GNGTS 2014 - Atti del 33° Convegno Nazionale

of salt water and the relationship with the sweet water. 3D models obtained by the inversion also showed seasonal variation (in time) of these relationships. Analyzing the three models (Fig. 2) it is possible to notice variations of resistivity very small (a) 4,36-31,2 Ωm; b) 4,66 – 30,36 Ωm; c) 7,45 – 32,7 Ωm).The low resistivity zone (Fig. 3), located in the lower and side part of the models, is interpreted as salt water related to marine intrusion. The middle sector of the models presents resistivity values compatible with the fresh aquifer. In detail, it is possible to observe changes between the volumes of brackish water and fresh-water during the spring and autumn seasons. In particular, the results highlight lower resistivity values in autumn (October 2013) in the shallow sector, ascribed to an increase of salt intrusion. This phenomenon is attributed to a lower contribution of fresh water in the aquifer of the plain due to the reduction of rainfalls during the summer season. The comparison, instead, with the two resistivity models acquired in May 2013 and 2014 showed no significant changes. The results of this study have led to a reconstruction of a three-dimensional model of the water bodies in the areas of flat inorder tounderstand the extent of the phenomenonof saltwater intrusion in time and space, resulting in qualitative and quantitative analysis of the volume of water used. This analysis shows that the shallow fresh-water should not be used because the pumping could determine greater intrusion of sea water, not allowing the accumulation of fresh water necessary in the natural suction of native species of plants. This monitoring program, supported by a careful management of resources, would prevent the worsening of the intrusion of the wedge with a difficult chance to return to the initial equilibrium conditions. Acknowledgements. The authors wish to thank Dr. Paolo Bonasoni, Scientific Responsible of I-AMICA project (High technology infrastructure for Integrated Climatic-Environmental monitoring), PON a3_00363. In addition, the authors wish to thank Paolo Scotto di Vettimo, Michele Iavarone, Dr. Rodolfo Baculo and Dr. Ivan Granata, for their help during data acquisition. References Al-Sayed E.A., El-Quady G.; 2007: Evaluation of sea water intrusion using the electrical resistivity and transient electromagnetic survey: case study at Fan of Wadi Feiran, Sinai; Egypt. EGM 2007 International Workshop, Italy. Barlow P.M.; 2003: Groundwater in fresh water-salt water environments along the Atlantic seaboard. Circular 1262 USGS. Fig. 2 – 3D ERT tomography models determined for different periods: a) May 2013; b) October 2013; c) May 2014. Fig. 3 – 3D resistivity contour plot referred to salt water (resistivity 4-15 Ωm): a) May 2013; b) October 2013; c) May 2014. 204 GNGTS 2014 S essione 3.2