Estimating recharge into the Semnan alluvial aquifer using saturated zone studies

The assessment of recharge is one of the most important issues in management and planning of the groundwater resources. In this study, the amount of recharge to the Semnan alluvial aquifer was investigated using methods of water table fluctuations (WTF), chloride mass balance (CMB), water budget and stable isotopes. The parameter is highly important for managing this vital aquifer as over-exploitations for drinking, agricultural and industrial uses occurred, resulting in water table decline with an average rate of about 80 cm annually. Based on the results, the values of recharge into the Semnan alluvial aquifer are estimated about 4.4, 2.5 and 2.1 MCM/year by WTF, CMB and water budget methods, respectively. The isotopic data (18O and 2H) do not show any significant effects of evaporation on recharge process, confirming the main role of highland recharge in this arid-land aquifer. Combining results of the recharge studies in saturated zone of Semnan aquifer, yields annual rainfall recharge of about 3 MCM, which is about 5% of the annual precipitations.