ABSTRACT
RESUMO O sedimento encontrado na seção transversal de rios ou reservatórios é resultado das interações ocorridas em uma bacia hidrográfica, sejam elas decorrentes de fatores naturais ou antrópicos. Apesar da quantidade de sedimentos no rio ser o resultado dos processos que acontecem dentro da bacia, os métodos de estimativa de sedimentos baseados nessas características, ou seja, métodos determinísticos, apresentam grandes variações devido ao grande número de variáveis interferentes. Aqui foi aplicada a teoria da entropia, método não determinístico, para estimar o perfil da concentração de sedimentos a montante, a jusante e no interior de um reservatório, propondo a relação entre dois parâmetros com a finalidade de facilitar a estimativa. Foi verificado que é possível utilizar a teoria da entropia para simular o perfil de concentração de sedimentos em reservatórios. A utilização da relação entre os parâmetros facilita os cálculos, reduz o número de parâmetros modelados e, consequentemente, o tempo computacional, além de representar melhor as variações da concentração de sedimentos ao longo do perfil.
ABSTRACT The sediment found in the cross section of a river or a reservoir is the result of interactions that occur in a watershed, whether from natural or anthropogenic factors. There are still changes in the riverbed conditions depending on the type of sediment, flow velocity, changes in slope and human interventions such as hydraulic works. Although the amount of sediment in the river is the result of processes that occur within the basin, the estimation methods of sediment based on these characteristics, that is, deterministic methods, vary widely due to the large number of interfering variables. This paper deals with the application of the entropy theory, a non-deterministic method to estimate the profile of sediment concentration upstream, downstream and within a reservoir. A relationship between two parameters in order to facilitate the estimation was proposed. It can be observed that it is possible to apply entropy theory to simulate the sediment concentration profile in reservoirs. The use of the relationship between parameters facilitates calculations, reduces the number of modeled parameters and consequently the computational effort and better represents the variation of sediment concentration along the profile.
ABSTRACT
Soil particles eroded from the land surface and transported into rivers by runoff are considered one of the main components of non-point source pollution in urban watersheds. These particles also serve as a vector for a wide variety of both organic and inorganic constituents. As a result, the identification of sediment sources in an urban watershed is necessary not only to understand erosion dynamics, but also to help implement more effective measures to control and/or remediate non-point source pollution. The present study employs sediment 'fingerprinting' to determine the main sediment sources in a small residential urban watershed (0.83 km2) on the outskirts of Porto Alegre in southern Brazil. Based on an evaluation spanning 12 rainfall events, the results show that paved and unpaved roads and the stream channel itself contribute, on average, 46%, 23%, and 31%, respectively, to the suspended sediment flux in the watershed. Furthermore, the source contributions varied both between events and over the course of a single event. This appears to imply that source contributions, at least to some extent, depend on local precipitation patterns. The results from this study indicate that the level of uncertainty in source ascription tends to decline with increasing numbers of tracers; hence, successful sediment fingerprinting and source ascription in complex hydrologic environments, such as urban watersheds, may require the use of a large number of chemical and/or physical tracers.
