A CFD-based critical-velocity threshold framework for flood resilience assessment of vulnerable timber covered bridges

<title>Abstract</title> <p>This study examines Taixin Bridge in Fengkai County, Guangdong Province, to address the safety risks confronting vulnerable timber covered bridges under extreme hydrological conditions. We propose a cross-disciplinary assessment methodology that integrates computational fluid dynamics (CFD) simulation with architectural typological analysis, archival research, and field investigations. Through this approach, we establish that the bridge and its associated water conservancy system—dating back to the Ming Dynasty—constitute an integrated heritage ensemble. By reconstructing the original layout and operational regime of the irrigation system, the research reveals a mechanism of "functional symbiosis." Specifically, we reconstruct its symbiotic water-conservancy system and calculate pier-specific critical velocities of 3.14 m/s (overturning) and 5.34 m/s (sliding). CFD simulations across six hydraulic scenarios demonstrate that the irrigation infrastructure maintains pier-region velocities well below the overturning threshold even under 1,400 mm extreme water levels. In turn, the bridge system supports agricultural water regulation and conveyance. Ultimately, this functional symbiosis mechanism provides a transferable safety assessment framework for analogous heritage bridges, providing crucial quantifiable evidence for their preventive conservation in an era of intensifying climate extremes.</p>