The Influence of Aggradation Rate on Braided Alluvial Architecture: Field Study and Physical Scale-Modelling of the Ashburton River Gravels, Canterbury Plains, New Zealand

  1. N. D. Smith4 and
  2. J. Rogers5
  1. P. J. Ashworth1,
  2. J. L. Best2,
  3. J. Peakall1,2 and
  4. J. A. Lorsong3

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch24

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Ashworth, P. J., Best, J. L., Peakall, J. and Lorsong, J. A. (1999) The Influence of Aggradation Rate on Braided Alluvial Architecture: Field Study and Physical Scale-Modelling of the Ashburton River Gravels, Canterbury Plains, New Zealand, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch24

Editor Information

  1. 4

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

  2. 5

    Cape Town, South Africa

Author Information

  1. 1

    School of Geography, University of Leeds, Leeds, West Yorkshire LS2 9JT, UK

  2. 2

    School of Earth Sciences, University of Leeds, Leeds, West Yorkshire LS2 9JT, UK

  3. 3

    ARCO, El-Djazair Company, 2300 West Plano Parkway, Plano, Texas 7507, USA

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:

  • alluvial facies and architecture;
  • influence of aggradation rate on braided alluvial architecture;
  • Canterbury plains, on east coast of south island, New Zealand;
  • grain-size distributions for modern Ashburton river and Ashburton outcrop;
  • flume model and scaling details;
  • classification of field and flume braided alluvial architectur;
  • flume–field comparison;
  • effect of changing aggradation rate on alluvial architecture

Summary

Theoretical process-based models of braided alluvial architecture suggest that aggradation rate is a primary control on the geometry, stacking and heterogeneity of sedimentary deposits. This hypothesis is tested at the scale of the channel and bar using a combined field and flume modelling study, which quantifies the impact of a change in aggradation rate on the frequency of occurrence and geometry of the key depositional units that dominate coarse-grained, braided alluvial architecture. Aggradation of a 1 : 50 scale model of the braided Ashburton River, New Zealand, produces realistic alluvial architecture that closely corresponds to 7 km of logged field prototype outcrop. A twofold change in aggradation rate in the flume model and an order-of-magnitude change in the field outcrop, have no influence on the geometry and vertical distribution of fine- and coarse-grained depositional niches. Braided alluvial architecture at the channel scale therefore is determined by the local ‘instantaneous’ aggradation rate, related to individual flood events, rather than the long-term, regional aggradation rate.