Evaluating Three Conventional Electrode Arrays in 2d Electrical Resistivity Imaging Surveys for Studying the Sedimentary Layers and the Hydrogeological Situation in Southern Iraq

Abstract

This study compares three conventional electrode arrays in 2D electrical resistivity imaging surveys by applying them to study the sedimentary layers and the hydrological situation in three coastal locations close to the Khor Al-Zubair, southern Iraq. At each location, a 2D imaging line of 1200 m length wasimplemented columnar the Khor Channel, using Dipole-dipole, Wenner and Wenner-Schlumberger arrays at the same line. The inverse models revealed the presence of three major resistivity layers, the uppermost layer has a medium resistivity attributed to the upper aquifer and is affected by the salinegroundwater. The second electrical layer represents the upper aquifer, completely filled with brackish groundwater. The third, very low resistivity layer correlates to the lower aquifer and is filled with saline groundwater. Also, a hard clay bed (aquiclude) is visible on all geophysical lines in the depth range of 20 m-28m. Results indicate that all three electrode arrays can detect the sedimentary layers and the extension of saline groundwater but with a difference in accuracy. The Wenner-Schlumberger array revealed the best results in delineating the resistivity layers, the extension of saline groundwater in the uppermost layer of aquifer and the clayey aquiclude and shows the best horizontal and vertical resolutions. The dipole-dipole array was less accurate in determining this extension of saline groundwater and the aquiclude. The Wenner array results were unsatisfactory in delineating the aquiclude and the lower aquifer. The Wenner-Schlumberger array, as hypothesized, is efficient in determining different resistivity layers, especially in the presence of horizontal and vertical structures or high background noise, and if long survey lines are required.