Relações entre precipitação, escoamento e sedimentos suspensos na bacia do Rio das Antas, Goiás
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2017-09-06
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Universidade Federal de Goiás
Resumo
Sediments transported by surface runoff and by rivers are essential components in the
comprehension of changes in a river basin and the quality of aquatic systems. The high variability
of rainfall events, the SSC and the relation between them produce complex behavioral dynamics
difficult to interpret but the study of these aspects is a useful and frequently used tool in the
quantification of impacts due to erosive and hydrossedimentological processes. The main objective
of this study was to characterize and quantify the hydrological, sedimentological and granulometric
characteristics of the urban watercourse of the Rio das Antas basin, located in Anápolis, Goiás,
wich faces various erosion processes. Continuous monitoring of precipitation, flow rates, sediment
concentrations and turbidity was performed using pluviographs, linigraphs, an automatic sampler
and a laser granulometer during most of a rainy season, where samples were collected and 14
events were analyzed. Descriptive statistical analyzes, identification of hysteresis patterns, Event
Mean Concentration, “first flush” phenomenon effects and grain size distribution and their
relationships with precipitations and flow rates were performed. The peak concentration of total
sediments reached 3,380 mg L -1 , and approximately 83% were suspended sediments. No “first
flush" has been recorded in any event. The highest mean concentration observed for suspended
sediments was 1,714.6 mg/m3 and the mean of the events was 1,001.3 mg/m3, values considered to
be high when compared to river basin flows, where the highest was 15.49 m 3 s -1 . The maximum
flow rates were determinant in the total sediment, however, the same flow range carried very
different amounts of suspended sediments during the floods. This behavior suggests that the
variation also depends on precipitation characteristics and sediment sources. In the hysteresis
analyzes, it can be verified that these sources are located farther from the monitoring point, but are
also the river itself, since the most frequent hysteresis loop was "Figure Eight" followed by the"Counter Clock-wise” type. There were complex hysteretic loops characterized by multiple peaks
of flow and sediments. The size of particles carried by the flow varies throughout the rainy season.
The suspended sediment particles had dimensions between 0.0019 mm and 0.990 mm being
characterized as sandy silt material. The small and medium particles were more frequent in final
events and larger particles occurred in the middle of the period. Finner particles were more present
during the rise of the hydrograph and in the recession phase the amount of particles with
dimensions between 0.2 mm e 0.6 mm increased in some events. Particles larger than 0.6 mm were
not related to precipitation. It was also observed that the amount of dissolved solids decreases with
increasing particle size and may indicate that larger particles have less capacity to absorb/adsorb
other pollutants. It is observed that the suspended sediments vary between the events and within
the same event and depends on the hydrological behavior, the characteristics of the water body and
the type of monitoring.
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DIDONET, Thais Teodoro dos Santos Cordeiro. Relações entre precipitação, escoamento e sedimentos suspensos na bacia do Rio das Antas, Goiás. 2017. 101 f. Dissertação (Mestrado em Engenharia Ambiental e Sanitária) - Universidade Federal de Goiás, Goiânia, 2017.