Measuring and modeling vertical gradients in suspended sediments in the Solimões/Amazon River

Abstract

International audienceAccurately measuring sediment flux in large rivers remains a challenge due to the spatial and temporal cross-sectional variability of suspended sediment concentrations in conjunction with sampling procedures that fail to accurately quantify these differences. This study presents a field campaign methodology that can be used to improve the measurement of suspended sediment concentrations in the Amazon River or similarly large rivers. The turbidity signal and Rouse model are together used in this study to define the spatial distribution of suspended sediment concentrations in a river cross-section, taking into account the different size fractions of the sediment. With this methodology, suspended sediment fluxes corresponding to each sediment class are defined with less uncertainty than with manual samples. This paper presents an application of this methodology during a field campaign at different gauging stations along a 3,000-km stretch of the Solimões/Amazon River during low water and flood periods. Vertical concentration profiles and Rouse model applications for distinctive sediment sizes are explored to determine concentration gradients throughout a cross-section of the river. The results show that coupling both turbidity technology and the Rouse model may improve our understanding of the spatial distribution of different sediments fractions sizes in the Solimões/Amazon River. These data are very useful in defining a pertinent monitoring strategy for suspended sediment concentrations in the challenging context of large rivers

Suspended Sediment Variability at the Solimões and Negro Confluence between May 2013 and February 2014

“…In Lake Catalão, near the Solimões-Negro confluence, there is an increase in the number of species between January and February because of the high concentration of nutrients. The peak of suspended sediments in the Solimões River was observed during these months [8].…”

Flow structure in large bedrock‐channels: The example of macroturbulent rapids, lower Mekong River, Southeast Asia

“…The bulges represent secondary flow strength and direction, with the latter inferred from deviation of the primary flow from the gravity gradient for all cross-sections. The irregular distribution of velocity with depth ( Figure 11) also has implications for estimating suspended sediment flux in large deep rivers using functions such as the Rouse profile (Armijos et al, 2017). Thus, the presence of distinctive flow filaments can be used to infer the patterns of transverse flow and the distribution of bed shear stress.…”

“…Thus, the existence of strongly defined velocity filaments below the water surface is a clear indication of relatively strongly developed secondary transverse flow circulation with implications for shear stress distribution, bedload transport and bedrock erosion. The irregular distribution of velocity with depth ( Figure 11) also has implications for estimating suspended sediment flux in large deep rivers using functions such as the Rouse profile (Armijos et al, 2017).…”

Rainfall control on Amazon sediment flux: synthesis from 20 years of monitoring

“…Since 1995, the Environmental Research Observatory (SO-Hybam) and national institutes from the Amazon basin have been working together to build a discharge and suspended sediments dataset to understand the dynamics of water and sediment fluxes in different parts of the Amazon basin. The sediment flux was also estimated through indirect methods, such as turbidity and MODIS images (Espinoza Villar et al (2013), Armijos et al 2017, Espinoza-Villar et al (2018), or by using the spatial and temporal variation of gravitational fields from GRACE satellite data (Mouyen et al 2018).…”

“…The Amazon River and its tributaries transport two well defined suspended sediment size fractions, which have different dynamics related to rainfall and discharge (Dunne et al 1998, Armijos et al 2017. Mertes and Meade (1985) showed that the bed forms are composed of dunes by 2 to 5 m in the Amazon River at Óbidos, and the particle size is between 125 to 500 μm in the Amazon River and its tributaries.…”