Repairs to the Wareham spillway

What is the Wareham spillway?

The Wareham dam and spillway make up part of the Mayo Generating Station and were commissioned in 1952. Just upstream of Wareham dam, water enters an underground pipe that goes to the Mayo A and Mayo B generators to make electricity. When there is too much water to use, it flows down the spillway and back into the Mayo River.

What's happening?

We conduct regular dam safety inspections. After one of these inspections, we noticed there was damage to the concrete on the base of the spillway after high water levels in 2020. We made temporary repairs to the structure in 2021 and 2022 but, in December 2023, an engineering assessment found that the spillway had deteriorated beyond the point of repair. We immediately started planning and design work for the new spillway, and have applied for an emergency amendment to our water licence so that we can start construction.

Should I be worried about flooding or my personal safety?

No. While risks to public and staff safety are increased with the spillway in its current condition, and will increase if this work is 
delayed, Yukon Energy has a fulsome dam monitoring and surveillance program in place, which would alert Yukon Energy staff of any issues before they occurred. In the event of an incident, Yukon Energy would work with the Yukon government’s  Emergency Measures Organization to alert the First Nation of Na-Cho Nyäk Dun, Village of Mayo and the community.

Will Yukon Energy be considering fish passage in the spillway reconstruction?

Yes. Yukon Energy has been working with technical specialists and engaging with the First Nation of Na-Cho Nyäk Dun on design options for the reconstruction of the spillway. We are considering all technically and economically feasible measures to improve downstream fish passage, and will be proceeding with a new horseshoe-shaped, concrete-lined tunnel within the left abutment of the Wareham dam. The tunnel spillway will enhance downstream fish passage, and our work will confirm if additional measures can be implemented to further support the safe, downstream movement of fish.

What's the plan going forward?

Construction is set to begin before the end of 2025 and is expected to be completed by the end of 2029.

We have also developed a monitoring plan to detect any additional damage to the spillway. We will continue to work with the First Nation of Na-Cho Nyäk Dun and the Village of Mayo throughout the process.