Catastrophic floods cause losses to millions of lives and property damages every year. The situation is more precarious particularly in countries lacking advanced tools and early warning systems for quick disaster management and mitigation. This article presents a study conducted to develop and understand methodology for delineation of flood extent and identification of various flood risk zones in Prayagraj, India at the confluence of River Ganga and Yamuna (sangam). In this study, a well-established hydraulic model (HEC-RAS 5.0.7 (2D)) and Global Flood Monitoring System (GFMS) tools were utilized. The methodology solves two glitches related to flood studies, i.e., capability of HEC-RAS 2D flood model and GFMS discharge for 1D and 2D flood modeling and secondly using the output of the model, development of a methodology for the identification of various flood risk zones. The modeled and observed data were in close agreement indicating a successful application of HEC-RAS and GFSM data/tools. Using the methodology of this study, various flood modeling and delineation of risk zones can be made for various flood-affected areas in India and worldwide. These tools can also be used for making guidelines for emergency response in flood-affected areas.