Galgaro, Antonio

Riassunto Attraverso l’indagine geoelettrica è stata eseguita una prima valutazione dell’estensione dell’intrusione salina marina e lagunare nel settore meridionale del comprensorio veneziano. Nel settore costiero, caratterizzato da dune e cordoni litoranei, è presente una falda freatica con acqua “dolce” fino ad una profondità di anche una decina di metri e l’intrusione salina coinvolge i terreni sottostanti fino ad oltre 70 metri. Nell’entroterra, la soggiacenza del territorio rispetto al livello marino, i pompaggi con idrovore e la rete idrografica pensile in comunicazione col mare sono fattori che riducono a pochi metri, ed in alcune zone annullano, lo spessore della falda dolce superficiale e consentono al cuneo salino di raggiungere la base dei terreni coltivati. Abstract A preliminary evaluation of the salt water intrusion in coastal aquifers of the southern Venetian region, is here made using geoelectical investigation. The results of the analyses show that the two dimensional extent of the saline contamination is mainly related to the geomorphology of this area. In the littoral sector, characterized by a mean ground elevation of two meters above mean sea level (sand dunes and paleolittoral strips), a phreatic fresh water body is present and salt water contamination involves aquifers and aquitards from 10 to 70 m deep. In the inland, the ground level is about 2-3 m below mean sea level; the water pumping in the reclaimed lands and the marine water seepage in the rivers during high tides are among the factors that seriously reduce the fresh water body and that allow salt water to contaminate the agricultural soils.

Two MatlabTM software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude too far points from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations or rapid landslide collapses, and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided.

The internal structures of some surviving sand dunes and the ancient shore-lines along the coast south of Venice have been investigated integrating Ground Probing Radar (GPR) profiles, Vertical Electrical Soundings (VES) and water conductivity measurements in some boreholes. The GPR penetration depth has been limited (4-5 m,using a 400 MHz antenna) by the high conductivity of salt water saturating pores of the shallow sediments. On the other hand, the excellent spatial resolution of the radar survey provided an estimate of internal dune bedding features, such as cross lamination and forwarding ancient covered coast-lines dated in the Thirties. The interpretation of the data, in particular along one line 360 m long intercepting a sizable sand-dune bank, seems to offer clues to the evolutional history of the coast line and the depth of transition from fresh-water to brackish-salt water. The water table was detected with electrical measurements and direct observations in boreholes, whereas the transition between fresh and salt water (brackish water) was pointed out indirectly by the high energy absorption and total back-reflection of the EM waves, encountered at this boundary, and directly by the strong decrease in VES resistivity values.

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Terrestrial Laser Scanner (TLS) is an active instrument widely used for physical surface acquisition and data modeling. TLS provides both the geometry and the intensity information of scanned objects depending on their physical and chemical properties. The intensity data can be used to discriminate different materials, since intensity is proportional, among other parameters, to the reflectance of the target at the specific wavelength of the laser beam. This article focuses on the TLS-based recognition of rocks in simple sedimentary successions mainly constituted by limestones and marls. In particular, a series of experiments with an Optech ILRIS 3D TLS was carried out to verify the feasibility of this application, as well as to solve problems in data acquisition protocol and data processing. Results indicate that a TLS intensity-based discrimination can provide reliable information about the clay content of rocks in clean outcrop conditions if the geometrical aspects of the acquisition (i.e. distance) are taken into account. Reflectance values of limestones, marls and clays show, both in controlled conditions and in the field, clear differences due to the interaction of the laser beam (having a 1535 nm wavelength) with H2O- bearing minerals and materials. Information about lithology can be therefore obtained also from real outcrops, at least if simple alternation of limestones and marls are considered. Comparison between reflectance values derived from TLS acquisition of an outcrop and the clay abundance curves obtained by gas chromatography on rock samples taken from the same stratigraphic section shows that reflectance is linked by an inverse linear relationship (correlation coefficient r = −0.85) to the abundance of clay minerals in the rocks. Reflectance series obtained from TLS data are proposed as a tool to evaluate the variation of clay content along a stratigraphic section. The possibility of linking reflectance values to lithological parameters (i.e. clay content) could provide a tool for lithological mapping of outcrops, with possible applications in various fields, ranging from petroleum geology to environmental engineering, stratigraphy and sedimentology.

The assessment of potential radon-hazardous environments is nowadays a critical issue in planning, monitoring, and developing appropriate mitigation strategies. Although some geological structures (e.g., fault systems) and other geological factors (e.g., radionuclide content, soil organic or rock weathering) can locally affect the radon occurrence, at the basis of a good implementation of radon-safe systems, optimized modelling at territorial scale is required. The use of spatial regression models, adequately combining different types of predictors, represents an invaluable tool to identify the relationships between radon and its controlling factors as well as to construct Geogenic Radon Potential (GRP) maps of an area. In this work, two GRP maps were developed based on field measurements of soil gas radon and thoron concentrations and gamma spectrometry of soil and rock samples of the Euganean Hills (northern Italy) district. A predictive model of radon concentration in soil gas was reconstructed taking into account the relationships among the soil gas radon and seven predictors: terrestrial gamma dose radiation (TGDR), thoron (220Rn), fault density (FD), soil permeability (PERM), digital terrain model (SLOPE), moisture index (TMI), heat load index (HLI). These predictors allowed to elaborate local spatial models by using the Empirical Bayesian Regression Kriging (EBRK) in order to find the best combination and define the GRP of the Euganean Hills area. A second GRP map based on the Neznal approach (GRPNEZ) has been modelled using the TGDR and 220Rn, as predictors of radon concentration, and FD as predictor of soil permeability. Then, the two GRP maps have been compared. Results highlight that the radon potential is mainly driven by the bedrock type but the presence of fault systems and topographic features play a key role in radon migration in the subsoil and its exhalation at the soil/atmosphere boundary.

