DC and FDEM salt wedge monitoring of the Po di Goro river (Italy).

The global warming is affecting the rising seas, which increase the saltwater contamination of the coastal zone in terms of intrusion and penetration in the delta system. The delta systems are characterized by complex dynamic between freshwater coming from continent and saltwater. The hydrodynamic system is greatly affected by the problem of climate change producing a scarce recharge of the aquifers and an increase of the upstream of the mixing zone in the surface waters. These conditions can hinder the water use for irrigation purpose leading to salinization of soils. This summer the Po River underwent a large saltwater intrusion crisis endangering the sustainability of the freshwater resources. The saline wedge in the Po Delta area defined salinisation of groundwater and the soil. These phenomena allow for the active ingression of seawater from the east because the hydraulic head is not sufficient to avoid water to flow inland from the sea. In order to define the water quality, the electrical conductivity (EC) is one of the typical used chemical-physical parameters. However, a common probe defines a punctual acquisition and, therefore, it is time consuming to make a monitor along a long river (> 50km), such as the Po di Goro, that is one of the Po River branches. The research group defined two fast geophysical approach for the monitoring of the saltwater penetration and intrusion. The FDEM method was used to detect the saline wedge in the river and the Electrical Resistivity Tomography was applied to monitor the hydrodynamic iteration between the river and the subsoil around the riverbanks. Two geophysical field activities were planned before and after the salt penetration crisis in the Po River, defined in the last summer. In detail, two ERTs and two long FDEM profiles were carried out along the Po di Goro river. Moreover, a “moving boat” approach with a multilevel EC probe was applied to join the acquired geophysical data set. The ERT sections highlighted how the salty water in the river contaminated the surrounding subsoil. The FDEM data sets defined the hydrodynamic of the saltwater wedge in the river detecting the salty plume front. These results highlight the great potential of the proposed geophysical approach to monitor the saline plume during crisis periods.