Maria Teresa Perri

Hydrogeophysical characterization and monitoring of the hyporheic and riparian zones: The Vermigliana Creek case study

The hyporheic and riparian zones are critical domains in a river ecosystem since they mediate the interactions between surface water and groundwater. These domains are generally strongly heterogeneous and difficult to access; yet their characterization and monitoring still rely mostly on hard-to-perform invasive surveys that provide only point information. These well-known issues, however, can be overcome thanks to the application of minimally invasive methods. In this paper, we present the results of the hydrogeophysical characterization of the Vermigliana Creeks hyporheic and riparian zones, performed at an experimental site in the Adige catchment, northern Italy, by means of electrical resistivity tomography (ERT), distributed temperature sensing (DTS), and hydrological modeling. A major advancement is given by the placement of electrodes and of an optical fiber in horizontal boreholes at some depth below the river bed, put in place via directional drilling. The results of this static and dynamic (time-lapse) geophysical characterization identify the presence of two subdomains (the sub-riverbed and the left and right banks) and define the water flow and solute dynamics. The ERT information is then used, together with other hydrological data, to build a 3D subsurface hydrological model (driven mainly by the watercourse stage variations) that is calibrated against local piezometric information. A solute transport model is then developed to reproduce the variations observed in the dynamic geophysical monitoring. The results show good agreement between ERT data and the model outcome. In addition, the transport model is also consistent with the temperature data derived from DTS, even though some slight discrepancies show that the heat capacity of the solid matrix and heat conduction cannot be totally neglected.

A multi-disciplinary study of deformation of the basaltic cover over fine-grained valley fills: a case study from Eastern Sardinia, Italy

The Pliocene to Early Pleistocene volcanic activity which generated the basaltic plateau of the Orosei-Dorgali area in Eastern Sardinia led to the disruption of the local hydrographic network by damming some tracts of the fluvial valleys incised in the granite basement. This resulted in the formation of lacustrine basins, whose fine-grained fills were partly interfingered and eventually covered by younger lava flows. In the SW part of the plateau, close to the Galtellì village, a number of unknown depressions, locally named “Paules,” were formed. In order to reconstruct their subsurface structure, two electrical resistivity tomography surveys were carried out across these depressions. The geophysical results, which demonstrate the existence of a disrupted layered system, were used to build a numerical geomechanical model that suggest the depressions originated by local collapses of the basaltic cover due to the compaction of the underlying fine-grained valley fills.

Quantitative Interpretation of Time-lapse MALM Measurements During a Saline Tracer Injection in an Alluvial Aquifer

This study presents the results of a saline tracer test conducted on an unconfined alluvial aquifer placed in the Alento River Valley (Campania region, South-Western Italy) and monitored by Mise-a-la-Masse measurements. The aim of this test is the investigation of groundwater flow field by a time-lapse analysis. The work first introduces the local hydrogeology of the investigated system and the experimental set-up. The results of the geophysical tracer test are then described and followed by the discussion of several simulations conducted on a 3D electrical model of the system. Finally, the comparison between real and simulated datasets is discussed in order to highlight advantages and limitations of Mise-a-la Masse technique when applied for hydrogeological purposes.

Non Invasive Characterization of a Small Mountain Catchment for Hydrological Purposes

The description of catchment response during storms and droughts is a fundamental issue in geosciences. In particular, the subsoil characterization is a crucial step towards understanding hydrological processes in mountain regions and for the calibration of models that can describe and predict water flow patterns. Non-invasive (or minimally invasive) geophysical techniques are helpful to provide spatially extensive data, whereas traditional borehole-based sampling is often limited because of the localized nature of such measurements and the disturbance induced to samples. The aim of this study is the characterization of a small-scale mountain catchment to obtain detailed knowledge about its hydrogeological and hydrological system behavior. The experimental site is located at Carre near Vicenza (North-Eastern Italy) in the pre-alpine hill region named Bregonze. For this purpose we used several geophysical techniques: Electrical Resistivity Tomography (ERT), Seismic refraction survey, Seismic surface wave investigation. The former techniques highlight the shallowest subsoil discontinuities (from 0 to 2 m); the latter one provides knowledge about the underlying layers and the associated lateral heterogeneities. The combination of geophysical methods can help characterize a complex hydrogeological system, at least from the structural viewpoint.