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Citation Wooldridge, CL and Hickin, EJ. 2005. Radar architecture and evolution of channel bars in wandering gravel-bed rivers: Fraser and Squamish Rivers, British Columbia, Canada. Journal of Sedimentary Research. 75:844-860.
Organization SFU
URL http://www.sfu.ca/~hickin/PDF%20Library/Wooldridge:Hickin2005.pdf
Abstract/Description or Keywords The alluvial architecture and evolution of two kilometer-scale
compound bars in the wandering gravel-bed Fraser and Squamish rivers,
British Columbia, Canada, are described. Integrating ground-penetrating
radar, bathymetry, and aerial photographs enables the internal architecture
to be linked to the evolution of the gravelly barforms over the previous 50
years. These linkages reveal the sedimentary mechanisms that formed the
various architectural packages within compound bars and unit bars. Growth
of compound bars is controlled by the accretion of unit bars onto discrete
segments along their gravelly edges. The attachment of unit bars deflects the
thalweg to impinge on and erode specific portions of bars and channel banks.
Bar growth leads to the stabilization of bars, vegetation colonization of bar
interiors, and island formation. It is the formation of islands, along with
channel avulsions, that maintains channel division in wandering rivers.
Seven styles of gravelly deposition are imaged in the alluvial architecture.
Vertical-accretion deposits formed from the deposition of gravelly bedload
sheets are the most common strata. A moderate abundance of slipface
deposits preserves high-relief bar margins. Lateral accretion dominates
point-bar deposits. Downstream-accretion deposits govern some phases of
down-bar growth. Partial and complete channel-fill and chute-fill deposits
are eroded into underlying sediments, as are scour-and-fill deposits.
Upstream-accretion deposits are uncommon.
A depositional model of gravelly channel bars in the two rivers is
presented and reveals that the architecture is made up of depositional styles
similar to those observed in braiding-river successions, although the
sedimentary packages are preserved in different proportions. Differences
in braiding-river and wandering-river sedimentology largely reflect the
relatively frequent migration of channels and bars in braiding rivers, which
preserve high proportions of channel fill and chute fill, and confluence scourand-fill
deposits. Conversely, the moderately stable island and channel
network in wandering rivers limits channel shifting and consequently
preserves a low number of channel fills. Moderate proportions of slipface
strata and coherent patterns of sand deposition along bar tops provide
evidence of comparatively uniform flow patterns in independent channel
segments divided by islands. These patterns of bar sedimentation and
channel shifting preserved in the alluvial architecture appear to be signature
characteristics of wandering rivers. The occurrence of similar architecture in
both the Fraser and Squamish rivers suggests that the model likely applies
to most wandering gravel-bed rivers.
Information Type article
Regional Watershed Lower Fraser, Howe Sound & Sunshine Coast
Sub-watershed if known
Aquifer #
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Project status complete
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