Delineation of saline groundwater and sea water intrusion zones using transient electromagnetic (TEM) method, Wadi Thuwal area, Saudi Arabia

Abstract

In the coastal western part of Saudi Arabia at Thuwal area located close from the Red Sea, the shallow groundwater specific electrical conductivities measured at the drill holes range from 6 to 13 mS/cm. In order to study the origin of this salinity, a good knowledge is required of the aquifer geometry with depth. Ninety nine transient electromagnetic (TEM) soundings were carried out over an area of about 100 km 2 . From the TEM profiles, a conductive substratum with a resistivity of 1-13 Ωm was identified at most of the sites at depth ranging from 50 to 150 m. This substratum is related to Oligocene-Miocene sediments (Shumaysi Formation) which are mainly red clay-rich formation containing brines at coastal zones. Clayey sediments are more likely present in the southeastern part and along the faults that run NE-SW across the study area and parallel to the Quaternary volcanic which runs NW-SE. The study demonstrated the effectiveness of the TEM sounding method to map conductive zones.

Application of time-domain electromagnetic method in mapping saltwater intrusion of a coastal alluvial aquifer, North Oman

“…The ability to acquire vertical and lateral data without drilling makes the TDEM technique quite cost effective, as a non-destructive and non-invasive method, especially in the reconnaissance mapping of the lateral extent of salt-water intrusion, estimating its approximate depth and any changes within the saltwater transition zone (McNeill, 1990;Shah et al, 2007). TDEM soundings are particularly well-suited to delineate the layered structures of interest in geologic, as well as groundwater exploration and for mapping the boundaries between fresh-water and salt-water in coastal aquifers, because of its ability to detect good conductors, such as clay and shale, as well as saline water environment (Kontar and Ozorovich, 2006;Al-Garni and El-Kaliouby, 2011;Rajab and El-Naqa, 2013). TDEM method is particularly effective in areas with dry surface and it can explore the ground at depths ranging between a few meters to several hundred meters, whereas other geophysical methods such as DC resistivity fails due to the high contact resistance between the electrodes and surface layer and long array to achieve the desired depth (McNeill, 1990).…”

“…Eddy currents induced by the time-varying magnetic field generate, in turn, secondary magnetic field in the electrically conductive earth. The amplitude and rate of decay of these secondary fields are measured at the surface and analyzed in terms of the variation in electrical resistivity with depth (McNeill, 1994;Shah et al, 2007;Al-Garni and El-Kaliouby, 2011).…”

“…Kontar and Ozorovich, 2006;Al-Garni and El-Kaliouby, 2011). The characteristics of the TDEM responses of the earth to a pulsed primary signal from a large wire loop laid on the ground surface yield information about the variations of the electrical resistivity with depth.…”

Seismicity and seismotectonics of the Jeddah area, Saudi Arabia

“…This earthquake activity can be taken as indicator for tectonic activity of some recorded fault trends through this zone. The previous geological and geophysical investigations have confirmed the presence of major NE-SW and NNE-SSW fault trends through Wadi Thuwal area (Al-Garni et al [3]; Al-Garni and El-Kaliouby [2]). In addition, evidences of shear zones are observed close to Harrat Thuwal (Al-Garni and Gobashy 2009).…”

“…Depending on the distribution of earthquakes, fault parameters (strike and dip) of the major structural trend, seismicity parameters (a-and b-values, Table 1) and previous geological and geophysical studies (Alwash and Zakir [4]; Al-Qarni [5]; Al-Garni et al [3]; Al-Garni and El-Kaliouby [2]), five seismogenic source zones have been identified (Fig. 7).…”