Hydropower in Brazil: Overview of Positive and Negative Environmental Aspects

Brazil is a country where the use of hydroelectric power for energy generation reaches the impressing amount of 70% in terms of electricity consumption, whereas the world average is around 16%. The current installed capacity in Brazil is approximately 114 GW, with an estimated total potential of 260 GW. The construction of reservoirs is associated with several environmental impacts, both of positive and negative nature. In the first group the most relevant are: energy production, employment generation, enhancement of water quality in the transformation from lotic to lentic ecosystems (turbidity reduction, higher water transparency, nutrients sedimentation and decreasing of eutrophication processes downstream), expansion of working posts offer during the construction of power plants; supply of reliable low cost energy to the region and substitution of diesel based thermoelectric generation by hydroelectric generation. The main impacts of negative nature are changes in water quality, people relocation, changes in the structure of the aquatic community, loss of genetic patrimony (flora and fauna), slopes destabilization and climatic alterations, including those related to the emission of greenhouse gases. In this sense several researches are currently being carried out in the country with the aim of quantifying the main emissions of CO2, CH4 and N2O. Eutrophication processes may also be developed in inundated areas, leading to the eventual presence of cyanobacteria. These organisms pose a special concern to Brazilian health authorities, since this was the first country to report human deaths caused by cyanotoxins (city of Caruaru, 1996). Another relevant aspect related with dams design is the possible creation of the so-called low flow reaches, downstream the reservoir. These river stretches should be kept with a minimum water flow (ecological flow), whose sound calculation is still subjected to some uncertainties. The paper presents a balance of the positive and negative environmental aspects of the construction and operation of hydroelectric reservoirs based on the large experience accumulated through research and consulting projects developed at Universidade Federal de Minas Gerais.