Science Advisory Report 2010/055

Science Evaluation of Instream Flow Needs (IFN) for the Lower Athabasca River

Summary

  • The Lower Athabasca River is most sensitive to water withdrawals during low flow conditions (both within and across years). Low flow conditions occur mainly during the winter season but can also occur at other times during years of low precipitation.
  • While the models used within the various P2FC technical reports are generally acceptable, they are based on a large number of assumptions that cannot be validated with the presently available data on fish biology and habitat for the Lower Athabasca River. Thus, one of the principal recommendations of this scientific review is that the predictions of the various models should be field tested.
  • Tributaries to the Lower Athabasca River were not within the scope of the P2FC technical analyses. While the tributaries do not constitute a large spatial area relative to the overall drainage basin and thus likely contribute relatively little to the overall flow of the Athabasca River, they likely provide important spawning and rearing habitat necessary to sustain the fish populations in the Lower Athabasca River. Thus, there is uncertainty resulting from considering the mainstem of the Lower Athabasca River in isolation from its tributaries.
  • Following the conclusion of this scientific review, a recurrent error within the climate change analysis and the main P2FC report was reported. The result of this error i.that th.General Circulation Model (GCM.projection.for change.in minimu.(winter.flows are often greater than what was reviewed, and changes in mean (summer) flows are often smaller than what was reviewed. It is recommended that the climate change analysis, and any other technical analyses using these climate change projections, be re-conducted to address this error.
  • There are multiple assumptions for individual evaluation criteria (EC), and potentially compounded error both within and among the various ECs. This may lead to an overall directional bias across the various EC reports..As such, a precautionary approach to water withdrawals is recommended.
  • Although uncertainty exists around what constitutes an ecosystem base flow (EBF), there was concurrence that a flow should be established for the Lower Athabasca River below which there would be no water withdrawal. Participants agreed that this flow should be established using a precautionary approach, and should consider the assumptions, uncertainties and measurement error across ECs (discussed herein).
  • Despite the limitations in the biological information (along with the stated uncertainties), the information and models reviewed are the best currently available, and can thus be used to provide guidance regarding potential effects of water withdrawals to the ecosystem.
  • From a hydrologic perspective, the Option H water withdrawal schedule (the non-consensus recommendation in the P2FC report) was found to be proportionally small relative to historic flow conditions during most times of the year, in most years, in the Lower Athabasca River. Given this information, it is unlikely that the hydrologic character of the river would be changed under the proposed water withdrawals. However, it is difficult to account for the uncertainty associated with climate change scenarios and their potential effects on the amount of water available in the river.
  • The various technical reports examine the potential effects of various water withdrawal scenarios under different flow regimes to fish habitat in the Lower Athabasca River. Given the available information, it is impossible to assess the precise extent of potential losses to fish habitat. However, these EC reports identify the potential for loss of fish habitat under certain low flow conditions, and that these habitat losses would likely be detected in a well designed monitoring program. It is a reasonable assumption that these fish habitat losses would result in a loss of productive capacity in the Lower Athabasca River.
  • Given these conclusions, participants suggested some potential habitat compensation projects. Any discussion of proposed compensation measures should consider habitat quality. Within this report, several potential compensation measures are presented for the consideration of project proponents and habitat managers.
  • A monitoring and adaptive management program is essential given the various data deficiencies within the Lower Athabasca River (information on life-history, distribution, population size of different fish species, etc.). It should be recognized that adaptive management would still be subject to the uncertainty inherent throughout the assessment of IFN for the Lower Athabasca River. A well designed monitoring program would address both the need for ongoing monitoring data and important data gaps identified within this report. .
  • A DFO Science advisory process is recommended to provide a consistent national framework for the evaluation of instream flow needs (IFN). This advisory process should focus on ecosystem indicators of IFN and include a consideration of potential climate change effects on instream flows.

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