Defunct Nile Branches Inferred from a Geoelectric Resistivity Survey on Samannud area, Nile Delta, Egypt

The main objective of this study is to delineate the buried Nile channels and the old settlement areas in the Samannud area of the Nile Delta using geoelectric resistivity surveys. For this purpose, 133 vertical electric soundings (VES) were conducted, using the Schlumberger configuration, along 13 profiles aligned mainly along a northwest direction, i.e. perpendicular to the expected buried Nile channels. In addition, 10 VES stations were obtained close to boreholes for calibration with the lithological and hydrochemical data. These calibrations control the interpretation of the geoelectric resistivity data that are then presented in the form of cross sections and maps. The geoelectric cross sections indicate a topmost layer attaining resistivities ranging from 2·5 to 10ohm.m and thickness from 0·5 to 3m. This layer is correlated with the agricultural layer that is mainly affected by the irrigation and agricultural practices. The second resistivity layer is relatively thick and shows low resistivities ranging from 1·8 to 9ohm.m which is correlated with the clay and silt layer that forms the subsoil water zone. These two layers belong to the Holocene Bilqas Formation. The third geoelectric resistivity layer is characterized by its high resistivity, ranging from 10 to 220ohm.m, which is correlated with the Pleistocene sand of Mit Ghamr Formation. It was found that the surface of this layer is irregular with localized highs and lows. Taking into consideration that the Holocene Nile branches flowed in the low topographic passages on the surface of the Pleistocene sand, while the high topographic areas were inhibited by the ancient Egyptians; the courses of buried channels and sand geziras (settlement areas) are delineated and traced. Referring to the hieroglyphic inscriptions as well as the interpretation and records of historians and geographers, the traced Nile branches are mostly parts of the Bucolic and the Sebennytic branches. Some local high resistivity lenses at different depths are interpreted as sandy point bars within the low resistivity clay. These sandy point bars indicate the locations of stages of the defunct channels that migrated vertically as well as laterally.