Effect of ice cover roughness on local scour around bridge piers.

In cold-region rivers, the formation of ice cover during winter markedly modifies the hydraulic conditions, leading to enhanced local scour around in-stream infrastructures such as bridge piers. To analyze the flow characteristics and maximum local scour depth around the pier under both open-channel and ice-covered conditions with varying roughness, both experimental methods and numerical simulations were employed in this study. The findings reveal that, under rough ice-covered flow conditions, the interaction of elevated bed shear stress and intensified turbulent kinetic energy contributes to an increased maximum scour depth around the pier. Under identical approaching flow conditions, when the ratio of ice cover roughness to bed roughness increases to 1.9, the increase in maximum local scour depth around the pier becomes less pronounced owing to the enhanced energy dissipation caused by the rough ice cover. A numerical model for local scour around the pier under open-channel flow and ice-covered flow conditions was developed by integrating the RNG k - ε turbulence model with the Meyer-Peter sediment transport equation. A new formula was developed to estimate the maximum local scour depth around bridge piers considering various ice cover roughness conditions. Comparison with existing formulas demonstrates that the proposed formula achieves the highest accuracy, offering a useful reference for the design of bridge foundations in ice-affected regions.