Estimating recharge is important in groundwater studies, especially in budget calculation to properly manage groundwater withdrawals. In this research, recharge value into the alluvial aquifer of Sarakhs, which is the only source of water for drinking, agricultural and
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Estimating recharge is important in groundwater studies, especially in budget calculation to properly manage groundwater withdrawals. In this research, recharge value into the alluvial aquifer of Sarakhs, which is the only source of water for drinking, agricultural and industrial uses in Sarakhs Plain (NE Iran and adjacent to Iran-Turkmenistan border), was estimated using MODFLOW model in FREEWAT Software. After preparing the conceptual model of the aquifer and transforming it into a numerical model, the model was calibrated in unsteady states during a two-year period (water-year 2015-2016 and 2016-2017) and verified. The sensitivity process confirmed validity of the numerical model in estimation of the aquifer recharge. Accordingly, the annual surface recharge was estimated at 80 million cubic meters (Mcm), occurring from rainfall (32 Mcm/year) and irrigation return flows (48 Mcm/year). In this regard, rainfall recharge coefficient was estimated about 20% of the annual rainfall and irrigation return flow coefficient was calculated about 15% of the annual discharge rates of the discharging wells. Simulated temporal variations of the groundwater recharge indicates occurrence of the rainfall recharge during January to June and irrigation return flows from November to April each year. The estimated recharge coefficients can be used in budget studies to properly manage the Sarakhs aquifer, as well as the same aquifers in Iran.
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