ABSTRACT
The local scour at bridge piers has to be added to general scour and constriction scour to obtain the maximum scour depth for use in the design of bridge piers. The flow pattern past a pier protruding from a plane boundary in uniform open channel flow is complex. This complexity increases with the development of the scour hole. The flow separates at the sides of the pier and the separation surfaces enclose the wake downstream of the pier. Scour hole development commences at the sides of the cylinder with the holes rapidly propagating upstream around the perimeter of the cylinder to meet on the centreline. The large range of predicted and measured values of local scour depths at bridge piers, for what appear to be identical conditions, can be explained by the effects of a variety of specific parameters. The depth of local scour for all shapes of pier, except cylindrical, depends strongly on the alignment to flow.
