Evaluating a Continuous Hydrological Model's Ability to Simulate Peak Flows with Short Time Step (Case Study: Zoshk Basin-Mashhad)

Study on natural processes related to water as well as knowledge about runoff and hydrological conditions is necessary for improvement of water management in Iran. Since most of watersheds in Iran are ungauged, so using hydrologic models to simulate the runoff is inevitable. In this study, continuous distributed hydrologic model WetSpa was used to simulate Zoshk watershed runoff. Three basic maps including digital elevation model (DEM), landuse and soil texture are the model inputs. Required meteorological data are potential evapotranspiration, precipitation and temperature. The basin outlet discharge in Zoahk gauging station is used to calibrate and evaluate the model. Calibration period is from 2009/01/01 to 2011/31/12 and validation period is from 2012/01/01 to 2014/31/12. PEST software was used to calibrate the model parameter. Results show good agreement between calculated and measured hydrographs. The model predicts the hourly hydrographs with a good accuracy, so that according to the Nash-Sutcliff criterion the accuracy is more than 85% and 83% for calibration and validation periods, respectively. The result shows that this model only simulates the high flows well and the simulation result is not appropriate for low flows. This is due to the use of river flow for dry season irrigation.