Morfodinâmica e hidro-geomorfologia do médio rio Araguaia: investigação dos padrões e dos controles físicos e sua relevância para a análise ambiental
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2023-08-25
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Universidade Federal de Goiás
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The Araguaia River represents the last and most important free-flowing river located in the Cerrado-Amazon ecotone. The increasing human influence on this river system poses an imminent threat to the valuable ecosystem services it provides. Therefore, it is essential to produce knowledge about the physical structure and functioning of this river, which serves as a basis for a significant portion of the biome's biodiversity. This thesis contributes to the fields of Geomorphology and Hydrology of large tropical rivers, bringing new discoveries that enrich the existing body of research on the Araguaia system. In the first paper, we conducted an assessment of the planform morphology changes in the upper-middle course between 2001 and 2018, expanding the temporal data series on the evolution of macroforms to a 53-year period. We found that the current transition phase of the river, characterized by the contraction of the channel's active zone and the partial loss of braiding due to a higher representativeness of the islands, is likely related to changes in the hydro-sedimentary regime over the last two decades.
Based on a set of channel and floodplain geomorphological variables, in the second paper we developed a methodology to subdivide the middle Araguaia into 19 distinct reaches (R1-R19), which were further clustered into five major segments (SI-SV). We found that changes in valley gradient have a significant influence on the morphology of SI, SIII, and SIV, while the inflow of important tributaries and the nature of the valley floor are the main controlling factors for the fluvial style in SII and SV, respectively. This large-scale planimetric characterization of the river's middle course complements previous geomorphic studies, providing insights into the morphological diversity and sensitivity of each segment to environmental changes. In the third paper, we present a new approach to the existing classifications in the literature of flood events in the middle Araguaia. Small-scale floods (types B and D2) exhibit distinct attenuation patterns associated with the occurrence of drier years (D2). The attenuation of intermediate-scale floods (types C and D1) and large-scale floods (type A) is influenced by the magnitude of maximum flows at the upstream river gauge station, with no statistical significance for the influence of tributaries on peak changes. Flood hydrograph properties were found to respond to the regional geomorphological organization of the system. When considering the segments proposed in the second paper, we observed that the nature of the valley floor plays a central role in the efficient transport of floods in SI, SIV, and SV. The wide and complex floodplain in SII significantly influences the storage capacity, allowing for gradual dissipation of floodwater excess and peak attenuation. Water diversion to the old system (Rio Javaés) exhibited unique transfer patterns under different flow conditions, resulting in overall annual losses and gains in SIII. The methodologies and disciplinary knowledge produced in this thesis can support future interdisciplinary work and investigations in the context of environmental sciences.
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SUIZU, T. M. Morfodinâmica e hidro-geomorfologia do médio rio Araguaia: investigação dos padrões e dos controles físicos e sua relevância para a análise ambiental. 2023. 109 f. Tese (Doutorado em Ciências Ambientais) - Pró-Reitoria de Pós-graduação, Universidade Federal de Goiás, Goiânia, 2023.