Science Response 2020/035

Science Review of the Change in Timing of Impoundment for the Keeyask Generation Project

Context

The Keeyask Generation Project is a new hydropower development on the lower Nelson River in northern Manitoba. The project includes a powerhouse with seven turbine generators situated on the north side and a spillway located on the south side of Gull (Keeyask) Rapids. An Environmental Impact Statement (EIS) was prepared by the Proponent, Manitoba Hydro, and reviewed under the Canadian Environmental Assessment Agency (CEAA) in 2012–2014. The Project was approved on June 27, 2014 and construction commenced in 2016.

Within the 2012 EIS, environmental effects were assessed and approved for reservoir impoundment from an elevation of 155 m ASL (above sea level) to an elevation of 159 m ASL to commence in August 2019 and be completed by October 2019 (EIS, Section 4.6.15–Reservoir Impoundment). Since this time, construction delays have put the project behind schedule. Subsequently Manitoba Hydro has requested an amendment to change the timing of water-up to late February 2020 and timing of impoundment to late March/early April 2020, rather than the originally proposed late summer/fall schedule for both activities (August 2019–October 2019). Consequently, the under ice conditions should be considered in the assessments of water-up and impoundment in the winter rather than the original open-water environmental assessment.

The evaluation and authorization of the proposed amendment has been divided by Fisheries and Oceans Canada (DFO) Fish and Fish Habitat Protection Program (FFHPP) into two phases. The first phase is the water-up of the Keeyask Generating Station (including removal of the coffer dams and rock groyne) up to the prevailing level outside of the cofferdams (current water level ~156 m ASL). The second phase is the impoundment of the reservoir to the full supply level (FSL), at an elevation of 159 m ASL.

Based on Manitoba Hydro’s modelled prediction, the open water hydraulic zone of influence of the Keeyask reservoir at FSL of 159 m might extend upstream ~42 km from the Generating Station to about 3 km downstream of the outlet of Clark Lake, with a flooded area of approximately 45 km² (Figure 1).

This Science Response Report results from the Science Response meeting regarding the Science Review of the Change in Timing of Impoundment for the Keeyask Generation Project held on February 27, 2020, in Winnipeg, MB.

The amendment is currently under review by DFO’s FFHPP for decision. FFHPP has requested that DFO Science review the proposed amendment. In particular, the objectives of this review are to:

1. review the outputs of the hydrodynamic model presented in the amendment and identify uncertainties and data gaps;
2. identify other potential impacts that may occur with winter impoundment;
3. determine the appropriateness and adequacy of the proposed mitigation and monitoring measures, and;
4. if necessary, recommend additional information, studies, data collection that are required for DFO Science to complete its assessment.

This Science Response Report resulted from the Science Response Process of February 27, 2020 which included a review of several documents and/or presentations received from FFHPP.

Science Response 2020/035 (PDF, 1,447 KB)

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