Live‐bed Scour at Bridge Piers

The relationship between scour depth at cylindrical bridge piers founded in cohesionless sediments, and mean approach flow velocity is defined for flows above the threshold of particle motion. Experimental data are collected in which pier size, sediment size and mean approach flow velocity are systematically varied. These data show that the relationship between scour depth and flow velocity differs, depending on whether the bed sediment is ripple forming or non‐ripple forming, and separate functions are identified for each case. Both functions exhibit two scour peaks. These occur at the threshold and transition flat bed conditions. Contrary to previous findings, the maximum scour depth is found to occur at the transition flat bed condition in the case of ripple forming sands. For nonripple forming sediments, however, the maximum scour depth occurs at threshold condition.