Coeficiente de rugosidade de Manning para o rio Paracatu

Abstract

RESUMOPela teoria do escoamento em canais abertos, o coeficiente de rugosidade de Manning é um dos principais parâmetros para descrição da vazão sobre uma superfície. Uma das dificuldades da aplicação da equação de Manning é a definição do seu coeficiente de rugosidade em rios e canais, razão pela qual o presente estudo tem como objetivo, estimar o coeficiente de rugosidade de Manning para os períodos de vazão mínima e máxima média mensal, em alguns trechos do rio Paracatu, e propor um modelo baseado em redes neurais artificiais para estimar o coeficiente de rugosidade. O coeficiente foi determinado em função das características geométricas do canal (área molhada, raio hidráulico e declividade do canal) e das séries de vazão de seis postos fluviométricos do rio Paracatu. Utilizaram-se séries de vazão de 21 anos . O coeficiente de rugosidade não apresenta tendência (maior ou menor) em função apenas do período seco ou de cheia. As características da margem e do leito do rio influenciam diretamente nos valores de coeficiente de rugosidade. O modelo baseado em rede neural apresentou desempenho satisfatório, o que possibilita estimar o coeficiente de rugosidade em função da cota, vazão, declividade e do raio hidráulico do rio. Palavras-chave: vazão, condutos livres, redes neurais artificiaisManning roughness coefficient for Paracatu river, Brazil ABSTRACTAccording to open channel draining theory, the Manning's roughness coefficient is one of most important parameters to describe surface flow. One of the difficulties in applications of Manning's equation is the definition of its roughness coefficient in rivers and channels. Thus, the aims of this paper are to estimate the Manning's roughness coefficient for the periods of minimum and maximum mean monthly flow in some parts of Paracatu river and to propose a model based on artificial neural networks to estimate the roughness coefficient. The coefficient was determined in function of channel geometrical characteristics (wetted area, hydraulic radius and slope of the channel) and of the outflow series of six fluviometric stations of Paracatu river. Long-term series of 21 years (1976 -1996) of outflow were used. The roughness coefficient does not show any tendency (up or down)as a function of the dry or overflow periods only. The characteristics of margin and watercourse of river influenced directly the roughness coefficient data. The model based on neural network showed satisfactory performance, which allow us to estimate the roughness coefficient as a function of the quota, slope and hydraulic radius of the river.

Manning’s roughness coefficient for the Doce River

“…It is observed, then, that the methodology used in this study presented results compatible with the studies that used HEC-RAS to calibrate "n". Figure 4 shows that, for the same river flow station, the variation of "n" occurs over time, which was also observed by Lyra et al (2010) for the Paracatu River, and these authors showed that the roughness coefficients varied significantly among the seasons. Some stations, such as Belo Oriente (C), presented large deviations from the values, whereas in Colatina (G) all values found are close to the median.…”

“…For example, for station 56425000, of the 19 cross-sections analyzed, it is found that by varying "y" and calculating "n", in 17 profiles the relation between these variables was directly proportional, while in two it was inversely proportional . It can be observed that for most stations there is not only one behavior, that is, in some sections the relation between these variables was directly proportional throughout the year, corroborating with Lyra et al (2010), while in others it was inversely proportional, as observed by Zink and Jennings (2014), Fathi and Drikvandi (2012), Matos et al (2011), Kim et al (2010) and Chow (1959). There were also sections where it was not possible to observe any correlation between the two variables.…”

“…As done in Lyra et al (2010) and Golshan, Jahanshahi and Afzali (2016), the slope of the water line was considered approximate to the slope "I" of the bottom of the river. According to CBH-DOCE (2005), the approximate mean slopes of the main channel of the river are 0.00075 m/m at the high, 0.00059 m/m at the medium and 0.00026 m/m at the low Doce.…”

“…Matos et al (2011) based their research on theoretical and practical studies to determine the roughness coefficient of the Sapucaí River in Minas Gerais. Lyra et al (2010) determined the roughness coefficient for the Paracatu River as a function of the geometric characteristics of the channel and the series of daily flow rates from river stations existing along the river.…”

Modelagem hidrológica da bacia hidrográfica do Rio Macaé utilizando o MOHID Land

“…Tanto a permeabilidade do terreno quanto as características da vegetação foram ajustadas através do coeficiente de rugosidade de Manning, aplicados tanto para o solo quanto para a vegetação. De acordo com a teoria do escoamento em canais abertos, o coeficiente de rugosidade de Manning é um dos principais parâmetros para descrição da vazão sobre uma superfície (LYRA et al, 2010).…”