THE USE OF SEISMIC REFRACTION AND ELECTRICAL TECHNIQUES TO INVESTIGATE GROUNDWATER AQUIFER, WADI AL-AIN, UNITED ARAB EMIRATES (UAE) By Amir Gabr, Ahmed Murad, Haydar Baker, Khalid Bloushi, Hasan Arman, & Saber Mahmoud Geology Department, Faculty of Science, UAEU Al-Ain, UAE Amir.Gabr@uaeu.ac.ae Abstract—Twenty seismic refraction profiles, three Vertical Electrical Soundings (VES) and Three Electrical Resistivity Tomograms (ERT), using Wenner Array were acquired along Wadi Al-Ain, in order to study the aquifer's geometry, groundwater level and locate the promising sites for future drilling. The seismic velocities distribution analysis indicated that, there are three different zones ranging between (590 – <1400 m/s), (1400 – <1800 m/s) and (1800 – 5300 m/s). The obtained results show that the first low velocity values may indicate the unsaturated zone which is directly affected by the surface water that appears along the studied area. The second velocity range may reflect the water level at the saturated zone or the main aquifer. The third range of velocity reflects the lithological interfaces. The estimated depth to the unsaturated zone varies between 2 m to 7m. The depth to the saturated zone ranges between 10 m and 15 m. However, the lithological interfaces depths is detected clearly at 15 m to 25 m. This represents the gradual increase of seismic velocity layers with depth. This increase may be due to the dense formation which change vertically from alluvial to compacted sediments and then to limestone. The integrated seismic refraction profiles, VES and ERT results show that the aquifer is a Quaternary alluvial deposits aquifer, which consists mainly of gravels, sand and clay with average thickness of about 15 m or more and underlained by compacted sediments and limestone. The apparent resistivity of the aquifer shows a surficial resistive layer of dry alluvium with resistivity of 700 .m then lower resistivities reach to 5 .m, then increasing gradually with depth to about 566 .m or more through 100 m thickness. ERT profiles also confirm the water depths, obtained from seismic refraction analysis. This integration confirms the existence of a fresh groundwater within this interval. The obtained results show that any future drilling for groundwater, a number of the VES positions may be considered as potential locations. Keywords: Seismic Refraction, VES, ERT, Groundwater, Aquifer, Al- Ain 1. INTRODUCTION The study area is situated in Al-Ain in the eastern part of Abu Dhabi, United Arab Emirates (UAE), near the border with the Sultanate of Oman and at the western margin of the Northern Oman Mountains (Ellison et. al., 2006) (Figure 1). Although Al-Ain is located within the arid desert belt of the world and characterized by drainage net formed as a result of the prevalence of humid climate during the Quaternary, it is one of the largest and ancient oases of the Arabian Peninsula due to the fresh groundwater supply which is derived from the Oman Mountains to the East (Hunting, 1979). The seismic refraction method is an important geophysical method. It has been adopted to investigate the groundwater level in the study area, which has recently become very shallow in some part of Al-Ain. The objective of the seismic survey measurements is to confirm or not the assumption that the groundwater level can primarily be revealed by seismic refraction technique especially in the gravely-sands or silty clay areas, in which the groundwater level can be determined as a boundary of acoustic impedance (Galfi & Palos, 1970). Shallow seismic survey can be useful to be integrated with the Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT), in order to investigate changes in the groundwater level and to possibly locate the groundwater aquifer and promising sites for future drilling.