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Quantifying the processes of fine sediment conveyance and siltation in river channels, Centre for Ecology and Hydrology , UK
Supervisory team: Dr Gareth Old (Centre for Ecology & Hydrology, gho@ceh.ac.uk), Dr P Rameshwaran (Centre for Ecology & Hydrology, ponr@ceh.ac.uk) and Professor David Sear (Geography & Environment, University of Southampton, D.Sear@soton.ac.uk). 
 
The student will be registered at the University of Southampton and hosted at Centre for Ecology & Hydrology (Wallingford). 
 
Although fine sediment is a fundamental component of river habitat and a vital measure of geomorphic work at the catchment scale, increased loading of fine sediment to rivers due to intensification of agriculture and, its impacts on biota are of growing global concern. This is particularly important in an era of increasing population and extreme hydrological events. Evaluating river bed sediment budgets by quantifying the processes that trap and release fine sediments within the river network is essential to understanding fine sediment transfer, supporting river management and model development. This research is timely as it is closely aligned with the topical paradigm of Working With Natural Processes (WWNP). 

Hydrological events, local hydraulics, plant growth and management are all key components in the seasonal trapping, production and release of fine sediments. However, there is still limited process understanding and quantification of (i) storage and release mechanisms of fine sediment within the river bed (ii) trapping efficiencies of different types of bed substrate, (iii) role of biofilms and macrophytes, and (iv) distance travelled by fine sediment once released. The proposed project builds on current research expertise at CEH focused on both experimental and field measurements and the development of three-dimensional hydraulic modelling. 
 
These gaps will be addressed through detailed field measurements in rivers with contrasting hydrological regimes (i.e. ground and surface water dominated). Probable field sites include the CEH River Lambourn Observatory, Berkshire and the New Forest Research Catchment (University of Southampton), Hampshire. In the field, there is opportunity to develop and use novel sampling techniques to quantify the amounts and quality of fine sediment stored in bed areas with different hydraulic characteristics and the production and storage of fine material within macrophyte stands, including their release during weed cuts. Detailed maps of vegetation and its growth are likely to be produced from aerial images collected using a drone. Targeted hydraulic measurements will be made using Acoustic Doppler Velocimetry (ADV) and Acoustic Doppler Current Profiling (ADCP). The fine sediment content of river gravels will be quantified using a disturbance technique whereas the rate of accumulation will be determined using gravel filled traps. The physical quality of deposited sediment (including its laser derived size distribution) will be determined in the laboratory. Novel measurements of sediment storage in macrophytes present a challenge to develop a new sampling method. State of the art insitu river monitoring will be used to determine suspended sediment concentration and its particle size distribution. 
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