Combined ERT-TDEM measurements for studying submarine groundwater discharge (SGD) at Dor Beach, Israel

During last years, Dor Beach became a major test site for hydrogeological, geochemical and geophysical investigations of the SGD phenomenon in Israel. The high resolution time-series ERT measurements using 112-m long cable carried out at the site in 2006 have provided important information regarding shallow coastal hydrogeology up to the maximum exploration depth of approximately 20 m (Swarzenski et al, 2006). In a recent experiment (summer 2008), we focused on deeper parts of the site. This goal was achieved by using roughly two times longer shore diagonal and shore perpendicular ERT lines accompanied by onshore TDEM measurements. Such a combination allowed obtaining reliable information regarding the distribution of electrical resistivity up to a maximum depth of approximately 100 m. As a result, an additional high resistivity structure has been detected at a depth of approximately 63 m, which most likely represents the underlying Carmel Cretaceous aquifer saturated with water of lower than seawater salinity. Two saline/freshwater interfaces were detected at depths of approximately 17 m and 49 m. The upper interface between fresh and brackish water was detected by both ERT and TDEM, while the lower fresh/seawater interface was detected by TDEM alone.