Investigating the effect of water level fluctuations in Lenjanat aquifer on Zayandrood river discharge

Numerical simulation of groundwater flow is an important tool for managing aquifers. In this research, the results of a mathematical model simulating groundwater flow in the aquifer of Lenjanat plain located in Isfahan province were investigated. The numerical code MODFLOW-2000, which is in the form of groundwater modeling software (GMS), was used. After collecting the required information (geological, hydrological, hydrogeological and topographic maps), first a three-dimensional hydrogeological model of the plain was prepared using log wells and elevation information of the surface layer of the plain, and then MODFLOW for similar Flow construction was used. After the initial flow simulation, the model was calibrated using trial and error and parameter estimation method and water level information of wells in the region for stable and unstable state. The results of steady-state model calibration for 1995 Square root mean values of mean error, mean absolute error and mean error were 17.41, 15.22 and -0.6 m, respectively, The years 1995 to 2012 were done by trial and error method to achieve the best result between the observed daily balance and the calculated balance. The square root values of mean error and mean error with values equal to 26.29 and 8.43 m, respectively, indicate the relatively good accuracy of the model. After calibration, the amount of feed was 0.300321 m per day, which is 1.98 times the amount of input feed for the model. The amount of horizontal hydraulic conductivity of sand, silt and sand, sand layers was 28.57 and 40.4 meters per day, respectively. The results of fluctuations in river discharge and water level of wells in the region show that changes in groundwater level affect the discharge of Zayandehrud River. Groundwater level forecasts for the next 15 years show that groundwater levels in the region are declining sharply.