واسنجي مدل آبدهي ماهانه براي حوزه‌هاي آبخيز كوچك

Calibration of Monthly Water Yield Model for Small Catchments

For watershed management and water resources planning need to know hydrological relationships among the time series of monthly runoff depth especially at small watersheds. To investigate the ability of selected mathematical model for simulation of monthly runoff depth, 7 catchments were selected in and around of Zanjan province. Areas of all selected catchments are less than 170km2 and acceptable hydrometric data time series long equal 6 to 27 years. At every selected catchments depth of precipitation, runoff and potential evapotranspiration by method of Blaney-Criddle estimated for months of every water year. Sometimes because of shifting partial of winter snow melt runoff to spring season, the monthly hydrometer data was divided to total and sectional data series so that proportion of runoff depth to precipitation depth was less than one certainly. After calibrated the coefficients of mathematical model named (GR2M) by application of all or partial of data series based on maximizing Nash-Sutcliffe coefficient as model performance criterion. Result is that by application of only the partial of data series, Nash-Sutcliffe coefficient is increased 10%. So from viewpoint of geological formations and rock units the sub watersheds divided into two clusters with difference measure of 0.14 about the quantity of outside basin calibration coefficient. Precise of calibrated model of (GR2M) for small and similar climatology condition based on height from sea level and geology conditions evaluated average to good. Key words: Monthly