Entrainment of Spheres: An Experimental Study of Relative Size and Clustering Effects

  1. M. Marzo and
  2. C. Puigdefábregas
  1. C. S. James

Published Online: 14 APR 2009

DOI: 10.1002/9781444303995.ch1

Alluvial Sedimentation

Alluvial Sedimentation

How to Cite

James, C. S. (1993) Entrainment of Spheres: An Experimental Study of Relative Size and Clustering Effects, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch1

Editor Information

  1. Barcelona, Spain

Author Information

  1. Department of Civil Engineering, University of the Witwatersrand, PO Wits 2050, South Africa

Publication History

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

ISBN Information

Print ISBN: 9780632035458

Online ISBN: 9781444303995



  • Entrainment of spheres;
  • Cluster geometries;
  • the entrainment for spheres under known and well-controlled conditions;
  • effect of relative size is consistent with observations of natural sediments;
  • generally more susceptible to entrainment than single spheres;
  • Stability is least when arranged in line transverse to the flow direction;
  • greatest when shielded from upstream and obstructed from movement downstream


Entrainment of sediment particles is governed by fluid, flow and particle characteristics. A series of experiments was performed on spherical particles to study the effects of relative size under well-controlled conditions which standardized particle shape and bed geometry. The effect of particle size relative to bed roughness on the dimensionless critical shear stress required for entrainment was found to be consistent with incipient motion data for natural sediments. Experiments were also performed to investigate the effect on entrainment of the proximity of other particles in various clustering arrangements. In general, clusters were found to break up at lower shear stresses than required to move single particles but one arrangement was distinctly more stable than single particles.