摘要：In some hydroelectric plants, downstream of the dams, there is the formation of reduced instream flow. Normally, dams structures with sills are added to increase the width of the channel and, consequently, reduce environmental impacts. This hydraulic configuration increases the liquid depth and reduces the average velocity, which causes more importance of the diffusive term in the behavior of the water quality parameters along the reduce instream flow. The focus of the study is the Capim Branco I Hydroelectric Power Plant, located in the lower course of the Araguari River, Triângulo Mineiro, which has 9 km of length and five small structures with sills. The simulations of OD, DBO, organic nitrogen, ammonia, nitrate and phosphorus parameters were performed in the AQUATOOL tool, from October 2009 to September 2010. The simulations for the diffusion coefficients E equal to 5, 10, 15 and 20 m 2 /s were compared with simulations of E equal to zero. The reduced value of E results greater influence on the behavior of water quality parameters. The pollutant load of the Marimbondo stream increased considerably the variation of BOD, phosphorus and organic nitrogen (dry and rainy period, respectively, 2% and 4% for BOD, 6% and 7% for phosphorus and 5% and 6 % for organic nitrogen). The DO variation was reduced in the dry and rainy season, remaining less than 1% in the majority of reduce instream flow. The nitrification process resulted in high ammonia variations, with a peak of 10% in the dry period and 14% in the rainy season, and a high nitrate variation, with a peak of 16% in the dry period and 18% in the rainy season. Towards the impact of E coefficient on the behavior of the parameters, it is suggested that this coefficient is previously obtained in the field by experimental methods with tracers.
关键词：Reduced Instream flow; Diffusion coefficient; Water quality.;Trecho de vazão reduzida; Coeficiente de difusão; Qualidade da água.
