Turbulent Sand Suspension over Dunes

  1. N. D. Smith3 and
  2. J. Rogers4
  1. R. Kostaschuk1 and
  2. P. Villard2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch1

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Kostaschuk, R. and Villard, P. (1999) Turbulent Sand Suspension over Dunes, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch1

Editor Information

  1. 3

    Department of Geosciences, 214 Bessey Hall, University of Nebraska, Lincoln, NE 68588-0340, USA

  2. 4

    Cape Town, South Africa

Author Information

  1. 1

    Department of Geography, University of Guelph, Guelph, Ontario, N1G 2W1, Canada

  2. 2

    Division of Science and Technology, Department of Geography, Tamaki Campus, University of Auckland, Private Bag 29019, Auckland, New Zealand

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 7 OCT 1999

ISBN Information

Print ISBN: 9780632053544

Online ISBN: 9781444304213

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Keywords:

  • fluvial sedimentology;
  • sediment transport and bedforms;
  • turbulent sand suspension over dunes;
  • flume studies - large, turbulent, coherent flow structures generated over dunes playing important role;
  • turbulence - fundamental characteristic of alluvial flows linked to geomorphological processes;
  • dunes in Fraser Estuary;
  • Kriging estimates pointing evenly spaced grid;
  • acoustic flow visualization showing dunes generating suspension structures;
  • acoustic profiler providing instantaneous ‘snapshots’ of strongly intermittent suspension events

Summary

Processes of sand suspension in rivers are poorly understood, but flume studies suggest that large, turbulent, coherent flow structures generated over dunes may play an important role. This study links field and flume studies by visualizing sand suspension over large dunes in the Fraser Estuary, Canada. An acoustic profiler provides nearly instantaneous ‘snapshots’ of strongly intermittent suspension events, and velocity and sand-concentration profiles are used to create time- and space-averaged contour maps of velocity and sand suspension. The acoustic images show suspension structures originating at crests and at lower stoss sides of dunes. The contour maps reveal turbulent structures, characterized by low velocity and high turbulence intensity, at the dune trough, the lower stoss side, the crest, and above the lee side downstream of the crest. High sand concentration and flux on the contour maps occur in a zone that originates close to the bed on the stoss side of the dune and extends downstream of the dune crest. A secondary zone occurs further above the bed. The acoustic images and contour maps show that sand is suspended in coherent flow structures characterized by low mean velocity and high turbulence intensity. These structures are interpreted as upwelling ejections generated at crests and lower stoss sides of dunes. The results of this study improve our understanding of sand suspension processes and have important implications for sand transport in large rivers.