Which combination of countermeasures is commonly used to address scour risk around piers?

• A. Riprap only.
• B. Riprap armor, concrete aprons, grouted sleeves, and scour-depth monitoring with possible deep foundations extensions.
• C. Only deep-water dampers.
• D. Remove piers entirely.

Answer: (B)

Scour around piers happens when moving water removes sediment from around the foundation, especially at the toe and sides of the pile, which can undercut and destabilize the pier. The most reliable approach uses a layered set of countermeasures that protects the bed, the structure, and provides information to manage the risk over time. Riprap armor creates a rough, energy-dissipating surface that slows the flow near the bed and reduces the erosive forces acting on the sediment. A concrete apron extending downstream from the footing helps spread and calm the flow at the toe, further limiting the size of the scour hole and preventing a concentrated erosion path to the foundation. Grouted sleeves add a protective, stiff encasement around the exposed structural elements, guarding against abrasion and undermining by scour and seepage. Scour-depth monitoring gives real data on how deep the scour has progressed, so maintenance can be planned or the design adjusted if needed. In cases of severe scour, extending the foundations deeper into more resistant soil or rock can be necessary to maintain stability. Together, these measures address surface protection, toe protection, structural reinforcement, and ongoing assessment, which is why this comprehensive combination is commonly used. Riprap alone would not fully guard the toe or provide long-term monitoring and reinforcement, and removing piers or relying on a single measure would leave critical vulnerabilities.