Time Scale for Local Scour at Bridge Piers

TLDR

The study examines how clear‑water local scour depth develops over time around cylindrical bridge piers in uniform sand beds. The authors aim to quantify how flow duration affects local scour depth using new data. An equilibrium time scale (t*) is defined, and a method is provided to determine the time to reach equilibrium scour depth for a given pier, sediment, and flow velocity, enabling estimation of scour depth at any stage. The study finds that t* and equilibrium scour depth are similarly influenced by flow and sediment parameters, and that after 10 % of the equilibrium time the scour depth reaches roughly 50–80 % of its final value, depending on flow velocity.

Abstract

The temporal development of clear-water local scour depth at cylindrical bridge piers in uniform sand beds is considered. New data are presented and used to quantify the influence of flow duration on the depth of local scour. An equilibrium time scale (t*) is defined. The data show that both t* and the equilibrium scour depth (dse) are subject to similar influences of flow and sediment parameters, as might be expected because they are inherently interdependent. A method is given for determination of the time for development of dse for a given pier, sediment, and approach flow velocity and the concomitant estimation of the scour depth at any stage during development of the equilibrium scour hole. The results show that the scour depth after 10% of the time to equilibrium is between about 50% and 80% of the equilibrium scour depth, depending on the approach flow velocity.