Local Scour at Skewed Piers

Dimensional analysis of the variables influencing local scour at skewed piers brings into issue the generality of skew factors apparently related only to skew angle, α, and pier aspect ratio, L/b, for a particular pier shape. This note discusses this issue and provides insights into flow-field and scour-geometry changes at skewed piers. It shows that the skew factor, Kα, as used in pier-scour equations to account for the influence on scour depth of pier orientation (skew) to flow, is influenced by parameters in addition to skew angle and pier aspect ratio. The parameters define the local flow field around the pier and determine the eventual scour depth and form in ways not fully taken into account by existing relationships for Kα. Those relationships, however, retain their usefulness as upper-bound envelopes for estimating Kα values for piers in comparatively shallow flows, especially for α less than about 45°.