GNGTS 2014 - Atti del 33° Convegno Nazionale

Sea water intrusion in the water table can cause significant worsening in vegetation status. A likely related soil salinization would cause detrimental environmental and socio- economic impacts. Hence, monitoring the sea water intrusion represents a priority for the safeguard of coastal areas. Identify changes in the freshwater-saltwater interface position can be a useful element for the rationalization of water resources and to guide the choice of use of these areas. Among the geophysical method applied for the location and movement of saltwater intrusion, best results were obtained by electrical methods (Al-Sayed and Al- Quady, 2007; Chitea et al. , 2011). Many hydrological processes can be expected to provide significant contrasts in resistivity, consequently, Electrical Resistivity Tomography (ERT) has been adopted as a tool for new research within the hydrology field. Previous workers have demonstrated the ability of ERT to visualize hydrological structure within laboratory cores (Binley et al. , 1996a, 1996b), monitor fluid or contaminant migration at the field scale (Daily et al. , 1992, 1995; Schima et al. , 1993), and to ascertain the efficiency of new contaminant remediation processes (Daily and Ramirez, 1995; LaBrecque et al. , 1996). This paper outlines the results of a 3D ERT experiment obtained in the coastal alluvial plain of the Volturno river to assess changes in the freshwater-brine interface. The main aim was to investigate spatial and temporal variations of groundwater salinity. Acquisitions have been carried out in the months of May and October 2013 and in May 2014. This acquisition has allowed to obtain a monitoring 4D salt wedge in a “volume” specific subsurface. Geological and hydrogeological setting. The investigated area is located in the northern sector of the Campania Plain, near to the mouth of Volturno river (Fig. 1). It is the main river in southern Italy: it crosses Molise and Campania regions, for a total length of 175 km with a watershed of 545 km 2 . The Volturno is characterized by minimum flow in summer and overflow in autumn and spring. The area is characterized by a sub-horizontal morphology with main level similar to the sea level. The geomorphology of the Campania Plain corresponds to a structural depression which is formed during the Lower Pleistocene. Until to 130.000 years ago the plain of the Volturno was regulated by a phenomenon of subsidence (Cinque and Romano, 2001) and fell in a marine environment. Afterwards, the area was affect by pyroclastic fall-out and flow from Campi Flegrei and Roccamonfina (Ortolani and Aprile, 1978, 1985). In general, the stratigraphic sequence of the area is characterized by continental deposits (Romano et al. , 1994; Corniello et al. , 2010), a surface layer of silt and clay, an underlying sand layer and a basal layer characterized by clayey peat and reworked pyroclastics. River-borne sediments discharged in the sea in the past caused the river mouth to prograde. However, in the last 150 years, the latter has progressively retreated due to the dams built along the river and the extraction of gravel from the river bed (Biggiero et al. , 1994). All these sediments have a lenticular pattern that determines a groundwater flow in layered aquifers. This determines, in conditions of excessive pumping and for a greater thickness of the sedimentary body that houses the sweet aquifer, a mixture of fresh water with the salt water. In Fig. 1 – Location of the study area. Red lines are the 3D ERT grid. 202 GNGTS 2014 S essione 3.2