Scour which occurs due to local flow changes in a channel caused by constrictions caused by the presence of bridge piers, abutments, etc. is called?

• A. Scour, Local
• B. Scour, General
• C. Erosion
• D. Local Erosion

Answer: (A)

When flow is constricted by a bridge pier or abutment, the current around the structure becomes locally disturbed, accelerating near-bed shear and generating vortices that remove sediment just at the base of the structure. This creates a deep, localized hollow—a local scour hole—around the foundations. It’s distinguished from scour that would occur along a longer stretch of the channel (global or general scour), which results from broader changes in flow conditions rather than the direct, localized impact of the structure. Erosion is a general term for wearing away of material and doesn’t specify the localized pattern around a bridge, and “local erosion” isn’t the standard terminology used for this phenomenon. Therefore, the term that best describes this situation is local scour.