Preprints
https://doi.org/10.5194/egusphere-2023-2348
https://doi.org/10.5194/egusphere-2023-2348
11 Jan 2024
 | 11 Jan 2024
Status: this preprint is open for discussion.

River suspended-sand flux computation with uncertainty estimation, using water samples and high-resolution ADCP measurements

Jessica Laible, Guillaume Dramais, Jérôme Le Coz, Blaise Calmel, Benoît Camenen, David J. Topping, William Santini, Gilles Pierrefeu, and François Lauters

Abstract. Measuring suspended-sand fluxes in rivers remains a scientific challenge due to their high spatial and temporal variability. To capture the vertical and lateral gradients of concentration in the cross section, measurements with point samples are performed. However, the uncertainty related to these measurements is rarely evaluated, as few studies of the major sources of error exist. Therefore, the aim of this study is to develop a method determining the cross sectional sand flux and estimating its uncertainty. This SDC (for Sand Discharge Computing) method combines suspended-sand concentrations from point samples with ADCP (Acoustic Doppler Current Profiler) high-resolution depth and velocity measurements. The MAP (for Multitransect Averaged Profile) method allows to obtain an average of several ADCP transects on a regular grid, including the unmeasured areas. The suspended-sand concentrations are integrated vertically by fitting a theoretical exponential suspended-sand profile to the data using Bayesian modelling. The lateral integration is based on the water depth as a proxy for the local bed shear stress to evaluate the bed concentration and sediment diffusion along the river cross-section to evaluate the bed concentration and sediment diffusion along the river cross-section. The estimation of uncertainty combines ISO standards and semi-empirical methods with a Bayesian approach to estimate the uncertainty due to the vertical integration. The new method is applied to data collected in four rivers under various hydro-sedimentary conditions: the Colorado, Rhône, Isère and Amazon Rivers, with computed flux uncertainties ranging between 18 and 32 %. The relative difference between the suspended-sand flux in 21 cases calculated with the proposed SDC method compared to the ISO 4363 method ranges between -16 and +3 %. This method, which comes with a flexible, open-source code, is the first proposing an applicable uncertainty estimation, that could be adapted to other flux computation methods.

Jessica Laible, Guillaume Dramais, Jérôme Le Coz, Blaise Calmel, Benoît Camenen, David J. Topping, William Santini, Gilles Pierrefeu, and François Lauters

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Jessica Laible, Guillaume Dramais, Jérôme Le Coz, Blaise Calmel, Benoît Camenen, David J. Topping, William Santini, Gilles Pierrefeu, and François Lauters

Data sets

Suspended sediment measurements in the Isère River at Grenoble Campus Jessica Laible, Benoît Camenen, Jérôme Le Coz, Guillaume Dramais, François Lauters, and Gilles Pierrefeu https://doi.org/10.57745/YTCYSX

Data set of solid gaugings in several rivers Jessica Laible, Guillaume Dramais, Benoît Camenen, Jérôme Le Coz, David J. Topping, William Santini, and Gilles Pierrefeu https://doi.org/10.57745/NLFT7Q

Model code and software

Analysis solid gauging Jessica Laible, Blaise Calmel, and Guillaume Dramais https://gitlab.irstea.fr/jessica.laible/analysis-solid-gauging

Jessica Laible, Guillaume Dramais, Jérôme Le Coz, Blaise Calmel, Benoît Camenen, David J. Topping, William Santini, Gilles Pierrefeu, and François Lauters

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Short summary
Suspended-sand fluxes in rivers vary with time and space, complicating their measurement. The proposed method captures the vertical and lateral variations of suspended-sand concentration throughout a river cross section. It merges water samples taken at various positions throughout the cross section with high-resolution acoustic velocity and discharge measurements. The method also determines the sand flux uncertainty and can be easily applied to other sites using the available open-source code.