Hyperscale Modelling of Braided rivers: Linking Morphology, Sedimentology and Sediment Transport

The morphology of rivers is both a cause and consequence of sediment transport occurring episodically during floods. Understanding this feedback has been the focus of river geomorphology for nearly a century and reflects the importance of these interrelated controls on flood conveyance, bank erosion, engineering structures, as well as river ecology and resource management. However, unlike the flood flows which drive this system, the conveyance of sediment through rivers is intermittent, highly unsteady and spatially variable, so that predicting the linked patterns and timescales of channel adjustment remains a continuing challenge for both scientists and river managers alike. These problems affect rivers of all styles and scales, but are most sensitively tuned and least understood in large braided rivers, common to the world's piedmont regions. Many such rivers are now heavily under pressure, mined for the rich water and sediment resources they yield from their mountain sources, but with increasingly uncertain implications for the health of their ecosystems and flood hazards. Despite this, the basic task of quantifying their sediment dynamics in order to predict changes in their morphology and vice versa, remains problematic and has hindered the development of a general theory linking channel form and sediment transport to flood characteristics. In this research we bring to together an international team of river scientists with skills in remote sensing, hydrometry and sedimentology to develop novel methods to link the patterns of river channel change in braided rivers to the flood flows that drive them. Working on a prototype braided system in New Zealand, the Rees River, this project has two principal aims: [1] to develop the first hyperscale models of a large, piedmont braided river which captures and quantifies the evolution of the system during an entire flood season; and [2] using this unique dataset, to link patterns of channel morphology, bed surface sedimentology and sediment transport, to the driving control of river discharge and the associated local hydraulic forces. We will do this by developing next-generation terrestrial laser scanning technology and low-altitude photography to generate digital models which represent the form and composition of rivers from the scale of the individual grains upwards. These data will allow us to answer key questions including: how do patterns of sediment transport vary with flood flows?; how does the distribution of riverbed facies and structures influence transport rates?; and what are the principal sources of uncertainty in estimated sediment transport rates? The answers to these questions will create a step-forward in the development of robust science-led strategies to better manage the resources of these unique intra-montane and piedmont river systems.