To estimate the Rainfall-Runoff process popularly used watershed model is Hydrologic Engineering Centers–Hydrologic Modeling System (HEC-HMS), which is generally used to estimate the basin's hydrological phenomenon caused due to precipitation. It helps to predict the various hydrologic responses to watershed management and to have the best understanding of the effect of these practices. It is specific from the spacious study of the literature that the studies on relative assessment for hydrologic simulations are finite in developing countries including India. This case study dealt with hydrological modeling software of HEC-HMS is used to simulate the Rainfall-Runoff process to derive hydrograph at the outlet of 'Karcham' catchment, Himachal Pradesh, India. In this study, the SCS curve number method is applied to determine the loss model as a major component in Rainfall-Runoff modeling. To enumerate runoff volume, peak runoff rate, and flow routing methods SCS-Curve Number, SCS-Unit Hydrograph, and Muskingum routing methods are chosen respectively. The simulated peak flood hydrograph obtained with open source spatial and meteorological data at the outlet of 'karcham' watershed was 5663.6 m3/s. The predicted discharge is lesser than 1.4% of the simulated discharge. The results of the present study indicate that HEC-HMS is a tool applied to derive flood hydrographs with open source spatial and non-spatial data in absence of virtual data to achieve the various objectives.