Downstream effects
Site C will have small effects on the Peace River flows downstream of the dam.
Water flows and levels
The Peace Canyon dam, located 85 kilometres upstream of Site C, normally discharges water within the operating range of 283 to 1,982 m3/second.
The Site C dam, with additional flow from local tributaries, will normally discharge water at a rate of 390 to 2,700 m3/second. Occasionally, Site C will need to discharge additional water from its spillways.
Downstream water levels will vary, depending on discharges from Site C, flow in downstream tributaries, and topographic features at different locations on the Peace River.
Water temperatures
Water temperatures in the Peace River immediately downstream of Site C will be slightly warmer than existing conditions between July and January, with differences ranging between 0.3°C (July) and 1.5°C (January).
During the rest of the year, water temperatures in the Peace River just downstream of the Site C dam will be cooler than existing conditions, ranging between 0.4°C (March) and 0.9°C (June).
Water clarity
Downstream Peace River suspended sediments are expected to lessen. This would result in only small changes to the overall river, due to the large sediments coming from downstream tributaries.
Increased suspended sediment levels are expected to last several months from the start of reservoir filling as water picks up the sediment from previously dry land. During this time, we will monitor Peace River suspended sediment levels.
Fish habitat and methylmercury levels
Overall, we predict an increase in fish population, mainly due to an increase in mountain whitefish. We expect several other species to remain and potentially expand further into Alberta after the Site C dam is built.
To address the risk of fish stranding, we’re enhancing downstream fish habitat to provide permanently wetted protected channels for fish spawning and rearing.
The process of converting inorganic mercury to methylmercury will temporarily speed up when the reservoir is filled, due to rapid decomposition of soil and vegetation on previously dry land.