This study compares the total suspended sediment (TSS), total dissolved solids (TDS), and dissolved organic carbon (DOC) dynamics of two major inter-tropical rivers, the Congo in Central Africa and the Orinoco in South America, focusing on sampling undertaken during the period 2006-2010. Both rivers are characterized by similar mean annual discharges into the Atlantic Ocean, on its eastern and western margins, respectively. For both rivers, the results presented are placed in the context of the available longer-term hydrological time series (Congo: 1903(Congo: -2010 Orinoco: 1926 Orinoco: -2010. The key features of the recent records of material flux for both rivers were established and compared with other published data from the 20th century. The available discharge time series show that the rivers are characterized by similar maximum monthly discharges (Congo: 75 500 m 3 s -1 ; Orinoco: 85 500 m 3 s -1 ) and similar interannual variability (Congo: 1.69; Orinoco: 1.66). However, contrasts in low-flow regime (minimum low flows: Congo: 23 000 m 3 s -1 ; Orinoco: 2300 m 3 s -1 ) and seasonal variability (Congo: 3.3; Orinoco: 37.2), as well as in material fluxes were identified. Specific suspended sediment yields for the Orinoco (89 t km -2 yr -1 ) were very significantly higher than those for the Congo (9.4 t km -2 yr -1 ). These differences are mainly explained by contrasts in the physiographic characteristics of the two river basins, such as their contrasting relief. The differences between the TSS fluxes calculated for the Orinoco in this study and those indicated by published data from the second half of the 20th century can be explained by the impact of the hydroelectric dams built in the foothills of the Andean Cordillera. Changes in the TSS fluxes of the Congo are mainly explained by the impact of climatic change on total runoff.

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Multi‐annual contemporary flood event overbank sedimentation rates were quantified on the World's third largest river in terms of discharge, the tropical lower Orinoco. We discuss the role of variables at the basin and reach scales that contributed to the complexity of spatio‐temporal overbank sediment deposition patterns. Monitored in situ plots were characterized by distance to the main channel, hydroperiod, different geomorphological units, and vegetation cover. Flood event sedimentation rates showed a high spatial variability ranging from the absence of sediment deposition up to 225.46 kg m‐2 yr‐1. Banks and levees received relatively high amounts of sediment (39.6 kg m‐2 yr‐1), whereas observed mean sedimentation rates on the more distant floodplain and backswamps tended to be lower (17.7 kg m‐2 yr‐1). Significant differences in sedimentation rates were observed in two major vegetation types: dense herbaceous and shrubby vegetation (42.2 kg m‐2 yr‐1) and floodplain forest (12.7 kg m‐2 yr‐1). However, overbank sedimentation patterns also reflected imbricated hydrosedimentary and biogeomorphological vegetation feedbacks that co‐construct fluvial landforms. The incidence of an El Niño–Southern Oscillation–La Niña episode during the study period on sediment availability and floodplain sedimentation suggests that within whitewater rivers, where suspended sediment concentrations are naturally high, hydrological connectivity seems to be more important for floodplain sedimentation than variations in suspended sediment concentrations. These results may provide a good basis for future biogeomorphological investigation projects using complementary methodologies, in order to better anticipate global change and fluctuations in the occurrence, strength or duration of El Niño–La Niña episodes in the tropical zone and their consequences for flood discharge and sediment dynamics during channel–floodplain exchanges.

The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37 600 m 3 s −1 at its outlet to the Atlantic Ocean. Due to the presence of the Guiana Shield on the right bank, the lower reach of the Orinoco has a plan form characterized by contraction and expansion zones. Typical 1-1.5 km wide narrow reaches are followed by 7-8 km wide reaches. A complex pattern of bed aggradation and degradation processes takes place during the annual hydrological regime. A series of Acoustic Doppler Current Profiler (ADCP) transects were collected on an expansion channel in the Orinoco River, specifically over a fluvial island, representative of the lower Orinoco. In this study, temporal series of bathymetric cartography obtained by ADCP profiles combined with Differential Global Position System (DGPS) measurements (with dual-frequency), were used to recover the local displacement of bed forms in this island. The principal aims of this analysis were:(1) to understand the dynamics and evolution of sand waves and bars at this section and (2) to quantify the volume (erosion vs. accretion) of a mid-channel bar with dunes by applying DEM of Difference (DoD) maps on time series of bathymetric data. This required sampling with ADCP transects during the months of: May 2016; November 2016 and April 2017. Each bathymetric transect was measured twice, 1 day apart and on the same trajectory obtained by a GPS receptor. The spatial analysis of these ADCP transects is presented as a novel tool in the acquisition of time series of bathymetry for a relatively deep section (∼ 20 m) and under variable flow conditions.