Coupling of WetSpass-M and MODFLOW Models for Groundwater Flow Assessment 

Abstract Recharge is considered a key parameter in groundwater models for sustainable management of aquifers, which is influenced by factors such as land use, soil, weather, etc. The present study was conducted to couple WetSpass-M and MODFLOW models for evaluating Neyshabour aquifer condition in steady and transient states. To this aim, the simulated recharge by the WetSpass-M model was applied as an input of MODFLOW to assess the groundwater balance. The hydrodynamic coefficients were determined by calibrating the model, evaluating and the model sensitivity to the hydraulic conductivity coefficient, specific yield (Sy), and recharge. The results indicated that the annual average of surface runoff, actual evapotranspiration, interception, and recharge during 1991–2017 equaled 18, 36, 7.6, and 42.6% of the average annual precipitation in the basin, respectively, with the simulated water balance error 4.2%. The average annual recharge of the basin varies between 0-257.41 mm with an average of 105.25 mm/y. Accordingly, the maximum and minimum average monthly recharge occurs during March and July, respectively. The appropriate matching of the simulated and observed water levels and obtaining the suitable values of RMSE, R2, ME, and MAE evaluation criteria in steady and transient states indicate the adequate accuracy of the WetSpass-M model in estimating the recharge and success of the couple two models. Based on the simulated groundwater balance, the aquifer faces a deficit of 421.3 MCM per year and 97.41 cm in the annual groundwater level. The model displayed more sensitivity to the hydraulic conductivity coefficient compared to other parameters.