GEOPHYSICAL INVESTIGATIONS AT NAFPLION CITY, GREECE. HYDROGEOLOGICAL IMPLICATION

The application of selected geophysical methods within the framework of an Urban Geology investigation program performed by IGME at Nafplion city, contributed to the overall geo-scientific characterization of the study area. The methodology adopted included the application of Time Domain Electromagnetic, Electrical resistivity tomography, Gravity and Seismic Crosshole surveys. The results of the geophysical investigation provided quantitative information regarding the distribution of seawater intrusion in the area and determined factors controlling its extent within the investigated region. The intrusion may occur in three distinct horizons. The first within the shallow unconfined aquifer within the top 12 meters of fluvial deposits showing values of electrical conductivity in the range of 1 and 4 Siemens/m, corresponding to TDS values between 5000 and 20000 mg/L, as determined by the TEM surveys. Lower conductivity values between 0.3 and 1 Siemens/m are found within the second aquifer occurring between 15 and 45 meters. Similar order of conductivity values are found within the deeper horizon, lying below 45 meters depth, attributed also to seawater intrusion mainly in carbonate formations. Areas of fresh groundwater, were delineated by a combination of TEM, ERT and gravity methods. These areas are structurally controlled by faults and the presence of impermeable flysch overlying the limestone formation.