Hydromorphodynamic interactions in the Sepotuba river basin - Upper Paraguay, state of Mato Grosso, Brazil

Author(s)

Gustavo Roberto dos Santos Leandro

• Document type: Doctoral Thesis
• Press: Presidente Prudente. 2020-12-10.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências e Tecnologia. Presidente Prudente
• Defense date: 2020-10-13
• Advisor: Paulo Cesar Rocha

Abstract

River basins are physical-environmental systems considered complex by virtue of the dynamics and processes that occur in their compartments. In this regard, this doctoral dissertation aims to investigate hydromorphodynamic interactions taking place at different spatiotemporal scales in the hydrographic basin of the Sepotuba river, Upper Paraguay, state of Mato Grosso, Brazil, and to analyze the morphological evolution of the river-floodplain system in its lower reaches. In terms of methodological procedures, the study drew on a theoretical review; a cartographic survey (using topographic maps, satellite images, thematic maps, geoprocessing software); secondary data acquisition and analysis; monitoring of hydrodynamic and sedimentary variables; and laboratory and statistical analysis. The integration between the inter-annual behavior of rainfall and the progressive advance of monocultures and livestock contributed to the occurrence of hydrological periods, namely: from 1970 to 1985, from 1986 to 2000, and from 2001 to 2018. Initially, in the first hydrological period, the river flow progressively increased in response to the rainfall dynamics. However, in the second half of the 1980s, a new basin-related variable started to affect the river flow behavior. In this context, the transition to the second hydrological period was marked by an increase in the rainfall standard deviation – the highest rate in the entire time series – and by an increase in the average flow. The third hydrological period was marked by fluctuations in the river's flow rates and progressive decreases thereof as compared to the previous period. In terms of seasonality, the greatest floods (January-April) occurred in the second hydrological period; and a greater number of irregularities were observed in the channel flow between the first and last periods. From the seasonal 2017-2018 timeframe onwards, bottom sediment granulometry showed the same temporal pattern. However, spatial changes were observed with regard to geomorphological compartments. In this sense, the current hydrodynamics prompted by the flow decrease in the last hydrological period and the increasing sediment inputs to the river basin have contributed to the formation of channel deposits. Additionally, the dynamics underlying bottom and suspended sediments, coupled with the water flow behavior, may provide indicators of environmental degradation. This was because there were variations and peaks in the seasonal suspended sediment discharges, predominantly in the flood period, in the confluence of the Sepotuba river and the Paraguay river. Finally, the study concluded that, between the first and second hydrological periods, the energy input in the river-floodplain system, resulting from the rainfall and land-use interaction, contributed to the morphological changes observed in the system, which took place through mechanisms of meandering, migration and avulsion. Conversely, the third hydrological period showed that land uses have compromised water availability in the system, as evinced by the current sedimentary aspects and depositional processes in the river channel such as sediment transport, point bars, convex banks, levees, and void filling. (AU)

• FAPESP's process: 16/07635-0 - HYDROMORPHODYNAMIC INTERACTIONS IN THE SEPOTUBA RIVER - HIGH PARAGUAY RIVER, MATO GROSSO - BRAZIL
• Grantee: Gustavo Roberto dos Santos Leandro
• Support Opportunities: Scholarships in Brazil - Doctorate