Electrical Resistivity Tomography for Coastal Salt Water Intrusion Characterization along the Ionian Coast of Basilicata Region (southern Italy)

The first results of a research activity focused on the characterisation of the salt water intrusion along the Ionian coast of the Basilicata region (Southern Italy) are shown and discussed in this study. Along the coast there are many Sites of Community Interest (SCI) subjected to a strong incidence of human activities mainly linked to agriculture and tourism. Primary and secondary salinity of soil are linked to natural factors such as the climate, natural drainage patterns, topographic features, geological structure, distance to the sea and to the indiscriminate exploitation of the soil and groundwater resources. The approach based on the Electrical Resistivity Tomography (ERT) has been adopted to obtain high-resolution electrical images which allow to identify and delineate the geometry of litho-stratigraphic limits, by resistivity contrasts. Then, ERT represents an optimal tool for better reconstructing the geometry of the sea water intrusion front and mapping the areas characterized by a high level of salinization. In fact, the presence of seawater strongly reduces the resistivity values. For this reason it is necessary to evaluate if the contrast between the zones affected by saltwater intrusion and the geological layers is significant and if it can be detectable. In this frame, some soil samples have been analyzed using chemical physical techniques in order to validate the geophysical measurements. Five electrical tomographies were performed along the coast close to the rivers Bradano, Basento, Cavone and Agri with multielectrode acquisition system in a WennerSchlumberger array configuration with electrodes spacing on the surface of 10.00 meters. Resistivity tomographic images, in general, have shown a decrease of resistivity by going deeper and towards the Ionian Sea coastline, and, in some zones along the coast they have highlighted the presence of a top layer of greater thickness with high resistivity values. These evidences indicate that anyway the process of saline intrusion is present, but it has not yet affected the layer of soil which is generally explored by the roots of plants, and as a matter of the fact, these areas have a good vegetation cover. On the whole, the results obtained in this study suggest that the ERT can be a suitable support tool for the activities of planning and management, which are fundamental for the preservation of coastal areas of great environmental, economic, social and cultural relevance.