Comparison of geoelecteric, electromagnetic and Verruijt equations for determination of the subsurface saline and fresh interface in coastal aquifer

Due to the downfall of groundwater table caused by the drilling of several illegal wells, unlimited groundwater extraction and sea water intrusion, the precise identification of saline groundwater zone in shorelines is highly crucial. This research was conducted to compare three different methods (geoelecteric, electromagnetic, Verruijt equations) to detect the interface of subsurface fresh and saline water in western and eastern part of Babolsar city, northern Iran. Due to the insufficient hydrogeological data in the study area such as occurred spread across the Mazandaran province, the Verruijt equations could not predict the saline and fresh water interfaces precisely, but the geoelecteric method showed relatively higher precision. The results of both studied sites (eastern and western part of Babolsar city) were approximately identical. The electromagnetic method with the highest significant correlation (R=0.97 and 081; CCC=0.95 and 0.80) and the lowest errors (ME=-2.22 and 0.28; RMSE=4.83 and 1.96) respectively in the western and eastern part of the area and also the insignificant t-test was identified as the best approach for accurate prediction of the saline and fresh water interfaces. Considering the insufficient hydrogeological data in shoreline of Mazandaran province and due to the high performance, rapid determination and more reliability of the electromagnetic-based data, this method could be recommended for determination of the subsurface saline and fresh interface in coastal aquifer.