Daily flow simulation of Chehelchai river- Golestan province using SWAT model

In this study, daily flow of the Chehelchai watershed was simulated using the Soil and Water Assessment Tool (SWAT) model. The main objective of this study was to evaluate the performance of SWAT model and the applicability of this model as a flow simulator at the Chehelchai watershed. In order to have a successful calibration, a process of parameters sensitivity analysis was performed and then calibration and validation of the model were performed using the recorded data of 7 years. The data from 2001 to 2004 was used for calibration and those of 2005 to 2007 for validation. The results of sensitivity analysis showed that soil evaporation compensation factor (esco), curve number (CN), soil available water capacity (sol-awc), deep aquifer percolation fraction (rchrg-dp) and soil bulk density (sol-bd) had the most influence on output of the model. During calibration, the simulated daily flow matched the observed values with a Nash-Sutcliffe coefficient of 0.57 and a coefficient of determination (R2) 0.62. These values were 0.32 and 0.42 during the validation. The results of simulation bases of monthly flow showed beter accuracy and good correspondence.