes through classical tensiometers, our analyses suggest the direct monitoring of in-situ electrical resistivity values as an effective tool to recognise the hydrological state of larger and more representative soil volumes and to improve early warning of dangerous slope movements.Comment: 23 pages, 10 figures, 2 table

Groundwater recharge estimation in karst aquifers of southern Apennines (Italy) by integration of remotely sensed data

Karst aquifers, actual evapotranspiration, groundwater recharge, remote sensing data, southern Italy

MULTI-SCALE ASSESSMENT OF GROUNDWATER VULNERABILITY TO POLLUTION: STUDY CASES FROM CAMPANIA REGION (SOUTHERN ITALY)

In the Campania region (southern Italy), assessment of groundwater vulnerability is an important factor to be tackled for a proper management of risk to aquifer pollution, which is fostered by both high dependence of aqueduct systems on groundwater resources and the widespread agricultural and urbanized land uses of the territory. The different physiographic, geological and hydrogeological conditions of the region, coupled with high anthropic pressure, make such assessment complex to be dealt with, but at the same time mandatory to be accomplished. The proposed study has been developed into the framework of the “Campania Trasparente” project, which has been funded by the regional government to assess environmental factors controlling the quality of agricultural and livestock food productions. Specifically, it belongs to the research topic regarding the assessment of groundwater quality, with a special focus on the assessment of groundwater vulnerability. In this research a multi-scale approach for the assessment of groundwater vulnerability is carried out in order to propose suitable methods depending on extension of territory to be studied and related types and spatial density of available data. Scales considered were a) regional, including the whole Campania region; b) intermediate, identified with that of a single representative aquifer; c) site-specific, or local, related to a portion of aquifer for which a high spatial density of data is available.The applied methods were chosen among the many known in literature and adapted to the specific study cases. At the regional scale, the parametric SINTACS method (CIVITA & DE MAIO, 2000) has been applied to the whole region and adapted to types and spatial density of available data. At the intermediate scale, or aquifer scale, the Mt. Terminio karst aquifer was chosen as representative for the application of different parametric methods, also specifically designed for karst aquifers. At the site-specific scale, a representative sector of a shallow alluvial aquifer, located in the adjoining Casalnuovo di Napoli-Volla municipalities, in the Campania plain, at the eastern border of the city of Naples, has been studied by numerical modeling for the estimation of travel time of nitrate pollutant through the vadose zone. The obtained results can be conceived as useful for supporting a proper territorial planning aimed at the management of risk to pollution of groundwater resources

Susceptibility mapping of shallow landslides inducing debris flows: a comparison of physics-based approaches

The assessment of timing and potential locations of rainfallinduced shallow landslides through mathematical models represents a challenge for the assessment of landslide hazard, especially in cases with limited or not available data. In fact, modeling slope hydrological response and stability requires accurate estimates of unsaturated/saturated hydraulic and geotechnical properties of materials involved in landsliding, as well as climate and topography. Such aspect is relevant for the prediction of location and timing of landslide events, which is greatly needed to reduce their catastrophic effects in terms of economic losses and casualties. To such a scope, we present the comparison of results of two physics-based models applied to the assessment of susceptibility to shallow rainfall-induced landslides in Valtellina region (northern Italy). The analyses were carried out considering effects of availability, resolution and type of data concerning spatial distribution, thickness and properties of soils coverings. For such a scope, the Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS) and the Climatic Rainfall Hydrogeological Modeling Experiment (CHRyME) models were considered. The study emphasizes issues in performing distributed numerical slope stability modeling depending on the availability of spatially distributed soil properties which hamper the quality of physic-based models. Further analyses aimed at the probabilistic assessment of landslide spatial distribution, related to a specific value of rainfall threshold, can be considered as potentially applicable to multi-scale landslide hazard mapping and extendable to other similar mountainous frameworks

Evaluation of the applicability of sediment transport models to dam filling prediction in different Italian geological contexts

Artificial reservoirs are crucial infrastructures, since they allow for the management of the water resource they store and for their role in the hydroelectric production. Water is modulated and stored inside artificial basins built upstream of the dams for hydroelectric, industrial, drinking, irrigation, and flood mitigation purposes. However, as time passes, the deposition of solid material, transported by rivers flowing into the reservoir, reduces its storage capacity. In this work, a novel physicallybased erosion and sediment transport model developed by Politecnico di Milano (SMART-SED) is used to estimate dam filling in different Italian geological contexts. The present model differs from others in the literature since it can automatically detect drainage zones and it works at a basin scale, requiring few input parameters that can be easily downloaded from global or government databases. Moreover, it is based on robust and unconditionally stable numerical techniques, and it guarantees the mass conservation. The proposed model was applied to four watersheds, two in the Southern Alps and two in the Southern Apennines, with catchment areas ranging from 5 to 48 km2. After the model calibration on the local geological context, a validation of the obtained results was accomplished considering different time intervals and the available sediment filling data. It was observed that the SMART-SED model, initially developed for the evaluation of fluvial hazard and of sediment transport in mountainous areas, was also suitable for the estimation of dam filling. Results indeed show a precise approximation of the order of magnitude of the cumulative sediment volume produced inside the catchments and transported to the water basins. In the framework of a complex problem affecting the production of “clean” energy in a changing world, SMART-SED could become a useful tool also for dam management

Hydrological regimes in different slope environments and implications on rainfall thresholds triggering shallow landslides

