hydrological impacts of large reservoir dam and land subsidence on downstream groundwater resources using mathematical modeling

Spatial and temporal change of groundwater recharge is crucial for effective groundwater resources management especially in arid and semiarid regions. human activities such as reservoir construction commonly interrupt the balance of the subsurface system. the main aim of this study was to investigate the interaction impacts of land subsidence and dam construction on mosian aquifer located at the northwest of iran. groundwater mathematical model (modflow), geographic information system (gis), and stochastic weather generator model (lars wg) were used for predict the impact of dam construction on groundwater balance of the study area. according to results, from 1991 to 2014, groundwater level declination and land subsidence at the downstream area of the dam were 11.22 and 0.45 meter respectively. constructed dam has different effects on some components of water balance. river recharge decrease by 65 percent, whereas, recharge through return water increase by 50 percent. the results of the prediction indicate that groundwater level will decrease continually, as the annual groundwater declination will be 0.58m for the period of 2015 to 2030.the results also show that dam construction should decrease the trend of the groundwater declination. predicted average of groundwater declination was 0.58 and 0.65 m when simulation was implemented for dam and no dam condition respectively. the effect of land subsidence on groundwater declination was not noticeable compared to effects of the groundwater discharge.