Análise qualitativa e quantitativa da histerese entre vazão e concentração de sedimentos durante eventos hidrológicos

Abstract

R ESU M OA relação entre a vazão -Q e a concentração de sedimentos em suspensão -CSS, apresenta padrões temporais complexos durante eventos de chuva governados pela geomorfologia, uso e manejo do solo e precipitação. Este fato tem implicações relevantes no entendimento e na descrição dos processos erosivos e de produção de sedimentos em bacias, padrões que podem ser avaliados pelas características da histerese entre a CSS e a Q. Neste estudo foi analisado o efeito histerese de 19 eventos de chuva-vazão em uma bacia agrícola, no sul do Brasil; os eventos foram separados em duas fases distintas em relação ao manejo do solo, com e sem a utilização de práticas de conservação de solos. O conjunto de eventos foi classificado segundo o tipo de histerese e calculado o valor de um índice de histerese (IH) para avaliar a magnitude desta defasagem. Os resultados mostram que o padrão de histerese foi de laço no sentido horário para os dois momentos, representando uma rápida mobilização e transferência de sedimentos na bacia. Em relação ao IH verificou-se que, apesar de não diferir estatisticamente entre os dois momentos, existem evidências de que as práticas de conservação de solos influenciaram sua variabilidade. Palavras-chave: bacia hidrográfica, monitoramento ambiental, hidrossedimentologiaQualitative and quantitative analysis of hysteresis between sediment concentration and flow rate during hydrologic events A B ST R A C TThe relationship between flow rate -Q and suspended sediment concentration -SSC demonstrates complex temporal patterns during hydrologic events, which are governed by geomorphology, land use, soil management and rainfall. This fact has important implications for understanding and describing erosive processes and sediment production in catchments. These patterns can be evaluated by their loop hysteresis characteristics on the graph of SSC vs. Q. In this study, the hysteresis effect was analyzed for 19 rainfall events in a rural catchment in Southern Brazil. The events were separated in two groups in relation to soil management (with and without soil management practices). The events were classified according to the type of hysteresis, and a hysteresis index (HI) was calculated to evaluate the magnitude of the difference in phase. Results show that the hysteresis pattern was a clockwise loop, indicating that the peak SSC occurred before the peak Q, which represents rapid mobilization and transfer of sediment in the catchment. The HI was not statistically different between the two periods studied, although there is evidence that the conservation practices do have some influence on the index.

Quantifying the impact of no‐till on sediment yield in southern Brazil at the hillslope and catchment scales

“…Hysteresis behaviour is commonly used to describe erosion processes at the catchment scale (Eder et al, 2010;Minella et al, 2011;Steegen et al, 2000), and it may contribute to a better understanding of sediment mobilization, transfer processes, and their control factors (Bowes, House, Hodgkinson & Leach, 2005;Duvert et al, 2010).…”

Assessment of Turbidity as a Quick Tool to Quantify the Sediment Transport

“…The turbidity values are changed according to the dissolved elements present in the water as, for example, iron (SILVA et al, 2009) and particle sizes (REGÜÉS; NADAL-ROMERO, 2013) so that there were differences between the turbidity values in relation to amounts of suspended solids. After that, there are sediment concentration changes at same flow rate according to the hysteresis behavior (MINELLA et al, 2011).…”

Use of the swat model for hydro-sedimentologic simulation in a small rural watershed

“…the daily simulations of total flow discharge were slightly higher, but the nse values show a low relation between the simulated and observed values. the main limitation of swat to represent the variables on a daily scale is related to the short, rapid rainfall events that occur in small headwater watersheds (Minella et al, 2011). these events are characterized by complex hydrographs that are highly dependent on rainfall characteristics.…”