GALDIT-SUSI a modified method to account for surface water bodies in the assessment of aquifer vulnerability to seawater intrusion.

The salinization of coastal aquifers is one of the major environmental issue worldwide. Overexploitation is the most common reason of salinization, since it generates a piezometric inversion, which in turn leads to groundwater flow from the coast towards inland. This also occurs in water bodies connected to the sea like lagoons, rivers, torrents and wetlands. In this study, a modification of the GALDIT method including "SUperficial Seawater Intrusion (SUSI)" is proposed. Six new parameters were added to the classical ones. The analytical hierarchy process and the sensitivity analysis were performed for weights definition and validation of the proposed GALDIT-SUSI method. Two study areas, with different characteristics were chosen for the application of both methods: the coastal area of Epanomi (Greece) and the Po River lowland (Italy). The application of the standard GALDIT in both sites showed a poor discrimination of the vulnerability to seawater intrusion, confining it only in proximity to the coastline. Conversely, GALDIT-SUSI divided the two sites in five classes of vulnerability ranging from very low to very high, stressing the higher vulnerability of lagoons and wetland for Epanomi and lagoons and rivers for the Po River lowland. GALDIT-SUSI is easy to apply and versatile, since it can be adapted to the specific hydrogeological setting of the area of interest. Moreover, GALDIT-SUSI can be further improved to deal with other salinization mechanisms.