A New Bedform Stability Diagram, with Emphasis on the Transition of Ripples to Plane Bed in Flows over Fine Sand and Silt

  1. M. Marzo and
  2. C. Puigdefábregas
  1. J. H. Van Den Berg and
  2. A. Van Gelder

Published Online: 14 APR 2009

DOI: 10.1002/9781444303995.ch2

Alluvial Sedimentation

Alluvial Sedimentation

How to Cite

Van Den Berg, J. H. and Van Gelder, A. (2009) A New Bedform Stability Diagram, with Emphasis on the Transition of Ripples to Plane Bed in Flows over Fine Sand and Silt, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch2

Editor Information

  1. Barcelona, Spain

Author Information

  1. Institute of Physical Geography, Utrecht University, PO Box 80.115, Utrecht, The Netherlands

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 16 SEP 1993

ISBN Information

Print ISBN: 9780632035458

Online ISBN: 9781444303995

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Keywords:

  • transition of ripples to plane bed in flows;
  • constructive depositional bedform under unidirectional flow;
  • Ripple migration resulting in pattern of climbing ripples;
  • stability fields of bedforms under unidirectional currents;
  • particle mobility and grain size;
  • Non-equilibrium conditions result shift of the boundaries

Summary

Channel deposits of the Yellow River (China), composed of silt and very fine sands, show in cross-section ripple lamination, even lamination and small scour-and-fill structures.

Flume experiments with silt conducted to simulate Yellow River flow showed that the scour-and-fill structures represent cycles of erosion due to a process of irregular scouring followed by ripple drift sedimentation. Cohesion plays an important role in the generation of these cycles, which only occurred at conditions of overall equilibrium sediment transport. At high flow velocities the experiments showed the simultaneous occurrence of ripples, scours and plane bed. Similar transitional bed stages were found in results of previous flume studies, but have never been incorporated in bedform stability diagrams. In this paper a new bedform existence diagram for unidirectional flow is proposed using our data and a large number of previous flume and field data with siliciclastic sediments in the size range of 10–5100 µm. This diagram shows the stability fields of various bedform states, including the ripple and scour to plane bed transition as a function of a grain-roughness related mobility parameter and a dimensionless grain size parameter. The use of these parameters gives the diagram the advantage that it can be used without having any information on the alluvial roughness. Therefore this presentation is especially suitable in palaeoflow analysis of preserved sedimentary structures.