Comparison of the Three Different Abstraction Estimation Methods of Rainfall in HEC-HMS Model in Runoff Simulation (Case study: Kermanshah Gharasoo watershed)

Rainfall-runoff modeling is one of the key items that considered in hydrology to achieve flood characteristics. In this study, HEC-HMS model performance was evaluated using the SCS-CN, Green-Ampt and Initial and Constant infiltration methods in predicting runoff volume, peak flow and time to peak, in simulation of rainfall- runoff hydrograph at Gharasoo watershed, located in Kermanshah province. Eight rainfall–runoff events were simulated by HEC-HMS model and compared with the corresponding observations events. Results shown a well accuracy in predicting runoff volume (R2=0.84, E=0.81 and CRM=0.06) was achieved using the SCS-CN method (after calibration). However, Peak flow was better estimated using the Initial and Constant method (R2=0.96, E=0.95 and CRM=0.01). Furthermore, shape of the calibrated hydrographs were very similar to the observations hydrographs for both SCS-CN and Initial and Constant methods. However, adopting the Green-Ampt method, showed low reliability in total runoff volume and peak flow estimating. Model accuracy in estimates of modeled the time to floods peak, were evaluated by comparing observed and simulated values through the selected approaches, so that the results of time to floods peak showed the highest reliability in SCS-CN method (6.36%).