USE OF SEISMIC REFRACTION, VERTICAL ELECTRICAL SOUNDING AND ELECTRICAL RESISTIVITY TOMOGRAPHY TO INVESTIGATE THE GROUNDWATER AQUIFER, WADI AL-AIN, UNITED ARAB EMIRATES (UAE)

Amir Gabr, Ahmed Murad, Haydar Baker, Khalid Boulshi, Hasan Arman, Saber Mahmoud
Geology Department, Faculty of Science, UAEU, Al-Ain, UAE

Abstract

Groundwater is one of the main Earth resources required to meet the demand of water increase, especially in wadi Al-Ain, UAE. Twenty seismic refraction profiles, three Vertical Electrical Soundings (VES) and three Electrical Resistivity Tomograms (ERT), using Wenner Array were acquired along the study area, 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, 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 wadi. 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 explained to be related to dense formation which change vertically from alluvial to compacted sediments and then to limestone. This change can be observed in the outcrops in the surrounding area. The integrated seismic, 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 or limestone. The apparent resistivity of the aquifer shows a surficial resistive layer of dry alluvium with resistivity of 80 W.m then lower resistivities reach to 15 W.m and then increasing gradually with depth to about 566 W.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 VES positions may be considered as potential locations.