The effect of suspended sediment concentration on the settling velocity of cohesive sediment in quiescent water |
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| Authors: | Zai-Jin You |
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| Institution: | Coastal Unit, Ecosystems Branch, Department of Infrastructure, Planning and Natural Resources, PO Box 2185, Dangar, NSW 2309, Australia |
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| Abstract: | A laboratory study was carried to qualitatively investigate the effect of suspended sediment concentration C on the settling velocity ws of cohesive sediment in quiescent water. A bay mud sample was mixed with water in a cylindrical container, and three optical back scatterance sensors were then used to measure suspended sediment concentrations of the mud–water mixture at three levels every 15 s for 5 h while sediments were settling in the quiescent water. Based on the measured sediment concentrations, the settling velocities at different concentrations were derived from the depth-integrated mass balance equation. This study has found that the settling velocity ws is independent of C in the free settling regime of C<0.3 g/l, and then increases nonlinearly with C in the enhanced settling regime of 0.3<C<4.3 g/l, and finally decreases sharply with C in the hindered settling regime of C>4.3 g/l. The maximum settling velocity occurs at C≈4.3 g/l and is about nine times faster than the settling velocity in the free settling regime. A single empirical formula is also proposed to calculate the settling velocities at different sediment concentrations. |
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| Keywords: | Cohesive sediment Settling velocity Suspended sediment concentration Free enhanced and hindered setting |
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