Studying the Effects of Gavoshan Dam's Irrigation and Drainage Network on Groundwater of Miandarband Plain Using GMS 6.5 Model

Studying the effects of irrigation and drainage network on water table fluctuations is one of the important issues for management of ground water resources. In this study, the effects of establishing Gavoshan dam's irrigation and drainage network on groundwater of Miandarband plain was investigated using conceptual, mathematical model GMS 6.5. The first step to simulate this flood plain is investigating Miandarband's climatological, geological, hydrological and hydrogeological parameters. Using the logs of observation wells, the stratification of layers was identified. The model was run under unsteady flow and calibrated by comparing the simulated water table depth with the depths measured in the piezometric wells for the time interval between May, 2005 and March, 2006. The model validation by using data of hydraulic head of March, 2008 showed an R² of 0.997.  The model was used for exploitation time of irrigation and drainage network. After calibration and evaluation of the model, the effect of exploitation of the Gavoshan dam’s irrigation and drainage network on Miandarband groundwater 1, 5, and 10 years after operation was found to be 1.8, 3.2, and 5.2 m rise in water table. Also, one year after the network operation, 6.59% of the lands would be waterlogged, while this area increases to 37.9% and 56.28% in five and 10 years after operation of the network.