Morphological bedload transport rates

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Rivers transport part of their sediment load as bed load - the larger particles that move by rolling or bouncing along the river bed. Bed load is important to river morphology and dynamics because its spatial and temporal variation in rate is directly responsible for the formation of the features, such as pools, bars and islands, which are major elements of the geomorphology of many rivers. Similarly, bed load processes affect river dynamics, such as channel migration and rates of morphological change. This research is intended to contribute to understanding the variables that control bed load flux and, in particular, the way in which particle movement interacts with the morphology as the river migrates and changes its morphology. The goal is to describe the development of river morphology as the outcome of the particle transfer process. This is fundamental to understanding river dynamics and has direct application in mitigating erosion problems, understanding the effects of river processes and flow on in-stream habitat and in restoring rivers altered by engineering. It is difficult to measure the bed particle movement in the field but for gravel-bedded rivers many of the processes and features can be reproduced in small-scale physical models in a laboratory flume. We will use physical models to investigate the controls on bed particle dynamics (erosion/deposition frequency and transport distances) under various flow conditions and different channel morphologies to understand how the morphological features develop from the particle pathways and path lengths and, in turn, constrain those movements. We will measure particle movement using tracer particles and video cameras and use digital photogrammetry and image processing to derive river bed topography, topographic change over time and bed roughness and particle size data. It is possible that bed load transport is completely tied up in the dynamics of the bars and pools of the river rather than moving freely over those features ( as it is often conceived). If so, this creates an entirely new conceptual and theoretical picture of bed load transport processes and river channel dynamics.