Original Article

Environmental Geology

, Volume 46, Issue 6, pp 741-749

First online:

Use of chloride-mass balance and environmental isotopes for evaluation of groundwater recharge in the alluvial aquifer, Wadi Tharad, western Saudi Arabia

  • Ali M. SubyaniAffiliated withHydrogeology Department, Faculty of Earth Sciences, King Abdulaziz University Email author 

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Groundwater recharge estimation has become a priority issue for humid and arid regions, especially in regions like Saudi Arabia, where the precipitation varies over space and time as a result of topography and seasonality. Wadi Tharad is a typical arid area in western Saudi Arabia. Within its drainage area of 400 km2, the groundwater system shows a graded hydrochemical zonation from the hydrocarbonate in the upper reach to the chloride zone in the lower reach. The saturation index (SI) varies depending on the concentrations of carbonate minerals; the mean for calcite and dolomite is about in equilibrium (e.g., zero value). As halite and gypsum indices are negative, it is undersaturated. Isotopic compositions of H and O in the groundwater show that the groundwater recharge resources are mainly from meteoric water. The chloride-mass balance method was refined to estimate the amount of recharge, which is probably 11% of the effective annual rainfall. These results can be used to improve the accuracy of future groundwater management and development schemes.


Stable isotopes Recharge Saturation index Arid regions Saudi Arabia