Determination and Evaluation of Saltwater Intrusion on Bafra Plain: Joint Interpretation of Geophysical, Hydrogeological and Hydrochemical Data

Abstract

Saltwater intrusion and its spatial distribution using a multidisciplinary approach were investigated on the northeast coast of Bafra Plain, which is one of the most important delta plains in Turkey. Intensive agricultural activity in the study area, which supplies the local and international market with agricultural products, is increasing the importance of this ecosystem. Even the groundwater potential and supply are high; the main problem is the groundwater degradation due to salinization. Moreover, local lithological, tectonic and hydrological complexities increase the uncertainty in the interpretation of the collected (chemical, geophysical, etc.) data, providing an inaccurate geomodel. Specifically, in the study area, there are mixtures of freshwater/saltwater aquifers and geological units containing clay lenses/thin layers and fine-grained alluvium. At the same time, these geological formations have similar resistivity responses, and the ambiguity of the collected electric and electromagnetic geophysical data is high. Therefore, a third geophysical method (seismic refraction), which is sensitive to different physical parameters to constrain the uncertainty in the interpretation, was used. In this study, the salinization of Bafra Plain and complex aquifer system was revealed with the combined use of direct-current resistivity and transient electromagnetic data constrained by seismic refraction data and guided by hydrogeological and hydrochemical data. Using information obtained from multidisciplinary study, we inferred that the intrusion is monitored inland up to 3.5 km. The intrusion is traced after approximately the first 10 m depth in the central part of the plain. Additionally, in some areas, it was concluded that the intrusion is interrupted by clay lenses. Also, drainage channels constructed in the plain have brought soil salinization under control but have not completely succeeded in controlling the saltwater intrusion into the deeper aquifer. The saltwater intrusion can move more inland if groundwater pumping is not controlled, especially in areas close to the river.