Análise hidrossedimentar da região de confluência dos rios Japurá e Solimões – AM

Abstract

The geomorphological complexity of the confluence between the Solimões and Japurá rivers, particularly in the Paraná do Aranapu region, presents significant challenges for accurately delineating the Japurá River mouth. This research investigated the hydrosedimentary dynamics of this confluence zone, testing the hypothesis that the channel downstream of Paraná do Aranapu constitutes, from a hydrosedimentary perspective, a secondary channel of the Solimões River system. The methodology integrated three complementary approaches: (i) analysis of MODIS imagery (2003-2024) to estimate suspended sediment concentration (SSC); (ii) in situ spectral characterization of water bodies using field spectroradiometry; and (iii) analysis of historical hydrological time series (river stages and precipitation) provided by the Brazilian National Water Agency (ANA) and TRMM satellite data. Data processing involved statistical correlations, spatial analyses, and time series construction through geographic information systems. Results demonstrated that the Solimões River exerts dominant control over the hydrosedimentary regime of the lower Japurá downstream of Paraná do Aranapu, particularly during the flood season (December to March). Spectral signatures revealed distinct patterns: while the Japurá upstream of Aranapu maintains its characteristic black water properties, the downstream reach exhibits spectral signatures analogous to those of the Solimões, with high reflectance in the 550-700 nm bands correlated with elevated SSC values. The correlation between SSC data from the Downstream Solimões and Downstream Japurá sections (R² = 0.92) corroborates this hydrosedimentary influence. The evidence obtained indicates that, from a hydrosedimentary standpoint, the effective mouth of the Japurá River is located upstream of Paraná do Aranapu, with the downstream channel functioning as an integral component of the Solimões system. This finding transcends mere cartographic considerations, highlighting the need for conceptual revision of how "river mouth" is defined in multichannel fluvial systems within Amazonian alluvial plains, where confluence zones constitute dynamic transitional spaces controlled by hydrological seasonality. This research demonstrates the potential of remote sensing integrated with field data as a fundamental tool for understanding the complex Amazonian fluvial geomorphology.