|Background to the Project
The morphology of rivers is both the 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 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, sediment transport is highly unsteady, intermittent 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 forms and sizes, but are most sensitively tuned and least understood in large braided rivers, common to the world’s piedmont regions.
Many of these rivers are now heavily under pressure, no more so than in New Zealand, where they mined for the rich water and sediment resources they yield from their mountain sources. This has 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.
Recent aggradation at the Rees River bridge has reduced the freeboard to less than 2 m