Preprints
https://doi.org/10.5194/egusphere-2022-53
https://doi.org/10.5194/egusphere-2022-53
 
05 Apr 2022
05 Apr 2022
Status: this preprint is open for discussion.

A comparison of 1D and 2D bedload transport functions under high excess shear stress conditions in laterally-constrained gravel-bed rivers: a laboratory study

David L. Adams1,2 and Brett C. Eaton1 David L. Adams and Brett C. Eaton
  • 1Department of Geography, University of British Columbia, Vancouver, BC, Canada
  • 2School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Australia

Abstract. Channel processes under high magnitude flow events are of central interest to river science and management as they may produce large volumes of sediment transport and geomorphic work. However, bedload transport processes under these conditions remain poorly understood due to data collection limitations and the prevalence of physical models that restrict feedbacks surrounding morphologic adjustment. The extension of mechanistic bedload transport equations to gravel-bed rivers has emphasised the importance of variance in both entraining (shear stress) and resisting (grain size) forces, especially at low excess shear stresses. Using a fixed-bank laboratory model, we tested the hypothesis that bedload transport in gravel-bed rivers collapses to a more simple 1D function (i.e., with mean shear stress and median grain size) under high excess shear stress conditions. Bedload transport was well predicted by the 1D equation based on the depth-slope product, whereas a 2D equation accounting for the variance in shear stresses did not substantially improve the correlation. Back-calculated critical dimensionless shear stress values were higher for the 2D approach, suggesting that it accounts for the relatively greater influence of high shear stresses, whereas the 1D approach assumes that the mean shear stress is sufficient to mobilise the median grain size. While the 2D approach may have a stronger conceptual basis, the 1D depth-slope product approach performs unreasonably well under high excess shear stress conditions. Further work is required to substantiate these findings in laterally adjustable channels.

David L. Adams and Brett C. Eaton

Status: open (until 17 May 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-53', Anonymous Referee #1, 06 May 2022 reply

David L. Adams and Brett C. Eaton

Data sets

Data accompanying submission to Earth Surface Dynamics David L. Adams https://doi.org/10.5281/zenodo.6360370

David L. Adams and Brett C. Eaton

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Short summary
Channel processes under flood conditions are important for river science and management as they involve high volumes of sediment transport and erosion. However, these processes remain poorly understood as the data is difficult to collect. Using a physical model of a river, we found that simple equations based on the mean shear stress and median grain size predicted sediment transport as accurately as ones that accounted for the full range of shear stresses.