Performance Evaluation of SWAT Model to estimate surface runoff in Kachik Watershed, Golestan Province

The ability of a watershed model to predict the channel flow, appropriately, for particular applications will be assessed by calibration, validation and sensitivity analysis. In this study SWAT model was applied to simulate runoff in the Kachik watershed with an area about 3600 hectares in Golestan province. For doing this purpose, the sensitivity analysis using sensitivity analysis tool SWAT2009 were performed due to availability of this tool in model software. Results showed that threshold height of water in the shallow water table that needs to be done back (GWQMN), curve number (CN2), soil evaporation compensation (ESCO), available water capacity of the soil layer (SOL_AWC), soil hydraulic conductivity at saturation (SOL_K) were most important factors controlling the flow rate in the studied watershed. Secondly, SWAT2009 model performance evaluation through the calibration and validation was performed. Data 2004 was selected as calibration period and 2005 and 2006 were determined as validation period. The results of model evaluation have illustrated that determination coefficient of calibration and validation periods are 0.71 and 0.75 and coefficient of Nash-Sutcklief are 0.70 and 0.71. So we can conclude that the SWAT model can predict surface runoff with high precision.