Investigating the Impact of Vadose Zone on Groundwater Modeling by UZF package of MODFLOW-NWT(Case study: Neishaboor Plain)

This study was conducted to investigate the effect of vadose zone modeling on groundwater recharge, and comparing this method with conventional method of ground water modeling. Hence, Neishaboor plain was selected as a case study. MODFLOW-NWT model was chosen to simulate the flow of saturated zone. The UZF package simulates flow through the vadose zone while the RCH package transfers recharge directly to the saturated zone. Recharge defined for the two groundwater models was obtained from the SWAT model. Automatic calibration of the models was done with PEST form2000 to 2010, and verification of the models was done form2000 to 2010. RMSE of the conventional method (RCH package) and modeling vadose zone (UZF) in calibration stage were 1.45 m and 1.52 m, and in verification stage was 1.80 and 1.62 respectively. Results of UZF indicate recharge enter to the saturated zone with 1 to 56 month lag times in different areas. The sensitivity analysis of models demonstrated that the model, which considered UZF, was moresensitive to input parameters. Findings revealed that taking into account the vadose zone in groundwater modeling, can improve performance of the model, and makes it possible to calculate the lag time and part of infiltration that stored in vadose Zone.