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Braided rivers, with their continuously changing network of channels, are highly dynamic systems.
Four mechanisms of channel change and evolution are considered the classic mechanisms of braided river formation: development of central bars, conversion of single transverse bars to mid-channel braid bars, formation of chutes, and dissection of multiple-braid bars.
There have been few studies on how each of these braiding mechanisms contributes to changes in sediment storage and to the dynamics of a river.
In one of the first field studies on the topic, Wheaton et al. analyzed repeat topographic surveys conducted over a 5-year period of the River Feshie, an active, braided, gravel-bed river in the United Kingdom.
They find that collectively, the four classic braiding mechanisms accounted for most of the change in sediment storage. However, their results highlight the critical role that bank erosion and other non-braiding mechanisms play in facilitating net increases in sediment storage by braiding mechanisms through providing an important local supply of sediment to feed those braiding mechanisms and through creating accommodation space where central bars can develop.
Source: Journal of Geophysical Research-Earth Surface, doi:10.1002/jgrf.20060, 2013 doi:10.1002/jgrf.20060 (Source: http://www.sciencecodex.com)
Morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel-bed river
- Joseph M. Wheaton1,*,
- James Brasington2,
- Stephen E. Darby3,
- Alan Kasprak1,
- David Sear3,
- Dami?Vericat4
Article first published online: 22 MAY 2013
DOI: 10.1002/jgrf.20060
Keywords:
- Glen Feshie;
- morphological sediment budgeting;
- DEM differencing;
- geomorphic change detection;
- braided river;
- dynamism
Abstract
[1] Previous flume-based research on braided channels has revealed four classic mechanisms that produce braiding: central bar development, chute cutoff, lobe dissection, and transverse bar conversion. The importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field. Here we exploit repeat topographic surveys of the braided River Feshie (UK) to explore the morphodynamic signatures of different mechanisms of change in sediment storage. Our results indicate that, when combined, the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach (61% total). Chute cutoff, traditionally thought of as an erosional braiding mechanism, appears to be the most common braiding mechanism in the study river, but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute. Three of the four classic mechanisms appeared to be largely net aggradational in nature, whereas secondary mechanisms (including bank erosion, channel incision, and bar sculpting) were primarily net erosional. Although the role of readily erodible banks in facilitating braiding is often conceptualized, we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms, and is the most important 搒econdary?mechanism (17% of total change). The results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings.
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