Currently, the extraction of water resources, especially groundwater, has significantly increased. This is because in most arid regions, despite the scarcity of surface water resources, all the pressure to supply water comes to these valuable resources. However, in many cases, this pressure exceeds the capacity of aquifers, leading to a decline in groundwater levels and events such as subsidence in aquifers. Iran is also considered a dry and semi-dry region, and its aquifers do not experience favorable conditions. In recent years, Iranian aquifers have frequently experienced a decline in groundwater levels. The important point is that some aquifers have not only not experienced atmospheric drought, but they are suffering from a drop in the groundwater level despite the atmospheric wet. This decline in groundwater levels is solely a result of human-induced over-extraction. Therefore, to prevent successive declines and improve the aquifer's situation, water resource management must be prioritized, and effective and timely decisions need to be made. Since implementing management decisions for aquifer revival requires significant costs and a long time, the use of numerical models for aquifer simulation and eva‎luating these decisions in this model can be much quicker and cost-effective. However, to simulate an aquifer, a comprehensive study from all aspects is required for the simulation to be close to reality. This study focuses on simulating the Lenjanat aquifer located in the Gavkhoni basin. The large area, the presence of major industries like iron and steel melting, and the passage of the Zayandehrud River through the Lenjanat area have increased the importance of the Lenjanat aquifer. The Zayandehrud River, due to creating exchange with groundwater, poses a significant challenge in this simulation. The simulation of this aquifer was performed using the GMS software with the MODFLOW numerical code. The simulation was conducted in both steady-state and transient conditions. An aquifer simulation is valid when it can accurately simulate various time periods of the aquifer, resembling reality. Therefore, the aquifer modeling for the Lenjanat aquifer was done in a steady-state for octobr 2010 and in a transient state for the period from September 2017 to october 2019. After the final calibration, the model's accuracy was validated for the period from october 2018 to September 2020 . The computed and observed groundwater levels i october 2010 are 1779.93 meters and 1779.89 meters, respectively, confirming the close resemblance of the simulation to reality. The modeling error, based on the Root Mean Square Error (RMSE), decreased to 50 centimeters in the steady-state condition. In the transient condition and validation, the error was 1.83 meters and 2.57 meters, respectively. The error rate, based on the Mean Absolute Error (MAE), was 0.39 meters, 1.47 meters, and 2.07 meters in the steady-state, transient state, and validation, respectively. After confirming the model's credibility, it can be relied upon, and by applying management policies to the model and examining the results for improving the aquifer's situation, timely decisions can be made. Five management policies were introduced to the model as scenarios, with the consideration of socioeconomic aspects. The best scenario suggested an average increase of 3.3 meters in computed groundwater levels by reducing the average consumption simultaneously and proposing a 20-centimeter increase in river ater head with a 10% reduction in consumption. Under this scenario, the groundwater level in the last step becomes very close to the groundwater level to october 2010. In fact, this suggestion can practically revive the aquifer in the coming years..

حميدرضا صفوي

محمد رضا نيكو

محمدحسين گل محمدي , رامتين معيني