Although dams are beneficial for irrigation and power generation, they can also change the course of rivers and raise the possibility of flooding in downstream areas. Multiple hydropower dams have been constructed on rivers upstream that flow into the alluvial plains of Assam, renowned for their unpredictability and frequent flooding. This study employs an advanced hydrodynamic modeling framework to generate the flood inundation scenarios that would occur because of different dam flow releases downstream of Ranganadi dam (erstwhile Panyor hydropower dam) at village level. For flood inundation simulation, the HEC-RAS model that geometrically imports the high-resolution DEM, land use and land cover layer, and the long embankment shape files available on both sides of the river was used to accurately represent the high-ground floodplain of the study area. The structured mesh of 15 m × 15 m was generated as 2D flow perimeters, and a refined mesh of 5 m × 5 m was drawn to regenerate a much finer computational mesh along the main channel and the floodplains. Two sets of input boundary conditions, i.e., the observed flow hydrograph ranging from 240 to 760 m3/s and the hypothetical flow hydrograph ranging from 700 to 1200 m3/s and the constant normal depth, were used as the output boundary for the study, analogous to a friction slope based on the land slope in the vicinity of the 2D flow area boundary condition line. To maintain the stability and output accuracy of the model, a computation time step of 1 s was set up for the study. The simulation revealed that the flood inundation extent and depths, because of the observed 640 m3/s peak flow and its prolonged duration of 50 h are greater than the inundation caused by the observed 760 m3/s peak flow with a shorter duration of 15.16 h, as seen in the case of the Dolabhanga Village, which is fully inundated with the previous flow rather than the latter. The hypothetical scenarios were generated by gradually increasing the flow discharge for the same duration. This study will help decision-makers better understand flood dynamics, including flood inundation mapping, hazard assessment, and adaptation measures to identify flood-prone locations, rank mitigating strategies, and create emergency response plans.