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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Sediment management and morphodynamics : Morphodynamics in river confluences
Morphodynamics in river confluences
Author : SEBASTIÁN GUILLÉN-LUDEÑA(1) (2), MÁRIO J. FRANCA(2) ANTÓNIO H. CARDOSO(1) & ANTON J. SCHLEISS(2)
ABSTRACT
Within the fluvial network, confluences are considered particular areas in what concerns ecological connectivity, flood
safety and water quality. These characteristics were degraded in many cases, by previous channelization works, which
resulted in rivers with quasi-homogeneous hydro and morphodynamic conditions. To rehabilitate such impoverished
ecosystems, it is essential to deepen the knowledge about the confluence morphodynamic processes. These respond to
complex and three-dimensional patterns, which are influenced by parameters such as discharge and momentum flux
ratios, confluence angle, sediment grain size distribution, and bulk geometry. In addition, the existence of bed discordance
between the main channel and the tributary affects the main hydro-morphodynamic features in the confluence. This study
analyzes the effects caused on the confluence morphodynamics by discharge and momentum ratios, confluence angle,
grain size distribution, ratio of tributary to main-channel width (Bt / Bm), and local widening of the tributary mouth. For that
purpose 24 experimental tests, divided in 8 sets, were carried out in two laboratory confluences. Three discharge ratios
(Qr = 0.11; 0.15; 0.23) were tested in two different confluences in which the ratio of tributary to main-channel width was
Bt / Bm = 0.30 for the sets 1 to 6, and it was reduced to 0.15 by doubling the width of the main channel for the sets 7 and 8.
In the first two sets, the confluence angle was 90º whereas for the rest of the experiments the angle was 70º. All the
experiments were run under mobile bed condition by supplying sediment into both channels at constant but different rates
for each flume. For the sets 1 to 4, the supplied sediment were composed by two different poorly shorted mixtures of sand
and gravel with high gradation coefficients ( = 3.50 and 4.15), whereas for the sets 5 to 8 a more uniform sand ( = 1.40)
was supplied in both channels. Bed topography and water level were registered periodically during the tests duration and
the bed grain size distribution was analyzed at equilibrium. Differences in bed morphology and hydrodynamics together
with patterns of spatial distribution of bed sediment are summarized and discussed in this study.
File Size : 188,428 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Sediment management and morphodynamics
Date Published : 28/08/2015
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