EFFECTS OF FLOW INTENSITY, OBSTACLE ALIGNMENT AND CROSS-SECTION GEOMETRY ON SCOUR AT BRIDGE ABUTMENTS

1 INTRODUCTION Local scour at bridge piers and abutments has long concerned engineers. Scour depth estimation has attracted considerable research interest and activity, and a number of prediction methods exist at present (see, e.g., comprehensive lists of predictors given by Melville and Colleman, 2000). Several studies have been completed since the 1950s for the particular case of scour at bridge abutments. Since the beginning of the 1980s, the University of Auckland, New Zealand, …

EFFECTS OF FLOW INTENSITY, OBSTACLE ALIGNMENT AND CROSS-SECTION GEOMETRY ON SCOUR AT BRIDGE ABUTMENTS

Experiments are reported on the effects of flow intensity, obstacle alignment and cross-section geometry on the equilibrium scour depth around abutments. The effect of flow intensity was studied for clear-water flow conditions, the obstacle alignment was studied for a wide range of angles of the obstacle with the flow direction, and tests on the cross-section geometry apply only to the case where the abutment extends into the main channel of a compound cross-section (two-stage channel). The channel bank and flood plain were built up with sand. The hypothesis of zero scour for flow velocities smaller than approximately 50% of the threshold velocity for the beginning of motion in the approaching flow cannot be rejected; maximum scour occurs for obstacles protruding at right angle from the cross-section walls, the reduction being small when obstacles point upstream; compared with rigid banks, the scour depth seems to be significantly reduced when channel bank and flood plain are constituted of alluvial material.