Preprints
https://doi.org/10.5194/egusphere-2025-1271
https://doi.org/10.5194/egusphere-2025-1271
26 Mar 2025
 | 26 Mar 2025

Improving a multi-grain size total sediment load model through a new standardized reference shear stress for incipient motion and an adjusted saltation height description

Marine Le Minor, Dimitri Lague, Jamie Howarth, and Philippe Davy

Abstract. Modelling sediment transport is important to understand how fluvial systems respond to climatic change or other transient conditions such as catastrophic sediment release. In natural rivers, heterogeneity of sediment properties and variability of flow regime result in different modes of transport that all contribute to the total sediment load. Le Minor et al. (2022) presented a sediment transport law for rivers that extends from bed load to suspended load while being relevant for a wide range of grain sizes but not specifically addressing the case of a distribution of grain sizes, which must also consider the interactions between grain classes that are mainly important during the sediment erosion phase. If these interactions are not properly considered, the model overestimates transport rates compared to measured ones. We present a new formalism for the reference shear stress of multiple-size sediments, a parameter governing the onset of transport. We show that using a reference shear stress standardized across datasets improves transport rate predictions made with the model of Le Minor et al. (2022). We show that considering the bed roughness length as a reference transport height for single- and multiple-size sediments significantly improves transport rate predictions. We also suggest that, for multiple-size sediments where the bed surface is not fully mobile, the entrainment coefficient should include a dependency on the fraction of mobile grain sizes at the bed surface, although data are insufficient to add this effect in a definite parameterization. Therefore, using a standardized reference shear stress and a transport length adjusted with a common reference height across all sizes appear to be two critical ingredients of a fully functional multi grain-size total sediment load model based on the disequilibrium length. This adjusted model offers the potential to quantify grain-size specific sediment fluxes when different modes of transport may be observed simultaneously, paving the way for more informed numerical modelling of fluvial morphodynamics and sediment transfers.

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Marine Le Minor, Dimitri Lague, Jamie Howarth, and Philippe Davy

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1271', Maarten Kleinhans, 21 Apr 2025
  • RC2: 'Comment on egusphere-2025-1271', Peter Wilcock, 07 Jul 2025
  • AC1: 'Comment on egusphere-2025-1271', Marine Le Minor, 16 Jul 2025
  • AC2: 'Comment on egusphere-2025-1271 - Response to reviewers', Marine Le Minor, 06 Aug 2025

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1271', Maarten Kleinhans, 21 Apr 2025
  • RC2: 'Comment on egusphere-2025-1271', Peter Wilcock, 07 Jul 2025
  • AC1: 'Comment on egusphere-2025-1271', Marine Le Minor, 16 Jul 2025
  • AC2: 'Comment on egusphere-2025-1271 - Response to reviewers', Marine Le Minor, 06 Aug 2025
Marine Le Minor, Dimitri Lague, Jamie Howarth, and Philippe Davy

Data sets

Supporting data tables and Python scripts for the paper: "Improving a multi-grain size total sediment load model through a new standardized reference shear stress for incipient motion and an adjusted saltation height description" Marine Le Minor https://doi.org/10.5281/zenodo.15043113

Marine Le Minor, Dimitri Lague, Jamie Howarth, and Philippe Davy

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Short summary
In natural rivers, flow variability and sediment heterogeneity affect how sediment grains are transported. A unique law that predicts the total amount of sediment transportable by a river for a wide range of sediment mixtures and flow conditions exist but unclear trends remain. Two improvements of this law, a standardized onset of sediment transport and a common reference transport height across all sizes, appear to be critical to have a functional multi grain-size total sediment load.
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