Morphodynamics and sedimentology of gravel bed rivers

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The overall research goal is to analyze the morphology and dynamics of rivers and contribute to fundamental understanding of river landscapes and the sensitivity of rivers to environmental change. This requires an understanding of the processes that create particular types of river form and dynamics. At the heart of this is the idea that rivers are formed by their own processes of erosion, sediment transport and deposition, and that these processes form the bars, channels, and other features of the river landscape. The differences in the way these processes work is a primary cause of the variety of river forms seen in the landscape. The conventional approach to analyzing sediment transport in rivers is as a hydraulically-driven conveyor belt process, but this conception does not directly explain differences in river form and the local processes creating this form. I am exploring an alternative but complementary approach which considers sediment movement and the dynamics of the river form as essentially the same process, and so focuses on the dynamics of the river bed topography to look at the way that rivers actually work as dynamic landforms. Energetic, multi-channel, braided rivers, common in mountain and foothills areas, are a useful river type in which to test this approach because they continuously change and reconfigure their morphology, especially during high flow events. The goal is to examine the processes by which these morphological changes happen, quantify the rates of change and their differences over time, connect these morphological changes to the rates of bed material transport, and compare rivers of differing morphology and sedimentary features. In short, to understand how these rivers function as dynamic landforms. At the same time, the intent is to develop new methods for characterizing and predicting sediment transport rate in rivers based on the dynamics of river form. Because morphological dynamics of rivers is relatively slow we use small-scale physical models in an experimental flume to speed up the processes, control the conditions, observe the development of channel morphology, measure rates of change and the volumes of erosion and deposition (using photogrammetry to map bed topography), monitor rates of sediment transport and observe the way in which morphology develops from the statistics of bed material particle movement. The model data are validated using field data. The outcome will be the further development of this morphodynamic analysis directly connecting river morphology and sediment transport, and especially a quantitative understanding of differences in river morphology and `styles' of river dynamics. This provides a more complete picture of river dynamics from which to anticipate the effects of changes imposed on rivers by various environmental changes, engineering or flow manipulation, and also a basis for assessing geomorphic quality and for restoring river morphology and dynamics.