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Two major morphological phenomena in alluvial river confluences are the development of an avalanche face or faces at the entrance of one or both converging channels to the confluence, due to deposition of coarser sediments, and deepening of the scour hole in the post-confluence channel. The development of an avalanche face creates the difference in bed elevations between incoming and outgoing channels. Laboratory experiments in movable bed models of confluences showed, and bathimetric surveys in field confluences confirmed, that avalanche faces develop in both converging channels only in alluvial river confluences with large junction angles (α ≥ 45o). The effect of bed elevation discordance between the tributary and main channels was studied in the author’s previous papers. Another step in recognising controls to the complicated flow pattern in a river confluence is the analysis of the role of bed elevation discordance in the main river. This paper, thus, continues the line of previous studies by considering the effect of different extents of bed elevation discordance in the main river on the flow characteristics in the confluence hydrodynamics zone, namely: 1) on the flow deflection at the tributary entrance to the confluence, 2) on cross-sectional distributions of the three velocity components in the post-confluence channel and 3) on variations of the recirculation zone size throughout the flow depth. To facilitate comparison with previous studies and to follow the above mentioned findings regarding the limit junction angle, only the confluence with α = 90o is considered. Four values of the bed elevation discordance ratio ΔzMR / hd in the range [0.0; 0.5] are analysed (where ΔzMR stands for the difference in bed elevations between the stretches of the main river upstream and downstream of the upstream junction corner and hd stands for the flow depth in the main river at the confluence).


Session R15, 3-D Modeling Applications



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