Variations in clear water scour geometry at piers of different effective widths

Abstract

The equilibrium scour geometry around a circular pier protruding vertically on a scoured channel bed was experimentally investigated. In order to conduct a comparative study, measurements within an equilibrium scour hole at a square pier, an equilateral triangular pier, and a at plate with sides, facing the approaching flow equaling the width of the circular pier were taken. Flow in an equilibrium scour hole under a clear water regime was considered for 4 separate tests. Tests were carried out for approaching flow having undisturbed constant flow depth greater than the pier width with a depth-averaged approaching flow velocity of about 68.2% representing the critical velocity of the uniform sand bed. It was observed that all the equilibrium dimensionless scour parameters, namely scour depth, length, width, area, and volume, depend on the effective pier width equal to the diameter of the smallest circumscribing circle of the pier. When the effective pier diameter increases and approaching flow depth is constant, scour parameters increase. Based on the results, some empirical equations are proposed for the scour depth, scour length, scour width, scour area, and scour volume. These equations may be utilized to estimate scour geometry in future studies.