The number of small dams is growing around the world. Especially in Amazon, there was a five-fold increase in the number of this type of project in the last 20 years. The main drivers behind this boom are economic incentives for renewable energy, saturation of hydropower exploitation capacity in large rivers, allied with the perception that small dams have fewer negative environmental impacts than the large hydroelectric plants and consequently, fast approval and simpler social and environmental impact assessment.
In the Brazilian Amazon, the social, environmental and economic costs of large hydropower projects in the Madeira (Santo Antônio and Jirau dams) and Xingu (Belo Monte dam) rivers forced the temporary suspension of the construction of 7 new large dams in the Tapajós basin. However, an increased number of small dams has been implemented there are others planned for the Tapajós, often associated with other activities such as mining, power lines, agriculture and roads. The current Brazilian policy instruments for Environmental Impact Assessment fail to properly address the cumulative impacts of these projects, as evidenced by a recent publication in Energy Policy.
A group of researchers from the Amazon Dams Network (University of Florida, University of São Paulo and Federal University of São Paulo) analyzed the Environmental Impact Statements developed for small dams projects in Cupari sub-basin in the Tapajós watershed. They found that cumulative impacts of 28 small dams and one large hydropower project were not adequately considered in the analyzed studies. The development of one project for every 42 km of river potentially result in effects that interact with each other and with the environment, resulting in cumulative impacts. Cumulative environmental impacts (or effects) are defined as changes to the environment caused by an action in combination with other past, present and reasonably foreseeable future actions, resulting from different process of accumulation, which may be additive (sum of individual effects) or synergistic (when combined effects are greater than the sum of individual ones). Examples of neglected impacts include the alteration of hydrological conditions and dynamics, loss of fish habitats, alteration in fishing activities and riverine communities downstream. The sum of these impacts can be larger than those resulted by large dams, evidencing that small dams do not necessarily mean lower socio-environmental impacts.
The authors argue that improving the process of Cumulative Impact Assessment in the existing instruments are urgent for effective hydropower planning in the Amazon. For this, the authors state the Integrated Environmental Assessment (Avaliação Ambiental Integrada, AAI), should consider the full development scenario, including all inventoried small and large dams, and the Environmental Impact Statements demand detailed guidelines in order to better explore the potential interactions among impacts. Additionally, the researchers propose the Strategic Environmental Assessment as an instrument that can potentially contribute to better integration with other plans, programs, and initiatives at the watershed level. Although this instrument is not required by law in Brazil, it has been developed for some projects in the oil and gas sector, transportation infrastructure, as well as tourism.
International guides and a considerable number of case studies are available to improve Cumulative Impact Assessment practice at the regional and project levels. A multiscale approach is needed to address the complexity of cumulative impacts at the watershed level, as well as strengthening governance structure, public participation and articulation with civil society, universities, private sector and governmental agencies are fundamental to inform planning and management of small dams in the Amazon basin.
Athayde, S.; Duarte, C. G.; Gallardo, A. L. C. F.; Moretto, E. M.; Sangoi, L. A.; Dibo, A. P. A.; Siqueira-Gay, J.; Sánchez, L. E. 2019. Improving policies and instruments to address cumulative impacts of small hydropower in the Amazon. Energy Policy 132: 265-271. DOI: https://doi.org/10.1016/j.enpol.2019.05.003