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UBC Theses and Dissertations

Controls over experimental gravel-bed morphodynamics : the roles of coupling, form-process feedbacks and the lateral boundary Booker, William Henry


The morphodynamics of rivers are controlled by their boundary conditions, form-process feedbacks, and intrinsic thresholds of stability. Various classification systems have been developed to distinguish between types of morphodynamics, such that we may separate natural kinds of channels based on their differences in process. However, the effectiveness of our existing tools is limited where distinction between process is more subtle. To address this issue, my thesis develops new methods to examine process and its spatial distribution using a series of physical experiments. First, I developed a method to distinguish between the reach averaged morphodynamics of experimental channels. Over the course of the experiment, two systems substantially diverged in their behaviour due to the difference in their degrees of freedom; the ability to adjust width. The index that was developed to demonstrate the differences between these channels indicates the nature of deformation and considers the coupling between sediment transport and the change in channel morphology. Following on from this, both aspects used in the index's calculation - sediment transport and morphologic change - have a spatial variation in coupling as the interaction between bed load and the bed surface varies. Using these, I developed a spatialised index as a virtual velocity to demonstrate quantitatively how this variation in coupling influences morphodynamics along a pool-riffle sequence. This technique allowed for the spatial assessment of the influence of bank strength treatments on emergent morphodynamics over a series of floods and highlighted the potential application of an alternate coarse grain based style of treatment. Finally, I analysed the role that channel width and confinement play in the efficiency of sediment transport using these tools. Increases in width result in increasing degrees of work done to the channel that increases the coupling between sediment transport and channel change. Similarly, decreases in confinement allow for a greater degree of self-organisation and channel stabilisation, increasing the degree of coupling between sediment transport and morphologic change.

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