Temporal relations between meander deformation, water discharge and sediment fluxes in the floodplain of the Rio Beni (Bolivian Amazonia)

Abstract

International audienceThe Andean Cordillera and piedmont significantly influence river system and dynamics, being the source of many of the important rivers of the Amazon basin. The Beni River, whose upper sub-catchments drain the Andean and sub-Andean ranges, is a major tributary of the Madeira River. This study examines the river in the south-western Amazonian lowlands of Bolivia, where it develops mobile meanders. Channel migration, meander-bend morphology and ox-bow lakes are analysed at different temporal and spatial scales. The first part of this study was undertaken with the aim to link the erosion–deposition processes in the active channel with hydrological events. The quantification of annual erosion and deposi- tion areas shows high inter-annual and spatial variability. In this study, we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters (flood intensity, date of discharge peak and duration of the bank-full stage level). The second part of this study, focusing on the abandoned meanders, analyses the cutoff processes and the post-abandonment evolution during 1967–2001. This approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution

From source to sink: Preserving the cosmogenic 10Be-derived denudation rate signal of the Bolivian Andes in sediment of the Beni and Mamoré foreland basins

“…This possibility would require deep floodplain storage for very long periods (several Myr) in order for nuclides to decay from their original nuclide composition. However, Mamoré migration rates are comparable to those of the Beni River (Gautier et al, 2007), which means that sediment residence times do not exceed those observed in the Beni River case. Channel depths are only ~ 10 m, which makes the incorporation of deeply stored floodplain sediment to the main channel relatively unlikely.…”

“…From measuring suspended sediment concentrations in the Andean and floodplain Beni basin, Guyot (1993) and Guyot et al (1996) for example found that about half of the total sediment flux discharged from the Bolivian Andes is deposited in the adjacent Beni foreland basin. In these settings, the Beni and Mamoré Rivers have developed highly active meander river systems with migration rates of up to 30 m/yr (Gautier et al, 2007). High migration rates account for rapid sediment exchange between the river and the floodplain; Dosseto et al (2006) have estimated a residence time of sediment in the Beni floodplain between Rurrenabaque and the outlet of the Beni floodplain (at its confluence with the Mamoré, see Figure 1) of 4 -6 kyr by using U-series isotopes.…”

Cosmogenic nuclide budgeting of floodplain sediment transfer

“…The Beni River is an upper Amazon tributary; its floodplain is a thoroughly investigated system where modern migration rates, recent sediment discharge, and bank erosion rates are well known (Guyot et al, 1996;Aalto, 2002;Aalto et al, 2003;Gautier et al, 2007). 10 Be concentrations of Beni River floodplain sediment have also been investigated in detail (Wittmann, 2008).…”

Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

“…Likewise, it aims to identify the trend and evolution with time of the average annual rainfall in the basin countries. Within the framework of the Hydrology and Geodynamics of the Amazon Basin (HYBAM) programme, a rainfall variability analysis has been developed to assess the impact on discharge and sediment transport in the AB (Guyot, 1993;Gautier et al, 2006). This article first presents the data and the related spatial distribution, as well as an explanation of the different methods applied.…”