Numerical simulating of Sabzevar Roudab aquifer and checking of influences of constructing Sabzevar Roudab dam on it

Abstract
Background and objectives: Using computer models as a cheap, fast and at the same time accurate method in studying and simulating the flow in a porous media has attracted the attention of many researchers and experts. The aim of this research is to investigate the effects of constructing Roudab dam on Sabzevar Roudab aquifer, which is located dam downstream.
Materials and methods: Sabzevar Roudab catchment basin, with an area about 1828 km2, is located in northeast of Iran in west of Khorasan Razavi province. To manage the surface waters and to supply part of water demand in Roudab plain area, a dam is under constructing on Roudab's river. In order to study the water flow system of Roudab plain aquifer groundwater in Sabzevar and the effect of constructing Roudab dam on it, groundwater model of Sabzevar Roudab aquifer has been simulated using MODFLOW code in GMS software with conditions of existing and not existing of Roudab dam. The aquifer model in steady state condition has been calibrated for the year of 2010 and in unsteady state condition has been verified for 12 month period in year 2011.
Results: The hydraulic conductivity from the calibration of aquifer model in steady state condition is between 4 to 14.7 meter per day and specific yield changes in unsteady state condition calibration is optimal and has been estimated to be between 0.06 to 0.22. The aquifer model studied here has the most sensitivity to the hydraulic conductivity and to the discharge of the extraction wells. The reason is that the major portion of the aquifer depletion is done by the extraction wells and natural discharge has a smaller share in the aquifer depletion. Due to the excessive exploitation of Sabzevar Rudab aquifer, water table has dropped in this plain. The severity of the decline in several areas depends on the amount of recharge and discharge of an aquifer. In other words, the general trend of the plain hydrograph is descending and its water balance is negative.
Conclusion: The model results show that the water table curves presented by the aquifer model, before and after constructing the Roudab dam do not show any significant changes, because the groundwater water balance before and after constructing the dam is not significantly different and also because it is almost unaffected by the surface recharge. It is worth mentioning that constructing Sabzevar Rudab dam would lead to further decline of the water table elevation of the aquifer. Has been predicted average decline of the water table in Roudab aquifer in years of 2014, 2015 and 2016 will increase about 0.17, 0.2 and 0.23 meters, respectively.
Keywords: Sabzevar Roudab aquifer, Groundwater Simulation, GMS.