Caracterização morfotectônica e hidromorfológica da confluência dos rios Branco x Negro e adjascências – Amazônia, Brasil

Abstract

The geomorphology of the Amazon region exhibits unique characteristics, both in terms of its vast territory and the diversity of its vegetation, soils, rivers, and rocks. In the context of hydrological phenomena in the Amazon, river confluences play an important role in the development and understanding of the region, as they represent locations with diverse physical, chemical, and biological characteristics. Therefore, understanding how river confluences occur can provide valuable information about river regime behavior, tectonic influences, and potential biotic transitions. As such, this study focuses on the geomorphological characterization of the confluence between the Negro and Branco rivers and describes the hydromorphological functioning of the system using morphological, hydrodynamic, and tectonic parameters. Through altimetric, structural, and geomorphological analysis using field data, satellite imagery, and radar, it was possible to identify four main geomorphological zones, anomalous drainage patterns, alignment of knickpoints, and structural lineaments that shape the current geomorphology of the area. The study found that, due to a structural rearrangement of crustal blocks caused by tectonic movements along a NW-SE lineament on the left bank of the Negro River, the Branco River's channel shifted to the current confluence, resulting in increased sediment deposition in its estuarine region and the formation of a delta that extends into the Negro River, creating a physical-geographic barrier that reduces the width of the Negro River by up to 15 km. To maintain a constant flow, the Negro River surpasses the flow velocity of the Branco River by up to three times and increases the depth of its channel proportionally. These conditions lead to interactions between sediment deposits at the confluence that do not fit the current models, despite maintaining hydraulic interactions, as they are closely linked to the fact that the confluence of the Branco and Negro rivers is controlled by the Amazonian neotectonic regime.