“The award recognizes excellence, northern innovations/adaptation, sustainability, service to the community and enhancement to the quality of life through engineering in Yukon.”
Benefits of the Mayo River Flood Control Project
The Mayo River Flood Control Project has significantly contributed to protecting the Village of Mayo against adverse effects related to winter flooding on the River. It has provided future recreational opportunities near the lower Mayo River, allowing access to this natural area for residents. New trails now give residents the ability to enjoy this natural setting along the river.
Sustainability and environmental protection are key elements of the project. For example, construction was completed over a tight 6-week schedule to accommodate the fish timing window for instream works.
The project has also allowed Yukon Energy to increase their renewable energy generation from the Mayo hydroelectric facility during winter months, reducing reliance on thermal electrical generation (LNG or diesel).
Award-Winning Engineering
Morrison Hershfield received the 2017 Yukon Engineering Excellence Award recognizing the Mayo River Flood Control Project for Excellence in Engineering as it applies to Yukon’s Northern climate and terrain.
The Yukon Engineering Excellence Award is presented to projects that are sustainable, considerate of the environment, serve the community and demonstrate how engineering can enhance quality of life for communities.
The project demonstrates applied research, design, innovation, construction and project management approach that represents a truly “unique Yukon and Northern solution” to a difficult challenge for the government of Yukon.
The Mayo River
The flow of the Mayo River is controlled by the Mayo Generating Station, located approximately 13 km upstream from the Village of Mayo, which is owned and operated by the Yukon Energy Corporation (YEC). The small wandering gravel bed river is very shallow which makes winter hydro operations challenging. In fact, hydropower production on such small northern rivers is uncommon.
Winter Ice-Related Flooding Challenges
The lower reach of the Mayo River in the vicinity of the village has been subject to significant winter flooding related to the development of ice jams, particularly between 2010 and 2014. This has resulted in significant challenges for the community and stakeholders, including:
- Flooding of private and public properties (residences, infrastructure, a diesel plant, roads and trails)
- Significant capital costs to the Yukon Government for emergency flood relief efforts (including extensive ice removal)
- Reduction in winter generation at Yukon Energy’s Mayo Generating Station over at least 4 winters
- Ongoing community concerns over winter months and stress within the community
Measures for Flood Protection
The Government of Yukon Department of Community Services, Infrastructure Development Branch (YG-CS) has a mandate in place to support communities through the provision of flood protection infrastructure where needed.
In 2014, Morrison Hershfield was hired by YG-CS to complete the preliminary design of long term flood mitigation solutions for the Mayo River. The goal of the project was to reduce or eliminate flooding in the Village of Mayo, while minimizing human intervention and providing the opportunity to maximize hydroelectric generation during the winter.
Given the complexity of the issue and high degree of uncertainty, Morrison Hershfield identified a series of measures that could be implemented incrementally. These measures included:
- Develop and implement a winter operation protocol
- Increase hydraulic capacity of Mayo River
- Provide bank stabilization
- Permanently establish diversion channels
Flow Management
During the study, it was discovered that the Mayo River ice cover forms primarily through shore ice growth. This pattern is unique when compared to many rivers that form an ice cover by frazil ice accumulation. This finding helped focus the flow management protocol to promote the formation of a stable ice cover.
The flow management procedure has shown good results over the last three winter seasons, during which time only minor localized flooding has occurred and there has not been any significant risk to infrastructure within the Village of Mayo.
Yukon Energy Corporation was also able to increase hydro electrical generation relative to the previous winters (2010 through 2014) by mitigating the significant flooding that had previously limited power generation potential.
Keeping it Local
Morrison Hershfield completed detail design of the long-term flood mitigation works in 2016, with much of the construction being completed during the summer months.
It is significant to note that the construction of the permanent works was completed entirely by contractors from the Mayo area, Ewing Transport and Wilf’s Contracting. A forward thinking project management approach by Yukon Government, leveraging local resources from the Village. As a result, the expertise gained from this project has stayed within the community and it will ease future maintenance and monitoring of the river.
Flood Mitigation Works
The works consisted of:
- Construction of access roads for permanent year-round access.
- Placement of culverts to provide permanent crossings over two side channels used as fish rearing habitats.
- Sediment removal in six zones along the lower Mayo River that were previously identified as the most problematic areas for ice jamming.
- Bank protection with riprap to protect banks that were stripped of vegetation during previous emergency flood mitigation efforts.
- Stabilization of the emergency diversion channels constructed in 2011 to establish them as permanent overflow channels providing additional hydraulic capacity in case of high water levels associated with flooding.
The Team, based out of our Whitehorse office, is honored to be recognized for their work and are looking forward to continuing to better the community through their difference making engineering solutions.
