The extreme rainfall events occurring in recent years have been causing severe damage to social infrastructure and lifeline networks. To address these complex challenges, it is essential to conduct detailed and quantitative analysis of both the extent and causes of damage. This paper examines a specific case in which the Misasa River Bridge collapsed during flooding. Using computational fluid dynamics (CFD) methods, we evaluated the hydrodynamic loads and maximum flow velocities under extreme flood conditions. These hydrological parameters were then compared with values calculated through numerical simulations. Furthermore, we estimated the flood-induced forces acting on the bridge girders and clarified the mechanisms behind the pier collapse.
