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

P. J. Ashworth, J. L. Best, J. Peakall, J. A. Lorsong

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

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.

Original languageEnglish (US)
Title of host publicationFluvial Sedimentology VI
PublisherWiley-Blackwell
Pages331-346
Number of pages16
ISBN (Electronic)9781444304213
ISBN (Print)0632053542, 9780632053544
DOIs
StatePublished - Mar 17 2009
Externally publishedYes

Keywords

  • Alluvial facies and architecture
  • Canterbury plains, on east coast of south island, New Zealand
  • Classification of field and flume braided alluvial architectur
  • Effect of changing aggradation rate on alluvial architecture
  • Flume model and scaling details
  • Flume-field comparison
  • Grain-size distributions for modern Ashburton river and Ashburton outcrop
  • Influence of aggradation rate on braided alluvial architecture

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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