An index concentration method for suspended load monitoring in large rivers of the Amazonian foreland

Abstract

Because increasing climatic variability and anthropic pressures have affected the sediment dynamics of large tropical rivers, long-term sediment concentration series have become crucial for understanding the related socio-economic and environmental impacts. For operational and cost rationalization purposes, index concentrations are often sampled in the flow and used as a surrogate of the cross-sectional average concentration. However, in large rivers where suspended sands are responsible for vertical concentration gradients, this index method can induce large uncertainties in the matter fluxes. 20Assuming that physical laws describing the suspension of grains in turbulent flow are valid for large rivers, a simple formulation is derived to model the ratio ( ) between index and average concentrations. The model is validated using an exceptional dataset (1330 water samples, 249 concentration profiles, 88 particle size distributions (PSDs) and 494 discharge measurements) that was collected between 2010 and 2017 in the Amazonian foreland. The prediction requires the estimation of the Rouse number ( ), which summarizes the balance between the suspended particle settling and the turbulent lift, weighted 25 by the ratio of sediment to eddy diffusivity ( ). Two particle size groups, washload and sand, were considered to evaluate .Discrepancies were observed between the evaluated and measured , that were attributed to biases related to the settling and shear velocities estimations, but also to diffusivity ratios ≠ 1. An empirical expression taking into account these biases was then formulated to predict accurate estimates of , then (∆ = ±0.03) and finally .The proposed model is a powerful tool for optimizing the concentration sampling. It allows for detailed uncertainty analysis 30 on the average concentration derived from an index method. Finally, this model can be coupled with remote sensing and hydrological modeling to serve as a step toward the development of an integrated approach for assessing sediment fluxes in poorly monitored basins.Earth Surf. Dynam. Discuss., https://doi.

The sources and seasonal fluxes of particulate organic carbon in the Yellow River

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Intraseasonal‐to‐Interannual Analysis of Discharge and Suspended Sediment Concentration Time‐Series of the Upper Changjiang (Yangtze River)

“…This implies that most of the time (~ 95%) the mobile fine sediment is in the silt-clay grain size range and that the suspended concentration is uniformly distributed within the water volume (see Rhoads, 2020). This is an important assessment to be taken into account since as reported by previous authors in large rivers there is a strong variability of vertical SSC gradients as a function of sediment grain size (see Regüés &Nadal-Romero, 2013 andSantini et al, 2019) and also because of flocculation effects (see Lamb et al, 2020).…”

Sediment Flows in South America Supported by Daily Hydrologic‐Hydrodynamic Modeling

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