Abstract
Parameters as interception, infiltration, water storage on surface holes and soil profile, evapotranspiration are factors of loss water in a watershed and avoid from changing of precipitation to runoff. In this study, by use of HEC-HMS model and comparison of results of different methods of precipitation loss evaluation (Initial and constant, Green & Ampt, SCS curve number, Deficit & Constant and Exponential loss) consider to various purpose function percent error in peak tried to classify the methods. In this way, based on every purpose function, the method with least percent difference of observed discharge to calculated discharge take place in first preference and other methods take place in next preferences. Result show that, Exponential loss method placed in first preference and it selected as optimum method for simulation of runoff and Green & Ampt, Initial and constant, SCS curve number, Deficit & Constant methods placed in next preferences respectively.
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