An integrated approach for identification of seawater intrusion in coastal region: A case study of northwestern Saudi Arabia

Seawater intrusion of the northwestern Saudi Arabia, has been investigated through integrated geophysical techniques of electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and time-domain electromagnetic (TDEM). These geophysical measurements were conducted along three parallel NW-SE profiles. Then, processed and interpreted with geotechnical data of four boreholes drilled in the studied area. The results indicate the presence of seawater intrusion at shallow depths between 4 and 10 m below the ground level. These results reveal three layers, which are used here to identify the seawater invasion zone in the study area. 1) The topmost layer with moderate resistivity (14-40 Omega.m) and low P-wave velocity (less than 1000 m/s) indicates a man-made fill and extends down to 5 m depth. 2) The second layer with low resistivity (3-14 Omega.m) corresponding to partially saturated fractured sandstone with P-wave velocity varies between 1000 and 2500 m/s. It is 5-m thick, filled with silty sand and gravel, and contains saline water. 3) The third layer with extremely low resistivity (less than 1 Omega.m) and high P-wave velocity (greater than 2500 m/s) and composed of hard, massive, slightly weathered sandstone. This third layer represents an invaded zone that is highly saturated with seawater. These subsurface characteristics were correlated well with the identified lithological variations obtained from the boreholes. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.