Experimental study on characteristics of separation zone in confluence zones in rivers

Confluence zones in rivers are common occurrences in natural rivers, and their flow structures have a great impact on sediment transport and pollutant dispersion in confluence regions. Previous studies mainly focused on two-dimensional properties of the separation zone, and the studies of the variation of the separation zone from the water surface to the bottom are limited. Based on the confluence experiments carried out in a junction flume, the detailed characteristics of the separation zone were analyzed by using the commonly used streamline and the velocity isoline first proposed in this study, respectively. The velocity isoline method is conducted by the longitudinal velocity streamline considering its great impact on flow structure. Based on the analysis of the selected data from experiments, the geometry and the tendency of the separation zone present different forms with variations of distance to the flume bottom. Further, the discharge ratio also influences the separation zone from bed bottom to surface. © 2009 ASCE.