Simulation and perdiction nitrate in ground water (Case study: south khorasan-Birjand aquifer)

Groundwater is one of the main sources of drinking water supply, agriculture, and ... in Birjand region , So the management of underground water table is very important. GMS software is one of the most prestigious models based on groundwater modeling that considered with steady and unsteady flow. This model is able to simulate and predict the future status of an aquifer with defined scenarios. The purpose of building a conceptual model is to simplify the field problem and organize the associated field data so that the system can be analyzed more readily. For Steady state September .month was selected that have less oscillation in water table, and for un-steady state October 80 to August 91 during 20 time steps were selected. After running the model, calibration and sensitivity analysis according to the underground water balance perform, and show that model is sensitive toward hydraulic conductivity and in unsteady state is sensitive toward specific yield. Based on balance equation the aquifer will have 10 meters shortage in water table in aquifer in 5 years prediction. In this model for predict quality in birjand plain used MT3D modules. In the model due to lack of quality parameters, in MT3D only Nitrate (No3) was investigated and the results indicate the correlation between water table and increasing in nitrate. During 5 years increase nitrate in lowering of birjand city and agriculture land.