SWAT model Assessment to determine determination of water balance components of Gamasiab basin

For planning and implementing water-related projects, applying new models and methods is necessary to determine water balance components in basins. Therefore, in this research daily runoff of the Gamasiab basin in the south of Hamadan and Kermanshah provinces was simulated based on cellular network using the spatially semi-distributed SWAT hydrological model in a GIS environment. Digital maps of elevation (DEM), land use, and soil texture and continuous time series of temperature, precipitation, evapotranspiration and discharge were the main model inputs. The model simulates all water balance components in each hydrologic response unit (HRU) and sub-basin using rainfall, temperature and evaporation data. Calibration of model parameters was done for the last 20 years of the studied period (1990-2009) and validation of the model was performed for the first 5 years (1984 to 1989). Based on the results of the simulation, 28% of the area’s total rainfall is discharged from the basin as runoff which nearly matches the data observed at the hydrometric outlet station. Subsequently, to evaluate the model’s performance, simulated values of precipitation, evaporation and discharge were compared with observed data. There was a good agreement between observed and simulated data based on the Nash-Sutcliffe efficiency index (0.6). Hence, it can be concluded that, this model is able to simulate surface and subsurface runoff, deep infiltration and evapotranspiration in the Gamasiab basin.