A perspective on e-flows at hydroelectric projects in Canada

Abstract

Setting e-flows (instream, environmental or ecological flow regimes) for existing or new hydroelectric and other projects is a key worldwide consideration. A Canadian perspective and experience in arriving at e-flow regimes for ice-free or ice-covered rivers, with emphasis on small and large hydroelectric projects, is presented through general concepts and modeling approaches. Rather than a single standard approach, several methodologies are used throughout Canada, although in some regions preferred techniques may be favoured. Methods range from relatively simple desktop calculations based primarily on hydrological data to sophisticated hydrodynamic and habitat modeling followed by time series analyses. Method complexity usually depends on impact severity, particularly on fish and fish habitat. Multi-jurisdictional, legislative, climatic (e.g. ice regimes) and geographic landscapes present unique challenges for methods, data availability, and tools used to set e-flow regimes. Nature-mimicking approaches are also employed to enhance the ecological integrity of estimated flow regimes by imitating key elements of natural hydrographs and geomorphic features. More holistic approaches and scientific reviews may supplement studies, particularly when complex technical and societal issues are involved. Plans for new or modified hydroelectric projects strive to balance power generation with social and economic considerations, as well as river flow regimes for ecological needs, including fish and fish habitat.