Bridge backwater due to vehicles blockage driven by flash floods

Flash floods frequently transport vehicles, causing bridge blockage that substantially increases upstream backwater rise and its spatial extent. To quantify this process, flume experiments were conducted, considering variations in vehicle type, vehicle number and approach flow Froude number. The results demonstrate that the front-to-rear weight distribution of a vehicle significantly influences its transport dynamics, with the lighter end tending to drift downstream. Both backwater rise and length are positively correlated with the blockage index, and this relationship is further quantified through fitted predictive equations. Compared to local backwater rise, which is highly sensitive to turbulence and localized flow fluctuations, the backwater length, as a spatial-scale parameter, exhibits smoother and more stable variations across different blockage scenarios. These findings provide experimental and theoretical support for assessing hydraulic risks at bridges due to vehicle blockage during flash floods, offering a foundation for disaster mitigation strategies and the design of resilient infrastructure.