The Simulation of Stream Daily Flow Using Spatially D istributed Hydrological Model, WetSpa: A Case Study of Arazkoose, Gorganrood Watershed, Golestan Province

In the past decades، much effort has been devoted to simulation of the rainfall-runoff process and a lot of models have been suggested for this purpose. Hydrological models are simplified representations of the natural hydrologic system. The choice of these models depends mainly on the objective of the modeling and also the available information. In this study، the river flow and surface runoff are simulated using the model WetSpa. WetSpa is a continuous، distributed، and physically based hydrologic model that simulates hydrologic processes in pixel size of 1 m2. In this study، meteorological data from Arazkoose watershed -a part of Gorganrood watershed in Golestan Province- during 1989 to1993 consisting rainfall، temperature and evaporation measurements in 3 stations were used as WetSpa input data. To run the model three base maps including DEM، land use and soil type with cell size of 80 m were provided. Simulation results show a relatively good agreement between calculated hydrographs and measurements at the basin outlet. The model estimates daily hydrographs، with accuracy of 62% and 50% based on Nash-Sutcliff criterion، for calibration and validation periods، respectively and the maximum flow rate with accuracy 85%.