The study explores the application of HEC-RAS® for flood routing to estimate outflow hydrographs at bridge sites and culvert entrances, critical for designing and protecting these hydraulic structures from flood damage. Accurate flood level estimation and corresponding afflux near structures are essential for deciding appropriate level of soffit of bridges. While HEC-HMS® is generally employed for flood routing, this study investigates the feasibility and possibility of using HEC-RAS® for unsteady flow analysis. Six models with varying cross-section spacings were developed and analyzed. Comparisons between HEC-RAS® simulations and the Muskingum method showed a strong correlation, with minimal variation in hydrographs across all models. The findings indicate that a maximum cross-section spacing of 4000 m yields optimal outcomes over a 40 km reach. HEC-RAS® effectively simulates flood events, demonstrating its potential as a reliable tool for hydraulic modeling. The study underscores HEC-RAS® capability in generating accurate outflow hydrographs, thus supporting informed design decisions for flood-prone structures like bridges.