Use of Geoelectrical Resistivity to Delineate the Seawater Intrusion in the Northwestern Part of the Nile Delta, Egypt

Mapping of the boundaries between freshwater and saltwater was helpful in surface resistivity surveys because of the high electric conductivity of saltwater relative to freshwater. A total of 30 electrical soundings were measured to configurate the seawater intrusion. Accordingly, two zones of groundwater quality were delineated: the slightly freshwater zone in the southern part, with resistivity range of 15–90 Ω m, and the brackish water to saltwater zone, with a very low resistivity of <2 Ω m in the northwestern parts. In addition to tracing the freshwater-seawater contact zone, three geoelectric layers were detected. The surface layer composed of sand, clay, and silt. Its resistivity ranges from 5 to 512 Ω, and the thickness varies from 1 to 25 m. The aquifer layer is composed of sand with intercalations of clay with resistivity ranging from 15 to 90 Ω m and thickness from 25 to 120 m. The clay layer resistivity ranges from 2 to 15 Ω m and thickness from 2 to 69 m.