Confined Meandering River Eddy Accretions: Sedimentology, Channel Geometry and Depositional Processes

  1. N. D. Smith2 and
  2. J. Rogers3
  1. L. M. Burge and
  2. D. G. Smith

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch9

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Burge, L. M. and Smith, D. G. (1999) Confined Meandering River Eddy Accretions: Sedimentology, Channel Geometry and Depositional Processes, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch9

Editor Information

  1. 2

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

  2. 3

    Cape Town, South Africa

Author Information

  1. Department of Geography, University of Calgary, Calgary, Alberta T2N 1N4, Canada

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:

  • confined meandering river Eddy accretions - sedimentology, channel geometry and depositional processes;
  • Eddy accretions occurring along margins of confined channel-meander belts;
  • Eddy accretions are one of the few remaining unstudied sedimentary deposits within meandering river systems;
  • Eddy-accretion deposits are difficult to access;
  • acoustic bottom profiling and flow velocity measurements;
  • lithofacies description and interpretations from vibracores;
  • lithofacies successions and cross-sectional profiles;
  • Eddy-accretion successions from kootenay and beaver rivers;
  • confined valley-fill architectural geometry

Summary

Eddy accretions occur along margins of confined channel-meander belts where unusually deep scours, eroded by river flow impacting valley sides at right angles, infill primarily with sand. In unconfined meanders (e.g. Mississippi River), eddy accretions can form where channels impinge against resistant valley sides (bedrock, diamicton, silt–clay) or silt–clay oxbow fills within the valley. In confined settings, eddy-accretion deposits commonly occupy 25% of the floodplain and form where the ratio of floodplain-width to channel-width varies between 5 and 10.

From vibracores in confined meandering river valleys, stratigraphical profiles indicate that eddy-accretion deposits are considerably thicker than adjacent point bars, e.g., 17 m versus 6 m and 9 m versus 5 m for the Kootenay and Beaver rivers, respectively. In confined valleys, cross-valley geometries of eddy-accretion and point-bar deposits resemble dumb-bells, thick on the ends but thin across the middle. In one case (Kootenay River), a single eddy-accretion fill consists of two upward-fining sequences: a pebbly channel lag that crudely fines upward to a mid-sequence thick silt, above which rests another sandy sequence on an erosive base, similar to the lower, but capped by a rooted overbank silt. This apparent double upward-fining succession could be misinterpreted as the product of two superimposed point-bar upward-fining sequences. Acoustic bottom profiles of unusually deep scour holes adjacent to eddy accretions confirm the great thickness of fills as compared with nearby point bars.