Avaliação de metodologias de regionalização de vazões mínimas de referência para bacia hidrográfica do Rio São Francisco, a montante do Reservatório de Três Marias

• Autor(a) principal: Lemos, Alysson Feliciano
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/3615
• topic: Vazões mínimas; Outorga; Gestão de recursos hídricos; Minimum flow; Water resources management; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::ENGENHARIA DE AGUA E SOLO

This work evaluates three methods measuring the minimum reference flow rates (Q7, 10 for quarterly and annually periods, Q90 and Q95) for the basin hydrological of the São Francisco River, upstream of the Três Marias Reservoir. The three compared methods are: The Traditional model, proposed by ELETROBRÁS (1985a); CHAVES et al. (2002) and depicts a specific flow rate. The Physical and Geographical Model, whose characteristics used in the regionalization context by the traditional method were the drainage area, the length of the main river, the drainage s density, the medium steepness of the basin and of the main river extracted from a hydrological consistent digital elevation model (HCDEM) which also considers the climatic characteristics such as the total annual and half-yearly precipitation, as well as the total amount found in the driest quarter; and The Probability Model on the Distribution of Extreme Events tested for the series of minimum flow rates such as Log-normal to two and three parameters, Pearson III, Log-Pearson III and Weibull. After identifying the best probability model to find flow rates, data were obtained for each fluviometric gaging stations, considering the minimum flow rates within seven days of duration associated with a 10 year return period (Q7, 10) for quarterly and annually periods observed in a calendar year. The values of the flow rates stand were associated to 90% (Q90) and 95% (Q95) during the time they were obtained from the values of the daily curve of permanence for each fluviometric gaging station. As for the regionalization method using CHAVES et al. (2002) and a specific flow rate consideration, it was necessary to identify four possible situations: 1) point of interest located upstream from a known flow rate position, 2) point of interest located between two places with known flow rates, 3) point of interest located downstream a known flow rate position and, 4) point of interest placed in a flowing channel whose mouth is located between two put fluviometric gaging stations in a channel of superior order. Either in the methodology proposed by CHAVES et al. (2002) or in the one of specific flow rates, the flow rates values were estimated from the application of specific equations for each and every situation mentioned above. After the observing the minimum flow rates of the region, comparison of the results followed for the CHAVES et al. (2002) method and the specific flow rates with the values observed for each fluviometric gaging stations. As for the traditional method, the comparison of results obtained in the present work regards the period from 1978 to 2002 as found in the Digital Atlas of the Waters of Minas (ATLAS, 2005) and has a period base dated from 1970 to 2002. The accuracy on the methods was evaluated by the application of two indexes: The relative error average and the Nash and Sutcliffe s efficiency coefficient. The results indicated that the probability Log-normal models to two and three parameters, and Pearson III, were the ones that best described the minimum flow rate data within seven days of duration, if one considers annual and quarterly periods for the three identified homogeneous areas. The areas were: the drainage area, which was the most expressive variable concerning the figures for the references of minimum flow rates in the traditional method, and for Q7,10 the drainage density and the precipitation of the driest quarter were also used. The relative errors average and the coefficients of efficiency of Nash and Sutcliffe for the traditional methodologies, CHAVES et al (2002) and specific flow rate, considering annual Q7,10, were of 26,8%, 100,7% and 94,3% and 0,81, 0,94 and 0,93, respectively. The reference of minimum flow rates based on quarterly periods provided considerable increase in water availability during the first and second quarters when compared to those obtained annually. The results then allowed reaching a conclusion: The digital model of elevation São Francisco basin hydrological, upstream the Três Marias Reservoir is hydrologically consistent. It allows an automatic determination of physical characteristics of the basin; the drainage area, the drainage density and the precipitation of the driest quarter were the variables that best represented Q7,10 in the regionalization for the traditional method; the drainage area was the most expressive variable representing Q90 and Q95 in the regionalization for the traditional method. The interpolation and extrapolation methods based on systems of geographical information and specific flow rate did not present satisfactory results in situations in which the difference observed in the area of drainage of a known flow rate place compared to another was significant; the best method of regionalization for reference of minimum flow rates for the studied basin was the traditional one, based on the use of regional regression equations; last but not least, the rate of reference for minimum flow rates based on quarterly periods provided considerable increase in the hydrical availability, making it more flexible as well as granting a better use for water in the rainiest periods of the year.