Assessing hazard of rainfall-induced shallow landslides represents a challenge for the risk management of urbanized areas for which the setting up of early warning systems, based on the reconstruction of reliable rainfall thresholds and rainfall monitoring, is a solution more practicable than the delocalization of settlements and infrastructures. Consequently, the reduction in uncertainties afecting the estimation of rainfall thresholds conditions, leading to the triggering of slope instabilities, is a fundament task to be tackled. In such a view, coupled soil hydrological monitoring and physics-based modeling approaches are presented for estimating rainfall thresholds in two diferent geomorphological environments prone to shallow landsliding. Based on the comparison of results achieved for silty– clayey soils characterizing Oltrepò Pavese area (northern Italy) and ash-fall pyroclastic soils mantling slopes of Sarno Mountains ridge (southern Italy), this research advances the understanding of the slope hydrological response in triggering shallow landslides. Among the principal results is the comprehension that, mainly depending on geological and geomorphological settings, geotechnical and hydrological properties of soil coverings have a fundamental control on the timing and intensity of hydrological processes leading to landslide initiation. Moreover, results obtained show how the characteristics of the soil coverings control the slope hydrological response at diferent time scales, making the antecedent soil hydrological conditions a not negligible factor for estimating landslide rainfall thresholds. The approaches proposed can be conceived as an adaptable tool to assess hazard to initiation of shallow rainfall-induced landslides and to implement early-warning systems from site-specifc to distributed (catchment or larger) scales

Application of structure from motion photogrammetry to multi-temporal geomorphological analyses: case studies from Italy and Spain

The study of the geomorphological evolution of landscapes is one of the most important tasks needed for assessing the natural and man-made geohazards and risks affecting a territory. In the last two decades, instrumental and computational advances have allowed the development of effective remote sensing methodologies, such as those based on Synthetic Aperture Radar (SAR) Interferometry or change detection techniques (Tomás & Li, 2017). These techniques have enhanced the possibilities of making geomorphic observations and modelling. Specifically, Earth Observations (EO) techniques using airborne or satellite platforms have increased the ability to map and monitor geomorphological processes. In such a framework, historical landscape data, such as those available from aerial photographs taken since the early 1940s, are key instruments for studying the geomorphological evolution of a territory. In this work, the application of the Structure from Motion (SfM) technique to analyse the geomorphological evolution of sample areas by historical aerial photos is tested, examined, and discussed. Towards this aim, multi-temporal analysis by means of three-dimensional (3D) land models of four test areas reconstructed through the application of the SfM technique using available aerial images was performed. Although it is well known that SfM requires a considerable number of digital images and a significant overlap between them, the challenge of this approach was to reconstruct 3D land models using a reduced set of analogical aerial photos for satisfactory results. The resulting 3D reconstructions succeeded in recognizing and studying the geomorphological evolution of the test areas, represented by: a) a region in southern Italy affected by landslides; b) a territory in central Italy affected by badland-type intense erosional phenomena; c) a sector in northwestern Italy with open-pit mining activity; and d) a coastal zone affected by changes in its coastline. Despite some disadvantages that arose during the application of the SfM technique, the proposed methodology has been shown to be useful for geomorphological analysis. This can be considered an alternative to the use of analogical and digital stereoscopic techniques to recognize geomorphological shapes and analyse Earth surface evolution and the effects of different anthropic activities.Part of this work was supported by the University of Alicante (vigrob-157 Project, GRE14-04 Project and GRE15-19 Project), the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), the State Agency of Research (AEI) and the European Funds for Regional Development (FEDER) (projects TEC2017-85244-C2-1-P, ESP2013-47780-C2-2-R and TIN2014-55413-C2-2-P) and the Spanish Ministry of Education, Culture and Sport (project PRX17/00439)

Physically based estimation of rainfall thresholds triggering shallow landslides in volcanic slopes of Southern Italy

On the 4th and 5th of March 2005, about 100 rainfall-induced landslides occurred along volcanic slopes of Camaldoli Hill in Naples, Italy. These started as soil slips in the upper substratum of incoherent and welded volcaniclastic deposits, then evolved downslope according to debris avalanche and debris flow mechanisms. This specific case of slope instability on complex volcaniclastic deposits remains poorly characterized and understood, although similar shallow landsliding phenomena have largely been studied in other peri-volcanic areas of the Campania region underlain by carbonate bedrock. Considering the landslide hazard in this urbanized area, this study focused on quantitatively advancing the understanding of the predisposing factors and hydrological conditions contributing to the initial landslide triggering. Borehole drilling, trial pits, dynamic penetrometer tests, topographic surveys, and infiltration tests were conducted on a slope sector of Camaldoli Hill to develop a geological framework model. Undisturbed soil samples were collected for laboratory testing to further characterize hydraulic and geotechnical properties of the soil units identified. In situ soil pressure head monitoring probes were also installed. A numerical model of two-dimensional variably saturated subsurface water flow was parameterized for the monitored hillslope using field and laboratory data. Based on the observed soil pressure head dynamics, the model was calibrated by adjusting the evapotranspiration parameters. This physically based hydrologic model was combined with an infinite-slope stability analysis to reconstruct the critical unsaturated/saturated conditions leading to slope failure. This coupled hydromechanical numerical model was then used to determine intensity–duration (I-D) thresholds for landslide initiation over a range of plausible rainfall intensities and topographic slope angles for the region. The proposed approach can be conceived as a practicable method for defining a warning criterion in urbanized areas threatened by rainfall-induced shallow landslides, given the unavailability of a consistent inventory of past landslide events that prevents a rigorous empirical analysis

Hydrogeological and hydrogeochemical monitoring in the Cumae archaeological site (Phlegraean Fields, southern Italy)

Phlegraean Fields, hydrogeological model, hydrochemical facie