Ripples on Stream Bed

Abstract

Some 30 years ago, John F. Kennedy laid the foundations for the description of the geometry of sand waves on stream beds by the potential flow model. Since then, the analysis has been extensively refined and extended, but no rigorous description of the small features, called ripples, exists. The present study attempts a “stock-taking” of the data and the various behavioral concepts with the aim of encouraging researchers to improve our knowledge of the physics of features called ripples. Various trends are identified from the data. It is deduced that ripples act as roughness elements of the boundary. The ripple troughs are “filled” with the energy-consuming lee vortices. The main flow is over the ripple crests and lee vortices and does not interact with the bed geometry. The “roughness layer” of ripples and vortices is within the constant shear layer and is affected by the flow depth only as far as it affects the velocity distribution and alters the shear stress on the bed.