Role of upstream planform curvature at asymmetrical river confluences–laboratory experiment revisited

Abstract

River confluence hydrodynamics is influenced by different controls such as the junction angle, bed elevation discordance between incoming streams, upstream planform curvature, momentum ratio values of the confluent streams, as well as by the sediment composition of the river bed. Previous studies were mostly concerned with the analysis of individual or combined effects of the junction angle, bed elevation discordance and momentum ratio values. The role of upstream planform curvature was indeed recognised, but there were no attempts to investigate it either separately, or in combination with other examined controls. This paper addresses an issue of upstream planform curvature effect on the confluence hydrodynamics by means of a three-dimensional numerical model. Existing laboratory measurements in a single-flume confluence model are used for model validation. Both an individual and combined effect with the bed elevation discordance are analysed for a single momentum-ratio value. Results are discussed in terms of downstream (u) and vertical (w) velocity distributions at the confluence and in the post-confluence channel, and variations of flow and deviation angles along the junction-line at different elevations above the tributary bed.