Eur. Phys. J. E 8, 465-476 (2002)
Long-time behavior of sand ripples induced by water shear flowA. Betat1, C.A. Kruelle1, V. Frette1, 2 and I. Rehberg1
1 Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth, Germany
2 Department of Engineering, Stord/Haugesund College, Bjørnsonsgt. 45, N-5528 Haugesund, Norway
(Received 9 March 2001 and Received in final form 2 July 2002 Online publication 8 October 2002)
The formation of sand ripples under water shear flow in a narrow annular channel and the approach of the ripple pattern towards a steady state were studied experimentally. Four results are obtained: i) The mean amplitude, the average drift velocity and the mean sediment transport rate of the evolving bed shape are strongly related. A quantitative characterization of this relation is given. ii) The ripple pattern reaches a stationary state with a finite ripple amplitude and wavelength. The time needed to reach the state depends on the shear stress and may be several days. iii) The onset of ripple formation is determined by the bed shear stress, but it seems neither to depend on the grain diameter nor on the depth of the water layer. iv) The ripple amplitude, drift velocity and sediment transport in this stationary state depend on the grain size. This dependency is neither captured by the particle Reynolds number nor by the Shields parameter: an empirical scaling law is presented instead.
45.70.-n - Granular systems.
92.10.Wa - Sediment transport.
92.40.Gc - Erosion and sedimentation.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002