Surface water types and sediment distribution patterns at the confluence of mega rivers: The Solimões‐Amazon and Negro Rivers junction

Abstract

Large river channel confluences are recognized as critical fluvial features because both intensive and extensive hydrophysical and geoecological processes take place at this interface. However, identifications of suspended sediment routing patterns through channel junctions and the roles of tributaries on downstream sediment transport in large rivers are still poorly explored. In this paper, we propose a remote sensing-based approach to characterize the spatiotemporal patterns of the postconfluence suspended sediment transport by mapping the surface water distribution in the ultimate example of large river confluence on Earth where distinct water types meet: The Solimões-Amazon (white water) and Negro (black water) rivers. The surface water types distribution was modeled for three different years: average hydrological condition (2007) and 2 years when extreme events occurred (drought-2005 and flood-2009). Amazonian surface water domination along the main channel is highest during the water discharge rising season. Surface water mixing along the main channel depends on the hydrological seasons with the highest mixed-homogenized area observed during water discharge peak season and the lowest during discharge rising season. Water mixture also depends on the yearly hydrological regime with the highest rates of water mixing in 2009, followed by 2005 and 2007. We conclude that the dominant mixing patterns observed in this study have been persistent over a decadal scale and the anabranching patterns contribute to avoid a faster mixing in a shorter distance. Our proposed approach can be applied to a variety of morphodynamic and environmental analyses in confluences of large rivers around the world.

Damming the rivers of the Amazon basin

“…The sediment regimes and geochemistry of Amazon tributaries differ according to the dominant geotectonic regions that they drain 15 . Andean or Andean-foreland are rich in suspended sediment and solute loads, and the water pH is near-neutral Cratonic rivers are characterized by low suspended load and pH, and often highly enriched in dissolved and particulate organic carbon.…”

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

“…During this period, the Solimões River is dominant and expands in a south-north direction, pushing the black waters of the Negro River to the left bank, with black waters disappearing from the surface level in some areas. This dominance was also described by [11]. The processes of expansion and retraction of the two rivers in terms of SSC values can be understood from the dynamics of the hydrological regime of the Solimões and Negro River system.…”

“…The velocity in the Solimões River (average 1.5 m·s −1 ) is two to three times greater that of the Negro River (average 0.4 m·s −1 ) [5,10]. Studies have shown that there are significant velocity changes in the first kilometer before the confluence [5,[10][11][12][13]. During the dry period, the Solimões River arrives the confluence at an 80 • angle and with a gradual increase in velocity to 2.5 m·s −1 .…”

“…Remote sensing techniques have been used to determine the spatial and temporal variability of water characteristics, such as suspended sediments, and dissolved organic carbon and chlorophyll, with good results [1,11,[14][15][16]. Martinez et al [14] and Espinoza et al [15] show that water characteristics influence radiance, depending on particle size and the concentration of material.…”

“…The spectroradiometer is a good indirect technique for measurement in the field because of ease of operation once it is calibrated [17]. Using Moderate Resolution Imaging Spectroradiometer (MODIS) images, Park and Latrubesse [11] investigated the Solimões-Negro confluence and showed the interrelationship between the white and black waters. That study, however, did not consider a field survey in concomitance with MODIS data obtained at the confluence during the hydrological regime.…”