RIASSUNTO Nelle aree costiere e perilagunari del comprensorio meridionale veneziano l'approvvigionamento idrico ha risentito in più occasioni degli effetti negativi dell'intrusione di acque marine e lagunari nel sottosuolo. Per valutare l'estensione e la gravità della contaminazione salina è stato condotto un primo studio in un’area fortemente interessata dagli effetti di tale fenomeno, che si ripercuotono pesantemente nell'attività agricola, turistico-alberghiera e industriale. Lo studio è stato condotto con l'utilizzo di sondaggi elettrici verticali (S.E.V.) e con determinazioni del tenore salino dell'acqua di pozzi freatici ed artesiani, nonché dei fiumi, canali e scoli della rete idrografica. I risultati delle indagini hanno evidenziato che il settore litoraneo e quello di entroterra presentano entità e modalità di propagazione della contaminazione salina differenti. Nella fascia litoranea, costituita principalmente da sabbie di dune eoliche e di antichi cordoni litoranei, risiede una lente di acqua dolce con uno spessore di anche una decina di metri. Sottostante questa lente, la contaminazione salina può raggiungere i 70 metri di profondità. Nel settore di entroterra e di margine lagunare invece, la salinizzazione del sottosuolo è favorita dalla critica situazione altimetrica del territorio e dall'attività di bonifica idraulica. Infatti la soggiacenza del piano campagna rispetto al livello del mare, i pompaggi delle idrovore e la dispersione di acqua marina dalla rete idrografica riducono a pochi metri o addirittura annullano lo spessore dell'acqua freatica dolce superficiale rendendo la situazione particolarmente grave specialmente quando In contaminazione salina coinvolge i terreni coltivati. ABSTRACT The aim of this study is the evaluation of the salt water intrusion extent in coastal aquifers of the Southern Venetian Region. The groundwater salinity contamination was obtained by combining geophysical investigations, such as Vertical Electric Soundings (V.E.S) and Conductibility, Temperature, depth (CTD) measures of water samples, with stratigraphical data. In particular, 41 V.E.S., obtained with a maximum distance between the electrodes ranging from 300 to 2000 m, and CTD data of 17 selected water samples taken in the rivers, channels and wells, were considered. The study shows that the two dimensional extent of the saline contamination is mainly related to different geomorphology of the littoral and of the inland sectors. The littoral sector is characterized by a ground elevation up to three meters above mean sea level. The dune belt and paleolittoral strip sand formations constitute a well-developed phreatic aquifer with a fresh water body, up to 10 meters deep, floating on the saline water. The salt water contamination involves the aquifers and the aquitards below the fresh water body down to a depth of 70 meters. Reclaimed land constitutes the inland sector; because its ground level is about 2-3 meters below the mean sea level water, pumping is required to maintain the water level below land surface. The critical ground elevation, the water pumping and the marine water seepage in the rivers during high tides are the factors that seriously reduce the size of fresh water body and allow the salt water contamination of the agricultural soils. The extension of the salt water contamination of the aquifer-aquitard system is here shown by a series of profiles crossing the littoral strip and the lagoon margin. The collected data, although not sufficient to illustrate the complex interaction of the contamination factors, allowed the evaluation of the size and extent of the salt water intrusion process and constitute the base for further detailed studies.

This work highlights the importance of the Geogenic Radon Potential (GRP) component originated by degassing processes in fault zones. This Tectonically Enhanced Radon (TER) can increase radon concentration in soil gas and the inflow of radon in the buildings (Indoor Radon Concentrations, IRC). Although tectonically related radon enhancement is known in areas characterised by active faults, few studies have investigated radon migration processes in non-active fault zones. The Pusteria Valley (Bolzano, north-eastern Italy) represents an ideal geological setting to study the role of a non-seismic fault system in enhancing the geogenic radon. Here, most of the municipalities are characterised by high IRC. We performed soil gas surveys in three of these municipalities located along a wide section of the non-seismic Pusteria fault system characterised by a dense network of faults and fractures. Results highlight the presence of high Rn concentrations (up to 800 kBq·m-3) with anisotropic spatial patterns oriented along the main strike of the fault system. We calculated a Radon Activity Index (RAI) along north-south profiles across the Pusteria fault system and found that TER is linked to high fault geochemical activities. This evidence confirms that TER constitutes a significant component of GRP also along non-seismic faults.

Assessment and mitigation of the risk induced by landslide activation need an appropriate phenomenon investigation, to obtain useful information about the failure processes. The first step is the complete kinematics characterization of the landslide ground surface, by evaluating the involved displacement and deformation patterns. A dense displacement field can be obtained from comparison of a series of multi-temporal observations performed by means of terrestrial laser scanning. Subsequently, the strain field can be computed from displacement vectors. In this paper, a modified least square technique is employed to compute the strain on the nodes of a regular grid (2D) approach) or on the points of a digital terrain model (3D) approach). Such a computation takes into account the displacements, their spatial distribution, as well as the measurement and modelling errors. A scale factor is introduced in order to emphasize the contributions of the experimental points on the basis of their distance from each computation point, and to recognize possible scale-depending behaviours. This method has been implemented in Matlab and applied on two landslides located in the northeastern Italian Alps (Lamosano and Perarolo di Cadore). The experiments show that different kinematics can be recognized, and the presence and influence of eventual discontinuities can be revealed