Size of scallops and ripples formed by flowing water

Abstract

THE passage of water over a soluble solid wall often gives rise to intersecting polygonal depressions or horseshoe-shaped pits known as scallops and flutes1,2. The geometry of these surface deformations is remarkably reproducible in given flow conditions, but there is no generally agreed theoretical framework for predicting their characteristic dimensions, such as the spacing between successive transverse ridges. I present here indirect evidence in support of the hypothesis that the scalloping of soluble surfaces is due to the imprint of eddy patterns inherent in turbulent flow near a passive wall, and argue that small ripples on a granular bed may be formed in essentially the same way.