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Discussion papers
https://doi.org/10.5194/esurf-2019-67
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-67
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 17 Dec 2019

Submitted as: research article | 17 Dec 2019

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This preprint is currently under review for the journal ESurf.

Entrainment and suspension of sand and gravel

Jan de Leeuw1, Michael P. Lamb1, Gary Parker2,3, Andrew J. Moodie4, Daniel Haught5, Jeremy G. Venditti5,6, and Jeffrey A. Nittrouer4 Jan de Leeuw et al.
  • 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
  • 2Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA
  • 3Department of Geology, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA
  • 4Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005
  • 5Department of Geography, Simon Fraser University, Burnaby, British Columbia, Canada
  • 6School of Environmental Science, Simon Fraser University, Burnaby, British Columbia, Canada

Abstract. Entrainment and suspension of sand and gravel is important for the evolution of rivers, deltas, coastal areas and submarine fans. The prediction of a vertical profile of suspended sediment concentration typically consists of assessing (1) the concentration near the bed using an entrainment relation and (2) the upward vertical distribution of sediment in the water column. Considerable uncertainty exists in regard to both of these steps, and especially the near-bed concentration. Most entrainment theories have been tested against limited grain-size specific data, and no relations have been evaluated for gravel suspension, which can be important in bedrock and mountain rivers, as well as powerful turbidity currents. To address these issues, we compiled a database with suspended sediment data from natural rivers and flume experiments, taking advantage of the increasing availability of high-resolution grain-size measurements. We evaluated 14 dimensionless parameters that may determine entrainment and suspension relations, and applied multivariate regression analysis. A best-fit two-parameter equation (r2 = 0.79) shows that near-bed entrainment, evaluated at 10 % of the flow depth, increases with the ratio of skin-friction shear velocity to settling velocity (u*skin / wsi), as in previous relations, and with Froude number (Fr), possibly due to its role in determining bedload-layer concentrations. We used the Rouse equation to predict concentration upward from the reference level, and evaluated the coefficient βi, which accounts for differences between turbulent diffusivities of sediment and momentum. The best-fit relation for βi (r2 = 0.40) indicates greater relative sediment diffusivities for rivers with greater flow resistance, possibly due to bed-form induced turbulence, and smaller u*skin / wsi; the latter effect makes the dependence of Rouse number on u*skin / wsi nonlinear, and therefore different from standard Rousean theory. In addition, we used empirical relations for gravel saltation to show that our relation for near-bed concentration also provides good predictions for coarse-grained sediment. The new relations are a significant improvement compared to previous work, extend the calibrated parameter space over a wider range in sediment sizes and flow conditions, and result in 95 % of concentration data predicted within a factor of nine.

Jan de Leeuw et al.

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Jan de Leeuw et al.

Jan de Leeuw et al.

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