ABSTRACT
A role of the difference in bed elevations in the main-river ( https://www.w3.org/1998/Math/MathML"> Δ z MR https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6969.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> ) at its entrance to a 90° straight-channels’ confluence is studied numerically using a 3D finite-volume model. Three characteristic hydrological scenarios with DR = {0.250,0.583,0.750} are analysed in four confluence layouts having https://www.w3.org/1998/Math/MathML"> Δ z MR / h d ∈ [ 0.0,0.50 ] https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6970.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> (where hd 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 https://www.w3.org/1998/Math/MathML"> V xy https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6971.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> for https://www.w3.org/1998/Math/MathML"> Δ z MR ≥ 0.25 h d https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6972.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> and https://www.w3.org/1998/Math/MathML"> D R > 0.5,3 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6973.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> ) 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 umax -core and 5) the presence of bed-step favours bed-load transport both in and far downstream of the confluence.
