3D Numerical Investigation Sediment transport and bed morphology at river channel confluences

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Mohammad Rostami, Marziye Sarvari

Tuesday 30 june 2015

17:00 - 17:15h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 7B. Sediment - River

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Confluence is the hydraulic singularity where two or more channels (or rivers) converge in a single channel downstream. In fluvial networks, stream channel confluences produce significant changes in flow, sediment transport and water quality. Although over the last 60 years, the synergy between laboratory tests and field measurements has provided valuable information about the complex hydro-morpho-sedimentary processes acting in river confluence zones, but less numerical study as a cost-effective tool has been conducted in this area. The objective of the present paper is to investigate in detail the changes in the hydro-morpho-sedimentary processes occurring in confluence zone using a numerical model. A 3D CFD commercial model selected for this study solves Navier-Stocks equations with finite volume method. Selected turbulence model is RNG _-_ model and the bed-load transport model is based on Shields number. In the absence of field data, experimental data for channel confluence collected in the laboratory were used to verify the simulated results. Experiments were performed in a confluence flume where the main channel is 8.5 m long and 0.50 m wide. A 4.9 m long and 0.15 m wide tributary channel is connected at an angle of 90°. Three discharge scenarios were tested. Numerical model was performed as the same geometry, flow and sediment data which used in experimental work. Satisfactory agreement was found between computed and measured flow pattern, bed load and bed elevation in the laboratory. The simulated bed profiles in the confluence zone compared well with the experimental data. The statistical analysis showed that in confidence level of 99%, numerical model with averaged coefficient of determination (R2) about 0.85 and an error of about less than 15 % might become a useful tool for predicting bed morphology changes including maximum depth of sediment deposit and maximum depth of bed erosion in river confluences.