Characterization of confluences of free meander trains at the upper Amazon basin

Most of the past studies on river confluences dynamics are based on a limited number of experimental and field data that mainly represent the morphodynamic, hydrodynamic and sedimentary processes of alluvial river channels with limited planform activity. Moreover, these studies are concentrated mainly around the confluence region. This novel contribution focuses on the study of the planimetric configuration of confluences in tropical free meandering rivers located in the Upper Amazon catchment. Since river confluences in tropical environments represent areas where biota is concentrated, a better understanding and characterization of these features has a particular importance for the Amazonian ecosystem. Confluence of meandering rivers or meander trains comprised by the main channel (M) and the tributary (T) imposes the following general changes in the planimetric configurations of these channels: [1] modulation of the morphodynamics of the M and T channels, and [2] modulation of the morphodynamics of the downstream Main channel (MT), thus varying both the predominant arc-wavelength and amplitude, and resembling either a constructive or a destructive effect in the superposition of curvature waves. A wavelet analysis of the normalized channel curvature was performed by using the continuous Morlet Wavelet function. This analysis indicates that important transient perturbations in the curvature frequency spectrum are developed when the width-ratio between the tributary width and the main channel width, β = BT/BM, is higher than 0.45. These perturbations become more dominant when β increases.