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.

This paper summarizes many of the results from an extensive program of bridge scour research undertaken at The University of Auckland, New Zealand. An integrated approach to the estimation of local scour depth at bridge piers and abutments, collectively termed bridge foundations, is presented. The design method is based on empirical relations, termed K-factors, that account for the effects on scour depth of flow depth and foundation size, flow intensity, sediment characteristics, foundation type, shape and alignment, and approach channel geometry. The K-factors are evaluated by fitting envelope curves to existing data for piers and abutments and a new extensive data set for abutments. The new data are discussed and presented. Application of the design method is illustrated in examples.

Local scour around cylindrical bridge piers in uniform, cohesionless sediment was investigated experimentally. Three empirical functions which relate equilibrium scour depth with approach velocity, sediment size and How depth were obtained. The variations of equilibrium scour depth with approach velocity show that the depth of scour decreases at velocities just above the threshold until it reaches a minimum at about twice the threshold velocity. Thereafter, it increases again until a maximum is reached at the transition flat bed condition. At still higher velocity, the equilibrium scour depth decreases due to the formation of antidunes. Both the effects of sediment size and flow depth were found to be independent of the stage of bed particle motion and the approach velocity. Adjustment factors, for the effects of sediment size and flow depth were defined and evaluated.