PhD oppertunity is available in Leeds-UK

The influence of scale on flow dynamics in large river channels

Supervisors: Dr Daniel Parsons, Professor Jim Best, Dr Jeff Peakall, and Professor Phil Ashworth (Brighton)

The drainage basins of the World’s ten largest rivers amount to 17% of the global continental drainage area and deliver ~33% of the sediment load transported into the oceans. The way this vast water flow and sediment load moves through km-wide rivers is hugely important in determining flooding, bank failure, infrastructure collapse and ultimately creates the deposits that host some of the most lucrative mineral and hydrocarbon reserves. Despite the global importance of these rivers, our present knowledge-base relating to the morphology, flow dynamics and sedimentology of large rivers is wholly inadequate. A central weakness relates to how evidence derived from small rivers has been applied uncritically to rivers many orders of magnitude larger. We have good theoretical reason to question this transfer, since force balance considerations suggest a dependence on width-depth ratio that does not scale linearly with flow discharge. Furthermore, evidence is now emerging that the dominant processes and deposits of large rivers may be fundamentally different to currently accepted wisdom. Specifically, it has been noted that: (1) unit bars, currently thought to be the basic building block of all rivers may not be prevalent in the World’s largest rivers; (2) secondary flows and large-scale coherent flow structures in large rivers may be suppressed or even absent; and (3) these differences in process may lead to differences in flow routing, flow mixing, sediment movement and the subsurface sedimentology of large rivers.

This PhD project will be based on fieldwork on the Rio Paraná in Argentina, where focused ongoing field campaigns as part of NERC funded research are being used to investigate the dynamics of the one of the world’s largest river systems. The project will deploy a range of high-end hydrographic equipment including Multibeam Echo Sonar, acoustic Doppler profiling techniques to obtain a range of data on channel morphology (Figure 2) and flow structure, which will be used to examine key questions of how river channel processes scale with channel size. This PhD project will specifically examine flow structures through and over key units of the fluvial environment (bars, bends, bedforms) and the results will enable determination of the factors responsible for the breakdown in a scale invariant model of fluvial flow dynamics. This will include full examination of the relationship between bed roughness effects produced by bedforms of various scales, channel depth and channel width.

Entry requirements/necessary background: Minimum Upper Second Class degree (or equivalent) in Earth Sciences, Physical Geography, Engineering or Applied Mathematics.

Please see - http://www.see.leeds.ac.uk/study/phd/es-degrees.htm for further details or email d.parsons@see.leeds.ac.uk for an informal inquiry.