Bed sediment transport and channel morphology in a braided channel: insights from a flume experiment

Armstrong, Dylan L., author
Ettema, Robert, advisor
Nelson, Peter, committee member
Falkowski, Michael, committee member
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This thesis presents the methods and findings from an experiment aimed at relating the rate of bed-sediment transport through a reach of a braided channel to the intensity of the braiding sub-channels (anabranches) along the reach. The experiment was conducted in a large flume located at Colorado State University's Hydraulics Laboratory in Fort Collins, Colorado. No similar flume experiments have been conducted involving braided channels in a wide alluvial plain. Such experiments involve several challenging considerations that greatly complicate such experiments: braided channels are characteristically wide and shallow; have relatively large bed-sediment loads that are difficult to measure, because they move in multiple sub-channels; and the sub-channels (often termed anabranches) are ephemeral. The self-forming nature of the anabranches means that there is little direct control over the exact morphology of the braided channel. The objectives set forth in this experiment overcame the challenges of braided river flume studies, and allowed a comprehensive data set to be obtained of both bed sediment transport data and morphologic braided intensity data. The intensity of braiding was characterized using a braiding index (Flow Width Ratio) developed during this experiment. A relationship was identified and a trend established – as FWR increased, the rate of bed-sediment transport decreased – but the stochastic nature of transport rates and morphology introduced much scatter in the relationship. It was found that local morphologic features have a large impact on the transport of sediment through braided systems, and that the features could help explain some of the scatter in the data.
2017 Spring.
Includes bibliographical references.
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flume study
sediment transport
braided channel
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