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