Effect of bed elevation discordance in the main river on the confluence hydrodynamics in 90 degrees straight-channels' confluences

Abstract

A role of the difference in bed elevations in the main-river (Delta z(MR)) at its entrance to a 90 degrees straight-channels' confluence is studied numerically using a 3D finite-volume model. Three characteristic hydrological scenarios with D-R = {0.250, 0.583, 0.750} are analysed in four confluence layouts having Delta z(MR)/hd is an element of[ 0.0, 0.50] (where h(d) stands for the flow depth in the deeper canal at the confluence). It is found that: 1) a portion of the tributary flow in the bottom layers is entrained by the bed-step, 2) the w-velocity has the same order of magnitude as V-xy for Delta z(MR) >= 0.25 h(d) and D-R gt 0.5, 3) the opposite bank is endangered by erosion due to strong upward motion along this bank, 4) additional shear layer develops on the outer side of the distorted u(max)-core and 5) the presence of bed-step favours bed-load transport both in and far downstream of the confluence.