Morfologia e hidrosedimentologia da Barra Três Ilhas no alto Rio Paraná, município de Querência do Norte, Paraná

Abstract

The Upper Paraná River channel, between the Porto Primavera Dam and Itaipu backwater, presents a multichannel pattern of up to seven secondary channels in sections of 12.5 km width, and nodal points of 1.2 km. The width and number of secondary channels reach are related to the magnitude and number of islands. The avulsive islands, although in smaller numbers (only 5), are the largest morphology in the reach, while the intra-channel islands (more than two hundred) are the more frequent element in the channel. The study reach also presents stable and mobile sand bars according to the local hydraulics. The formation of intra-channel islands begins with the stabilization of the sand bars, which, depending on the exposure time and the hydrological regime, can aggrade by mud sedimentation and vegetal development. Our study focuses on the understanding of intra-channel processes active in the formation and evolution of the Três Ilhas Bar in the Upper Paraná River. To achieve this goal we obtained the hydraulic, morphometric, and grain-size parameters through ADCP and echo sounder plus suspended and bottom sediment sampling, and a multitemporal analysis of satellite images. The Três Ilhas Bar, localized upstream to the Três Ilhas Archipelago, comprises an area of 0.14 km2 and is partially vegetated. It has been stabilized for fifteen years. The bar divides the river into two asymmetric channels (main and secondary channels) concerning depth, width, and flow characteristics. The bar divides the river into two asymmetric channels (main and secondary channels) concerning depth, width, and flow characteristics. The low suspended sediments concentration in the secondary channel and the finner texture of the deposits around the bar and secondary channel indicate constancy in the deposition processes of these locals. Main channel bed sediments are predominantly composed of medium and coarse sand. The bar sedimentary profile is predominantly formed of cross-bedding fine and medium sand. The flow regulation by the Porto Primavera Dam (30 km upstream the bar) since 1999, reduced the peaks of maximum flow, creating a favorable condition for the stability and evolution of sandy deposits in the channel, including the Três Ilhas Bar. The results indicate that the processes evolution and position of the bar, upstream of the Três Ilhas archipelago, are part of the process formation of the fourth island of the archipelago. Studies of this nature are important to understand the conservation and environmental management, not only for the Upper Paraná River region but also for future exploration projects.