Comprehensive Study Report

Hydro-Québec is planning to build a new hydroelectric facility at the Grand-Mère site, on the Saint-Maurice River.

The Grand-Mère hydroelectric generating station (150 MW) is becoming obsolescent and experiencing operating problems. In addition, the design flow is inadequate (5 925 m³/s), and this causes bottlenecks on the river, preventing optimization of the output from the facilities of the Saint-Maurice complex located farther downstream (Shawinigan I and II, La Gabelle).

Of the different options studied (abandonment, upgrading or construction of a new generating station), the construction of a new station is considered the most acceptable solution from an economic, social and environmental standpoint, and it is also in keeping with Hydro-Québec's strategic plan.

The new facility will be composed of many new works (220 MW plant, spillways with a capacity of 8 225 m³/s, sending-end substation, protective works) and some existing ones (generating station, left and right gravity dam). The existing power station will be preserved and its equipment dismantled; its future vocation will be determined based on the recommendations of a committee formed by the company and the community.

In winter (mid-December to mid-March), Hydro-Québec will adopt a new production schedule to have the generating station contribute to peak generation, simultaneously with the other plants located downstream. It will be equipped to quickly adjust to an operating flow of between 200 and 1 040 m³/s. This new generating mode will cause water-level fluctuations, leading to the formation of ice-push ridges and cracks along the riverbanks, which may impede use of the waterway for winter activities.

Commissioning of the new control structures will induce major hydrodynamic changes in the environment and lead to the disappearance of a smallmouth bass spawning ground (150 m²) and a sucker spawning area (1 547 m²) situated downstream from the left gravity dam, along with siltation over an area of 3 100 m² including a sucker spawning ground situated downstream from Simard Point.

An environmental assessment of the project is required under the Canadian Environmental Assessment Act (CEAA), because of the resulting loss of productive capacity of fish habitat, a situation which requires the issuance of an authorization under subsection 35(2) of the Fisheries Act.

This report fulfils the obligation of the Department of Fisheries and Oceans (DFO) as a responsible authority pursuant to the CEAA to conduct an environmental impact assessment of the project in consultation with other federal authorities with appropriate expertise.

In view of the mitigation measures and the proposed monitoring programs, along with the undertakings by the proponent, DFO has determined that the proposed project, as defined in the scope of the study, is not likely to have important adverse effects on the environment.