effect of irrigation efficiency increasing on groundwater level fluctuations (cast study: ajab-shir plain, east azarbaijan)

excessive withdrawal of groundwater and reduced rainfall in recent years have caused the drawdown of groundwater table. therefore, it is necessary to manage it for preventing its damage. the present study was carried out to investigate the effect of increasing the irrigation efficiency on groundwater fluctuation on ajab-shir plain aquifer. the aquifer was simulated by using visual modflow 3.1 software. the steady state calibration of the model was carried out by using data from october 2004. then the model was calibrated for unsteady state condition by using data from october 1999 to september 2005. finally, the groundwater level and water balance of the aquifer were forecasted in two states: continuing the present irrigation method (surface irrigation) and changing it to pressurized irrigation system for fall 2005 to summer 2021 period. based on the results, with the current irrigation conditions, the aquifer water balance will be equal to -2.43 m3/year for the end of the prediction period. by increasing irrigation efficiency, the balance value was forecasted to be 3.99 m3/year (3.23 m3/day increase). also, the results showed that changing irrigation systems will lead to an average increase of 4.63 m in the groundwater level of ajab-shir plain at the end of the prediction period.