Document Type : Research Paper
phd student in Irrigation and drainage engineering, Water engineering department, Faculty of agricultural and natural resources, Imam Khomeini International University, Qazvin, Iran.
Associated professor. Water engineering department, Faculty of agricultural and natural resources, Imam Khomeini International University, Qazvin, Iran.
Increasing groundwater consumption and increasing water table level leads to changes in the hydrodynamic properties of the aquifer especially the parameters of hydraulic conductivity and specific yield. In this study, which was conducted in 2021 using version 10 of GMS software in Qazvin aquifer, the coefficients of hydraulic conductivity and specific yield of Qazvin aquifer in three census periods of 2002, 2009 and 2018 after calibration and validation of the model in two cases steady and unsteady were determined and compared. The root mean square error in the steady state in the three periods under study was 0.86, 0.73 and 0.84 m, respectively, and in the unsteady state was 1.7, 0.93 and 1.06 m, respectively. That shows high accuracy of the model simulation. The average hydraulic conductivity in the aquifer was estimated in the years 2002, 2009 and 2018 respectively 19.13, 16.85 and 14.06 meters per day and the average specific yield was estimated in the aquifer within the mentioned 0.078, 0.071 and 0.064, respectively. The results showed that with time and the occurrence the decrease of groundwater level, the parameters of hydraulic conductivity and specific yield decrease. since 2015 due to the measures taken in the balancing and artificial recharge plan, the slope of hydraulic conductivity has decreased from 0.38 to 0.31. And the slope of special discharge has decreased from 0.00117 to 0.00078. The main reason for this decreasing trend can be the destruction of soil structure and effective reduction of porosity, and indicates the irreversibility of the aquifer to its previous state. Therefore, it is necessary to pay attention to these changes regarding the recharge of aquifers and return water from irrigation systems.