Open channel confluences are common geographical structures in surface runoff. Most natural rivers originate from mountains and hills, flow into a main stream at confluences and finally head into the sea. Confluences are major sites for a main stream to obtain sediment and water from a tributary. Complex turbulence structures such as vortices, flow stagnation, secondary flow, flow re-circulation and water exchange both in vertical and lateral directions result in complicated sedimentation, erosion, mixing and contaminant transport at open channel confluences. The detailed study of flow dynamics and morphodynamics in confluences is of great significance to the urban flood control, scour of the river bed, design and maintenance of the channel and sediment and pollutants transport. This thesis describes a novel flume experiment on the sediment transport patterns in channel confluences as a function of different flow and geometry conditions. The initial equilibrium bed geometry was developed in a mobile bed confluence flume under four cases including two junction angles and two discharge ratios. The equilibrium bed was fixed for each case allowing for detailed flow velocimetry. The observed spatial patterns of turbulence statistics are evaluated with respect to the equilibrium bathymetry. Sediment were then fed instantaneously to the tributary channel at three different feeding sites in order to study the sediment deposition patterns. It was observed that although the sediment initiated at different feeding sites move along different paths through the confluence, all sediment tend to deposit at the face of the dune in the flow separation zone. This thesis also investigated how the deposition pattern would change versus time when feeding at the same site from the tributary channel. The time history of deposition pattern was also investigated for one of the cases. The sediment that initially deposit at the face of the dune eventually moved to the back of the dune and deposit around the post-confluence scour hole, demonstrating that over time the deposition pattern evolves to a state which is similar with the original bed morphology.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/38582 |
| Date | 17 December 2018 |
| Creators | Yu, Qingcheng |
| Contributors | Rennie, Colin |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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