Dynamics of settling-driven convection beneath a sediment-laden buoyant overflow: Implications for the length-scale of deposition in lakes and the coastal ocean |
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| Authors: | Shahrzad Davarpanah Jazi Mathew G Wells |
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| Institution: | Department of Physical and Environmental Sciences, University of Toronto, 1065 Military Trail, M1C 1A4 Toronto, ON, Canada |
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| Abstract: | A series of laboratory experiments was conducted in order to determine how settling-driven convection influences the length-scale over which the majority of particles settle beneath a buoyant sediment-laden plume spreading over a denser saline layer. This system is analogous to sediment-laden river water spreading into a lake or the coastal ocean. The key dimensionless parameter that controls the settling dynamics of such flows is the density ratio, defined as the ratio of density differences due to the added salt and sediment. For a buoyant plume, this ratio has to be greater than unity, so that the experiments in the current study were performed for density ratios between one and five. When density ratio was close to one, settling-driven convection was vigorous and the length-scale over which sedimentation occurred was very small. A strong secondary turbidity current was generated in this case. On the other hand, for larger values of density ratio, the predicted length-scale over which a secondary plume was generated increased in proportion to the density ratio. A complete mathematical expression for this length-scale was developed using recent theory that described the timescale over which settling-driven convection evolved. The theoretically predicted propagation length-scale showed very good quantitative agreement with laboratory experiments. The use of the dimensionless density ratio allows the expression to predict which sediment-laden river plumes in lakes and the coastal ocean could quickly form secondary turbidity currents. |
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| Keywords: | Density ratio overflow sediment-laden gravity current settling-driven convection Stokes settling velocity turbidity currents |
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