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 repaired the structure in 2021 and 2022 but, in December 2023, an engineering assessment found that the spillway had deteriorated beyond the point of repair, and that the spillway needed to be replaced. We immediately started planning and designing for the new spillway, and have started construction work that does not require additional licences, permits, or work in the water.

Should I be worried about flooding or my personal safety?

No. While risks to public 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.

What is Yukon Energy doing to prepare for a potential emergency?

Yukon Energy completes regular inspections of the spillway, ranging from daily site checks to annual engineering reviews by its own dam safety engineer and external experts. We also monitor key instruments monthly to detect any early warning signs. In addition, Yukon Energy's contractor that is currently working on the rock slope at the dam keeps equipment on site that can be used quickly if a rapid response is ever needed.

Yukon Energy has also updated its Emergency Preparedness Plan for the Mayo hydro facility. In May of this year, we participated in a tabletop exercise led by the Government of Yukon's Emergency Measures Organization where we walked through the steps all parties would take in the event that the spillway or dam failed and fast flowing water started to move towards Mayo. Planning for these types of situations is normal for hydro utilities like Yukon Energy.

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

Yukon Energy recognizes the First Nation of Na-Cho Nyäk Dun (FNNND)'s strong interest in upstream fish passage at the Wareham dam. While Yukon Energy has no regulatory obligation to install upstream fish passage, we are working with technical specialists and engaging with the FNNND on potential options. 

What's the plan going forward?

Yukon Energy is evaluating two potential options to replace the spillway. We will continue to work with the First Nation of Na-Cho Nyäk Dun and the Village of Mayo throughout the process.