Application of HEC-HMS for simulation of peak runoff rates from a small watershed

Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS), a versatile hydrological model, was applied to a small watershed situated in Chotanagpur plateau region of India for simulation of peak runoff rates. Initial and constant loss method and Snyder unit hydrograph were chosen for computing the precipitation losses and transforming the estimated runoff into direct surface runoff, respectively. Seven sets of observed hyetographs and corresponding flood hydrographs were used for calibration of model parameters viz., initial loss, constant loss rate, Snyder peaking coefficient and standard time lag. The model output was validated with other set of flood hydrographs (five in number) of the same watershed. A simple linear relationship between predicted and observed peak flow rates was also developed. The HEC-HMS simulated depths of runoff and peak runoff rates matched reasonably well with the observed data. The average value of absolute relative error in estimated peak, a measure of goodness of fit between the peak runoff rates of predicted and observed hydrographs was found to be 6.94%. It was concluded from the study that the HEC-HMS model with the calibrated parameters can be safely used for the determination of the depth of runoff and peak runoff rates from ungauged watersheds with similar hydrological conditions