What is scour, and why is it a leading cause of bridge failures in riverine environments?

• A. Erosion of sediment around foundations caused by flowing water; weakens foundations and can lead to sudden settlement or collapse
• B. Thermal expansion of foundation material
• C. Wind-induced oscillations
• D. Sediment deposition around foundations strengthening them

Answer: (A)

Scour is the erosion of sediment around bridge foundations caused by flowing water. In rivers, fast currents and turbulence at the base of piers and abutments remove soil around the foundations, creating scour holes and undermining the bearing capacity of the footing. As more sediment is washed away, the foundation loses support, leading to settlement, tilting, or even sudden collapse, especially during floods when flows are strongest. This mechanism directly attacks the foundation itself and can develop with little warning, which is why it’s a leading failure mode for bridges in river environments. Other factors like thermal expansion, wind-induced vibrations, or sediment deposition around foundations do not typically undermine the structure's support in the same persistent, adverse way.