Hydrodynamic Effects of Flash Floods Considering the Bridges and Their Blockage in South China

Amidst intensifying climate change, flash floods are becoming more recurrent, posing significant threats to safety and assets, especially in mountainous areas. Given the non-negligible influence of bridges on flash floods, this research capitalized on fluid dynamics simulations to examine the mechanisms by which six bridges within the investigation zone affect the evolution of flash floods. Moreover, bridge blockage from debris accumulation was methodically investigated under multiple return periods. Results indicated that during the two historical floods, the bridges altered the distribution pattern of flash floods from various flood elements, including the backwater effect, flow velocity, and inundation. It is noteworthy that the spillway bridge (M1) notably raised water levels and slowed flows, whereas the influence of other bridges on flood dynamics was more muted. The presence of six bridges resulted in expanded flooded areas, particularly near the upstream bridges, raising risks for Qishi Village. Furthermore, the increasing blockage ratios at bridge B2 during multiple return periods exacerbated the impacts on flood elements, consequently amplifying the disaster of flash floods. This research strongly emphasizes the importance of incorporating bridges and their blockages into flood risk management. It further provides technical insights to bolster the basin's resilience against extreme hydrological events.