Journal of Watershed Management Research

  Among the variety of method s used for estimating runoff in the watershed, the SCS method has universal applicability, so the main aim of this study is the calibration of SCS method and the creation of flood hydrograph. The HEC-HMS hydrologic (rainfall-runoff) model has been used for Idanak watershed flood estimation. Using the residual sum of squared minimization function”, calibration process was completed and the results were evaluated at the end. The results indicate that models with no use of calibration would not be trustful. Relying on model parameters (CN, I_a) estimation using experimental relationships causes poor match between observed and simulated runoff and proves the necessity of calibration. In the models calibration and validation the difference of peak flows between hydrograph and simulated hydrograph is always less than 10 percent and coefficient of determination between the two is 0.82. the calibration model results show the efficiency of the model in estimation of runoff and flood peak flow. The validation results associated with the volume of runoff is not acceptable, because the difference between observed and simulated runoff volume is more than 31 percent .