First Essentials Toward Environmental Flows for São Francisco River (Brazil): Recovering Damaged Ecosystems and Meeting Human Needs

This paper discusses the main benefits, feasibility, and challenges of implementing environmental flows in the lower reach of São Francisco River (SFR), Brazil, in the context of river basin revitalization, based on the experiences of a developed research project. The 631,133 km2 N basin of SFR covers 7.4% of the Brazilian territory, with enormous differences in its climatic and bio-physical characteristics. Rainfall ranges from 350 to 1,900mm over its area in normal years, the mean annual "natural" flow should be 2,850 m3/s, and flows at the mouth of SFR used to be greater than or equal to 854 m3/s in 95% of the time. SRF has been fragmented by dams planned to generate electricity mostly and also for flood control, irrigation, and water supply. Although some undeniable benefits exist, considerable environmental degradation and ecological losses have resulted from damming and water abstraction. The hydrological dynamics in its lower reach were extremely altered. Artificial dikes and river embankments prevent river-floodplain interactions, resulting in significant consequences on organic matter and nutrient fluxes and reproduction of the aquatic fauna as well. Navigation is now particularly restricted. Formation and immobilization of sandbanks have been noticed. The sediment budget at its mouth is now totally unbalanced, transforming the river-ocean relationship. Traditional fishery activities have been limited by stock depletion, resulting in impoverishment of local populations with consequent social ruptures. Even after all this, inter-basin diversion works are under way to export additional flows. The SFR Basin Management Plan refers to the benefits of "artificial flooding" in its lower reach, this way expecting to recuperate some ecological functions and to improve fishery. This exposes the need of implementing "environmental flows," what still may sound as an "unnecessary luxury" to some people, because land and water use conflicts and lack of access to water still remain. However, "environmental flows" must be addressed as a vital approach, given the imperative need of pursuing sustainability in the use of natural resources, indeed resolving those mentioned problems. A multidisciplinary research team dealt with the challenge of analyzing and proposing first steps for an eco-hydrological approach for SFR. First understandings about the possibilities of prescribing environmental flows for the lower reach of SFR were delineated. However, enormous obstacles still have to be faced: (a) prescription of more ecologically based environmental flows; (b) technical issues related to hydraulic structures of the dams; (c) the strong and unbalanced influence of the hydropower sector over other stakeholders; (d) political issues concerned to water managers, including problem understanding; (e) difficulties for agreement on trade-offs and compromises among stakeholders; (f) and uncertainties about water availability to meet the requirements of environmental flows due to current and potential water uses, besides the perspectives related to climate change.