High Resolution Modelling Of Flow And Sediment Entrainment At River Confluences

School of Geography, University of Leeds

Principal Investigator:

Dr CJ Keylock

Dates:

1st June 2002 – 31st May 2004

Grant:

Nuffield Foundation

Summary:

River confluences are important nodes within the drainage network of fluvial systems. The river system must suddenly adjust to a change in discharge, geometry and sedimentary characteristics and the flow dynamics are complex. Confluence bed scour has been observed to be five times the mean channel depth, and the mobilisation of such a large amount of sediment has important implications for changes in channel morphology and flow downstream.

In the last decade there has been a renewal of interest in confluence flow processes, but no published work has tried to model sediment erosion at confluences at the scale of the fluid vortices produced by the confluence flow processes. The aim of this research is to couple a validated large-eddy simulation of the fluid eddies to a bed-load sediment entrainment algorithm to predict patterns of sediment entrainment in the post-confluence region.

This project comprises of four stages:

• To produce a validated LES of the parallel channel confluence flow field.
• An exploration of the controls upon the confluence eddy shedding process for parallel channel confluences.
• To couple the validated LES to bed load entrainment model to determine to what extent the patterns of sediment movement can be replicated by the model.
• To introduce junction angle as a flow parameter. This will lead to results that are more applicable to the confluences observed in nature.