Headworks and surge tower upgrade (tunnel project)
We're planning to complete seismic upgrades to the tunnel system between the Alouette Lake Reservoir and the Stave Lake Reservoir.
What's new
We're considering feedback from Indigenous Nations, regulators and stakeholders about the three potential reservoir management options. We expect to identify a preferred option and begin further assessment in spring 2023.
Pre-construction site preparation for the First Set of Works started in March 2023. The main civil works contractor, Pomerleau Inc, is expected to prepare for construction in April, and start construction immediately after. The First Set of Works includes:
- Seismically upgrading the surge tower structure and concrete lining of the surge shaft,
- Stabilizing slopes,
- Constructing rockfall protection near the surge tower, and
- Installing new communications, control equipment and auxiliary power supply for the adit gate.
What we're planning
We're planning to complete seismic upgrades to the tunnel system between the Alouette Lake Reservoir and the Stave Lake Reservoir. The current tunnel system was built in the late 1920s and doesn't meet today's seismic standards. We'll be upgrading the tunnel system to ensure this important infrastructure can withstand and remain operable following a major (one in 10,000-year) earthquake.
Schedule
To provide time to complete consultation and engagement activities with Indigenous Nations, regulators and stakeholders on reservoir management and its potential impacts, while also providing meaningful and timely risk reduction, the necessary dam safety improvements will be sequenced as follows:
- First Set of Works (started in March 2023)
- Second Set of Works (targeted to start as early as 2026)
Construction of the First Set of Works requires a temporary closure of the tunnel but does not require a deep or extensive drawdown of the Alouette Lake Reservoir. This work will mainly occur at the Stave Lake Reservoir end of the tunnel. It will include seismic upgrades to the surge tower, surge shaft, and improved reliability of the adit gate.
Construction for the Second Set of Works will include seismic upgrades to the headworks tower and headworks shaft, the power tunnel and construction adit. This work will require reservoir management, including drawdowns of the Alouette Lake Reservoir. This work will occur mainly at the Alouette Lake Reservoir side of the tunnel.
Reservoir management: three options
We've identified three options for reservoir management that would allow the construction of the Second Set of Works to be completed safely. Options 2 and 3 require extended drawdowns of the Alouette Lake Reservoir below our normal Water Use Plan Order summer recreation level constraints. Options 1 and 3 increase water going down the South Alouette River.
This option would not require the reservoir to be lowered during the summer months. It does keep the tunnel closed between July 1 and December 31 whereas it would be open part of this time during normal operations. The water that would typically pass through the tunnel when Alouette Lake Reservoir is above 122.6 metres would be passed to the South Alouette River, resulting in flows of up to ~43 m3/second compared to the ~2.7 m3/second for fish flows during normal operations between June 15 and December 31.
This option requires a change to operations at Alouette Lake Reservoir and closing the tunnel between it and Stave Lake reservoir from July 15 to October 31. The reservoir would be lowered to 116.5 metres between June 15 and July 15. During normal operations, the minimum reservoir elevation during this time ranges from 121.25 metres to 122.5 metres to support recreational use of the reservoir. With this option, ~2.2 m3/second would be passed to the South Alouette River for fish flows.
This option is similar to option 2 and would involve lowering Alouette Lake Reservoir to 118 metres (compared to 116.5 metres in option 2) between June 15 and July 1. The tunnel between Alouette Lake and Stave Lake reservoirs would be closed from July 1 to October 31. With this option, up to ~7 metre3/s of water would be going down the South Alouette River.
Consultation and evaluation
We held a public information session in 2021 to present the three potential reservoir management options.
The potential environmental and archaeological impacts associated with each reservoir management option have been reviewed and summarized in a preliminary assessment of impacts report which has been provided to Indigenous Nation, regulators and stakeholders for feedback. All three options have potential impacts. The assessment and feedback will be used to inform a structured decision-making process for the selection of a preferred option.
After the preferred option is selected, further assessment will be completed to fully understand potential impacts and facilitate additional consultation and engagement.