In order to design and construct hydraulic structures, such as dams, there is a need to determine the amount of river discharge. In ungauged watersheds, it is necessary to calculate their inflows through hydrological simulation. SWAT is one of the numerical models that is widely used for such purposes. For calculating the basin discharge, the model requires meteorological data, such as precipitation, temperature, wind speed, solar radiation and relative humidity, as well as physiographic data related to the basin surface, such as curve number and roughness coefficient.
In this research, the Kasillian watershed in Iran has been used for hydrological simulation based on the SWAT model and the river discharge has been verified using data from Valikben hydrometric station, located at the basin outlet. Furthermore, the impact of each input data on the calculation of water flow has also been examined. Specifically, with an increase of 13.43 percent in the curve number and 0.15 in the overland roughness coefficient of the basin the simulated value of the average monthly discharge 2.52 and 0.01 percent closer to the observed average discharge value. Using all the meteorological parameters, the average mean discharge of the period increased with an error of 14.32 percent.
Keywords: SWAT, river discharge, curve number, roughness coefficient, meteorological parameters.