The spectrum of rivers in the Amazon Basin

Abstract:

The Amazon River Basin is known as the host of an ecological system with one of the highest biodiversity in the world. The diversity is also found in river features: the Amazonian rivers show high degree of variation in size, and channel, depositional and erosional patterns. This study aims to understand: 1) geomorphological characteristics of the rivers, 2) their spatial distribution and 3) inter-connectivity of these characteristics. To achieve these objectives, the rivers are first digitized and characterized using Landsat images and existing remote sensing techniques. The Andean part of the basin is excluded, and a total of approximately 1000 river reaches with width ranging from 60 to 5000 m have been digitized. The rivers are characterized in terms of i) main channel width, ii) number of channels, iii) area of in-channel islands, iv) centerline sinuosity and v) meander wavelength. The results indicate that smaller reaches tend to develop single-thread meandering channels, while larger ones develop multi-thread braided or anabranching channels. The first glance of the spatial distribution of the results at the basin scale reveals that a) smaller rivers in the Andean forelands (AF) and part of the Central lowlands (CL) adjacent to the AF where sediment is sourced directly from the Andes, form high degree of meandering patterns, b) smaller rivers in the Guiana and Brazilian shields (GBS) form relatively straight patterns, and c) larger rivers in the GBS present more channels than larger rivers in the AF and the CL. A closer view at sub-basin scale shows that the channels are less confined in the AF and the CL, while they are highly confined in the GBS, although meandering structures are still found in such settings. Moreover, the connection of the rivers is studied by characterizing the confluences with attributes of their upstream and downstream channels. Such characterization also allows the assessment of the spatial variation of the channel characteristics as well as the effect of a tributary on the morphology of the main channel. Understanding the spatial distribution of the channel characteristics and geomorphological connectivity in the Amazon Basin is crucial in assessing cumulative effects of infrastructures.