Simulation and Determination of Hydrological Balance Components in The Upstream of Gheshlagh Dam Using SWAT Model

The aim of this study was to simulate the runoff in the upstream of Chehlgezi hydrometery station in the Gheshlagh Dam watershed, Kurdistan province using SWAT hydrological model. In addition, the results have been evaluated using selected efficiency criteria in the calibration and validation stages, then the performance of the SWAT model is evaluated in simulating the monthly runoff in upland of Gheshlagh Dam. The input model parameters were optimized using the SWAT-CUP optimizer. The calibration and validation of the model was done using SUFI-2 algorithm during 1989-2016 and 2016-2018 periods, respectively. The sensitivity analysis shows that the SCS runoff curve number, Manning’s "n" value for overland flow, minimum and maximum yearly rate of snowmelt, minimum water depth in the shallow aquifer for "revap" were sensitive parameters in flow simulation. The Nash-Sutcliffe and R2 values were 0.62 and 0.65 in the calibration stage, and 0.61 and 0.68 in validation stage, respectively. The results proved the efficiency of the SWAT in monthly flow simulating. According to the results, 55% of the total rainfall entering the watershed has been converted to evapotranspiration, 30% infiltrated into soil and stored as soil moisture, and 15% converted into surface flow component. The results provide useful information on watershed water balance. Flow simulation in different climatic conditions and land-use scenarios in the future can help to sound water resources management.