Environmental impacts of Brazil's Tucurui Dam: Unlearned lessons for hydroelectric development in Amazonia

Brazil's Tucurui Dam provides valuable lessons for improving decision-makin g on major public works in Amazonia and elsewhere. Together with social imp acts, which were reviewed in a companion paper, the project's environmental costs are substantial. Monetary costs include costs of construction and ma intenance and opportunity costs of natural resources (such as timber) and o f the money invested by the Brazilian government. Environmental costs inclu de forest loss, leading to both loss of natural ecosystems and to greenhous e gas emissions. Aquatic ecosystems are heavily affected by the blockage of fish migration and by creation of anoxic environments. Decay of vegetation left in the reservoir creates anoxic water that can corrode turbines, as w ell as producing methane and providing conditions for methylation of mercur y. Defoliants were considered for removing forest in the submergence area b ut plans were aborted amid a public controversy. Another controversy surrou nded impacts of defoliants used to prevent regrowth along the transmission line. Mitigation measures included archaeological and faunal salvage and cr eation of a "gene bank" on an island in the reservoir. Decision-making in t he case of Tucurui was virtually uninfluenced by environmental studies, whi ch were done concurrently with construction. The dam predates Brazil's 1986 requirement of an Environmental Impact Assessment. Despite limitations, re search results provide valuable information for future darns. Extensive pub lic-relations use of the research effort and of mitigation measures such as faunal salvage were evident. Decision-making was closely linked to the inf luence of construction firms, the military, and foreign financial interests in both the construction project and the use of the resulting electrical F ewer (most of which is used for aluminum smelting). Social and environmenta l costs received virtually no consideration when decisions were made, an ou tcome facilitated by a curtain of secrecy surrounding many aspects of the p roject. Despite improvements in Brazil's system of environmental impact ass essment since the Tucurui reservoir was filled in 1984, many essential feat ures of the decision-making system remain unchanged.