Multitemporal analysis of the Solimões-Amazonas river system between the Purus and Negro tributaries, Western Amazon, Brazil

Abstract

The geomorphological features of some stretches of the Solimões-Amazonas river system have been studied in the past decades by means of remote sensing images combined with multitemporal analyses, which mainly highlighted the morphological changes in the system’s floodplains and channels. Early studies used cartographic databases less accurate than the current ones and did not take into account certain factors, such as the contours the river valley, sensor type, and data inaccuracy and incompleteness, thus reducing accuracy. Currently, channel migration rate and definition of the fluvial style in different river stretches, which vary amongst the most well-known types in literature, stand out among the most emphasized factors in the analysis of this river system. This work demonstrates, by means of multitemporal analysis of Landsat-5/TM images, the final stage of evolution of the Solimões-Amazonas river system, in the stretch between the Purus and Negro tributaries, from 1991 to 2011. Interpretations point out a slight predominance of depositional processes relative to the erosive ones along the analyzed stretches, covering areas of 8.56 km² and 6.86 km², thereby attaining a mean migration rate of 0.32%/year. The depositional processes are mainly concentrated on the convex part of the meanders and areas downstream of the islands, including the formation of new islands, the erosive on the concave part of the meanders and upstream the islands. Despite the erosion and deposition dynamics observed in the study areas, it was possible to ascertain a high stability pattern for the channels, which showed to be consistent with the bathymetric data and migration rate values found during regional geological studies, which helped characterize the current river style as anabranching.