The 'scour' at a bridge pier is caused by:
Choose the correct answer
Only during low-flow conditions
Horseshoe vortex at pier base + increased velocities in contracted waterway erode river bed material
Only from earthquake ground motion
Scour is beneficial for bridge safety
Correct Answer
B. Horseshoe vortex at pier base + increased velocities in contracted waterway erode river bed material
Why is this the answer?
Bridge pier scour: local erosion of river bed around pier due to increased flow velocities and horseshoe vortex formation at pier base. Types: (1) General scour (bed lowering from floods); (2) Contraction scour (narrowing of waterway between piers accelerates flow); (3) Local scour (horseshoe vortex at pier nose). Design: total scour = general + contraction + local. HEC-18 (US) / IS 3955 covers scour depth estimation.
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