Application of Earth Resistivity , Hydrogeochemistry and Isotope Hydrology Methods for Assessment of Groundwater Recharge in Two Drainage Basins in Northeastern United Arab Emirates

This study analyzed the water chemistry and isotope hydrology of Wadi Al Wurrayah and Wadi Al Tawiyean basins and assessed the contribution of their dams to groundwater recharge. For this purpose, 49 surface and groundwater samples were analyzed for stable ( 18 O and 2 H) and the radioisotope ( 3 H). Results of chemical analysis indicate that the groundwater in the study area is predominantly fresh (TDS < 1,000 mg/L), with salinity ranging from 222 mg/L (TW2) to 935 (TW8), and averaging 500 mg/L. The average values of H and O are -4.80‰ and -2.52‰, in Wadi Al Wurrayah, and -3.16‰ and -11.45‰ in Wadi Al Tawiyean groundwater, respectively, suggesting meteoric water origin. The values of H and O in Al Wurrayah and Al Tawiyean reservoirs are -1.83‰ and 2.04‰, and -2.25‰ and -2.85‰, respectively, indicating evaporative enrichment. Stable isotopes mass balance showed that the dam reservoirs contribution to aquifer recharge varies between 22% and 43%. The average tritium ( 3 H) value of 3.6 TU in Al Tawiyean basins means that the groundwater < 50 years old. Results of 2D earth resistivity imaging survey determined the location of water filled fractures and thickness of the unconsolidated materials in the wadis.