Surface water and groundwater interactions have been always one of the basic parts of the water resources management. Such interactions are usually considered as internal boundary conditions in modeling and the exact state of the elements is determined during the simulation. In this research, modeling of Najafabad aquifer (No. 4206 based on national codes of Water Management Organization) has been studied. Considering the last fronts of Najafabad watershed and aquifer, based on 3 independent sub regions, determination of new fronts of the basin has also been studied. Reviewing geology maps of the basin, meteorological stations data, exploration wells logs, pisometers and pumping wells data, irrigation network information and, with required statistic procedures, conjunctive simulation model of the basin has run. Using satellite images and GIS technique, increasing model capabilities has also been studied. Finally the model has run in both steady and unsteady states, and basic parameters calibrated during the procedure. Final results of calibrated model have been studied in sensitivity analysis. Riverbed thickness which is one of the main factors of conjunctive modeling, determined in average during 36 km reach of passing river (zayandeh-rood). Effects of uncertainty on model results and using probabilistic data, has also studied using stochastic model. Hydraulic head values, mass balance, drawdown and other parameters also calculated in steady and unsteady models. Basic role of Zayandeh-rood river in recharging the groundwater resources of the region computationally confirmed. Hydrodynamic coefficients of the aquifer also determined in selected sub regions. Respectively infiltration factors determined based on model results separately in recharge and discharge zones. Finally, a few suggestions have been considered for future researches in related to the large – scale surface eater and groundwater conjunctive management.
