The Morphology and Facies of Sandy Braided Rivers: Some Considerations of Scale Invariance

  1. Michael D. Blum6,
  2. Susan B. Marriott7 and
  3. Suzanne F. Leclair8
  1. Gregory H. Sambrook Smith1,
  2. Philip J. Ashworth2,
  3. James L. Best3,
  4. John Woodward3,† and
  5. Christopher J. Simpson4

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304350.ch9

Fluvial Sedimentology VII

Fluvial Sedimentology VII

How to Cite

Sambrook Smith, G. H., Ashworth, P. J., Best, J. L., Woodward, J. and Simpson, C. J. (2005) The Morphology and Facies of Sandy Braided Rivers: Some Considerations of Scale Invariance, in Fluvial Sedimentology VII (eds M. D. Blum, S. B. Marriott and S. F. Leclair), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304350.ch9

Editor Information

  1. 6

    Baton Rouge, Louisiana, USA

  2. 7

    School of Geography and Environmental Management, University of the West of England, Bristol BS16 1QY, UK

  3. 8

    Department of Earth and Environmental Sciences, Tulane University, Dimwiddie Hall, New Orleans, LA 70118, USA

Author Information

  1. 1

    School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK

  2. 2

    Division of Geography, School of the Environment, University of Brighton, Lewes Road, Sussex, BN2 4GJ, UK

  3. 3

    Earth and Biosphere Institute, School of Earth and Environment, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK

  4. 4

    Department of Geography, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, Canada

  1. Division of Geography, Northumbria University, Lipman Building, Newcastle upon Tyne NE1 8ST, UK

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 15 FEB 2005

Book Series:

  1. Special Publication Number 35 of the International Association of Sedimentologists

Book Series Editors:

  1. Ian Jarvis

Series Editor Information

  1. School of Earth Sciences and Geography, Centre for Earth and Environmental Science Research, Kingston University, Penrhyn Road, Kingston-upon-Thames KT1 2EE, UK

ISBN Information

Print ISBN: 9781405126519

Online ISBN: 9781444304350

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Keywords:

  • morphology and facies of sandy braided rivers;
  • scale invariance and surface morphology of braided rivers;
  • scale invariance in subsurface alluvial architecture;
  • Calamus River, Nebraska, USA;
  • South Saskatchewan River, Canada;
  • high-angle planar cross-stratification

Summary

A fundamental and unresolved question in fluvial sedimentology concerns the nature of scale invariance and whether it is appropriate to apply data from a single river or outcrop of alluvial sediments to others of a different size. This issue is addressed herein by: (i) examining the similarity in aspects of the morphology of modern braided rivers: (ii) comparing the subsurface facies of three sandy braided rivers of differing scale (30–2000 m channel width), as revealed by ground-penetrating radar (GPR). Measurement of braid-bar shape in 15 rivers, covering four orders of magnitude in spatial scale, demonstrates that a simple index of bar planform shape, the width : length ratio, is scale invariant. Additionally, scour depths at channel confluences are similar in their relative scale across channels of greatly differing size. Comparison of the subsurface sedimentary facies of three sandy braided rivers using GPR demonstrates that sandy braided rivers exhibit a degree of scale invariance, with the ubiquitous occurrence of trough cross-stratification associated with migrating dunes. Significant differences exist in the occurrence of other facies, however, both between rivers and between bars within the same river, most notably in the predominance of either high-angle planar cross-stratification or low-angle stratification. These differences are controlled by a wide range of factors, which may include the discharge regime, local bar and channel topography, anabranch width : depth ratio and the abundance of vegetation. Hence, although rivers and individual bars within the same river may have similar surface planform shapes, their subsurface facies may be very different. A single, universal facies model for sandy braided rivers is thus probably inappropriate and will remain elusive.