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Research Document - 2012/039

Review of approaches and methods to assess Environmental Flows across Canada and internationally

By T. Linnansaari, W.A. Monk, D.J. Baird, and R.A. Curry


Freshwater resources are under increasing threat from anthropogenic activities, both in terms of consumptive and non-consumptive use. The increasing societal demands for water have led to substantial flow alterations in rivers in Canada. Flow alteration can be directly linked to impacts on the physical and chemical attributes and processes of rivers and subsequent ecological changes. In addition to increasing demand of water, the ecological, social and cultural values of rivers are increasingly being recognized. With so many competing needs for water, there is an urgent need to develop sustainable environmental flow management guidelines to manage the risk associated with alterations to the flow regime in Canadian rivers. A national environmental flow framework would also support the habitat protection provisions of the Fisheries Act (S.35).

This document is intended to serve as an input for a scientific review process at a national level and to provide background information on i) conflicting terminology used in the environmental flows literature, ii) environmental flow assessment methodological approaches and iii) current status of environmental flow guidelines used in different jurisdictions in Canada. The information contained in this document was critically discussed by an assembled group of experts who will provide further scientific advice on environmental flow regimes for the Canadian context in a separate document.

The terminology used in environmental flow assessment literature is variable; "instream flow needs" and "environmental flows" seem to be the most widely used and inclusive terminology.  The endorsement of these terms for wider use in Canadian context needs to be further verified by an assembled group of experts.

The techniques used in environmental flow regime assessment were classified into four general categories (hydrological, hydraulic rating, habitat simulation and holistic methodologies and frameworks) and the benefits and weaknesses are reviewed. The four methodological categories differ drastically in the scope and implementation costs and therefore, are suited for different level of assessment of environmental flow regimes. Most assessment methods are not based on tested relationships between the extent of flow regime alteration and ecological response. A recent trend seems to suggest that there is an increasing recognition that any environmental flow method used alone will not be sufficient for determining environmental flows in all situations; the holistic methods and frameworks (wherein a combination of other methods are used) are increasingly common especially in large scale projects.  

The examination of the current methodologies used in different jurisdictions in Canada revealed that many provinces do not have an established guideline to be used for determining environmental flow regimes. Some provinces have established guidelines to be used in uncontroversial situations (i.e. cases that are believed to lead to no harmful alteration, disruption or disturbance to fish habitat, "HADD"). None of the jurisdictions appeared to have an established environmental flow framework that is used in larger-scale projects (i.e. "potential or incurring HADD") but evaluation is carried out on a case-by-case basis.

Various options for establishing a national environmental flow regime framework are available but at least two suggestions are to be examined more closely by an assembled group of experts. The first option is related to incorporating a framework similar to the process characterized by the Ecological Limits of Hydrologic Alteration (ELOHA; Poff et al. 2010) to at least some degree in Canada. The second option is to establish a two-tiered framework wherein the more general Level 1 ("no HADD") assessment would be based on some combination of hydrologically-based guidelines to protect the natural variability in river flow regimes with some cut-off values to terminate water withdrawal during the lower flows. The more specific Level 2 ("potential HADD") assessment would be based on a holistic approach for which a detailed protocol would need to be drafted to ensure the ecological integrity, comparability and transparency across Canada. Regardless of the type of framework to be established, it is fundamental that the established environmental flow standards are preceded and followed by a controlled monitoring program and the possibility to refine the environmental flow regime standards by adaptive management in an iterative process.

The need to establish a system to categorize Canadian rivers (or their segments) into ecological management classes needs to be further discussed by an assembled group of experts. The potential benefit of such classification would be the possibility to design different environmental flow standards based on the ecological or societal "value" of various river sections. Finally, a time-frame must be determined to ensure that a national environmental flow framework will be established in an expedited manner.

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