Modeling Local Scour Dynamics to Assess Existing Bridge Resilience in the Context of Climate Change

River crossings are vulnerable to extreme flood events, which pose significant risks to both linear infrastructure functioning and surrounding communities. The proper functioning of bridges is crucial for preventing cascading effects on populations, ensuring the mobility of emergency response teams, and facilitating the evacuation of residents during critical events. As vital links between communities on opposite banks of the river, bridge safety has significant implications for social and economic stability.

Hydraulic phenomena account for over 50% of bridge failures (e.g. Xiong et al., 2023), and scouring around piers and abutments always causes serious damages if adequate foundation depth is not provided in the design. Lacks in scientific and technical knowledges have led in the past to inadequate piers and foundations, and this issue, combined with the increased frequency of hazardous events due to the climate change, amplifies the risk of failure.

A robust prediction of scour evolution up to its maximum depth is fundamental for understanding and forecasting bridge failures, as well as for properly managing infrastructure in the context of climate change. Here, the physical processes governing scour evolution, specifically the temporal behavior of flow field and shear stress, have been thoroughly analyzed by combining physical modeling of sediment-flow-structures interaction with numerical simulations.

The experiments have been developed in a rectangular flume 1 m wide and 15 m long, using quite uniform sands (median grain size d₅₀=0.4 mm) to simulate the riverbed. Experiments of different duration were developed under steady state clear water conditions and adhering to Shields similitude to obtain the scour evolution over time around circular piers. Numerical simulations were developed using 3D CFD software to accurately reproduce the coherent turbulent structures around the pier at scour depths obtained from physical experiments.

This approach, combining and interconnecting physical and numerical experiments, enhances our understanding of how climate change and the consequent increase in flood event frequency impact on the temporal evolution of flow field and shear stresses as the scour progresses. This improved comprehension of the phenomena is crucial for the management of existing bridges that may have been inadequately designed in the past, as well as for the design of new structures.