Muskrat Falls Hydroelectric Project

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The Muskrat Falls Hydroelectric Project is part of Newfoundland and Labrador’s plan to be a clean energy leader. Power from the project can displace an estimated three to four megatons of carbon dioxide annually from thermal generating facilities. Put another way, the estimated carbon footprint reduction throughout northeastern Canada and the United States is equivalent to taking almost one million cars off the road each year.

Our role was to complete the final engineering design of the Muskrat Falls project and then support the project through construction and commissioning. Our engineering services during the design phase included final optimization of the type and layout of the hydro project components. Design and construction drawings were developed to a "ready-for-construction" stage, which resulted in very little design change during construction.

We also provided engineering support during construction to ensure the design intent was met and the integrity of the design was maintained. The support tasks included reviewing all contractor document submittals, design changes during construction to address changed conditions, and support during commissioning.

Sited in the Churchill River, the Muskrat Falls project is an 824-megawatt hydroelectric generating facility. The project has a live storage of 50 million m3 of water and a total spillway discharge capacity of 25,000 m3/s. It consists of several key components:

An 84 m tall, 78 m wide Powerhouse structure containing four 206 MW close-coupled Kaplan turbine-generators with 660 m3/s capacity producing a total of 824 MW, with an annual output of 4.9 TeraWatt hours.
The North Dam, a 35 m high, 450 m long roller-compacted concrete (RCC) dam with a 330 m overflow crest at an elevation of 39.3 m. This RCC structure took 250,000 m3 of concrete to complete, and the dam can be used as a stepped spillway during significant floods. The energy dissipation is ensured by a flip bucket at the end of the stepped chute which projects the flow jet to a safe distance from the dam.
The South Dam, a 20 m high, 240 m long, 135,000 m³ zoned earthfill dam. This dam closes the south part of the reservoir between the bank and the powerhouse and holds the water in the reservoir. It is a conventional rock-fill dam constructed by building up layers of rock and till material on the underlying bedrock, which serves as a foundation for the dam. A road built on top provides access to the powerhouse intake and the gated spillway.
The North Spur is a natural earth dam that constricts the river at the project location and is a critical feature of this hydropower facility. Approximately 1,000 m long, 500 m wide and 45 m to 60 m high, it consists of unconsolidated mixed sand, marine silt, and clay. We had to stabilize this natural feature so that it would act as a dam, a particularly challenging but crucial aspect of the project, because the upstream water level had to be raised by more than 22 m
The Gated Spillway 40 m high and 75 m wide and is the primary release of water from the reservoir. It consists of 5 vertical lift gates, each 23 m high by 10.5 m wide, with unit spill capacity among the highest in the world at 273 m3/s per meter width.

Beyond the infrastructure at Muskrat Falls itself, the overall project also includes over 1,600 km of transmission lines across the province (including a subsea transmission link connecting Labrador to the island), HVDC (high voltage direct current) installations including converter stations, and the Maritime Link transmission line, developed by Emera Inc, connecting Newfoundland and Nova Scotia.

Challenges and Innovation: From Flip Buckets to Frazil Ice

We view challenges as opportunities to take apart the usual way of doing things and finding better solutions. For this project, that meant rethinking how to safely dissipate the energy of a mighty river in flood.

The North Dam can be used as a stepped spillway during major floods to supplement the gated spillway. The steps dissipate energy for lower floods. However, at design conditions, skip flow is observed with only an insignificant amount of energy dissipated at the steps. The solution was to add a flip bucket at the end of the spillway chute. This device helps project the flow jet to a safe distance from the toe of the dam keeping the dam foundations safe from erosion. We tested our innovation on numerical and physical models to make sure it would satisfy the design criteria.

Imagine having to pour 250,000 m3 of concrete in the short construction season of subarctic Labrador. Now add the requirement of a very specific design that included the steps and flip bucket. Clearly, finding ways to do this quickly but accurately would be a challenge. As part of the project team, we worked closely with the contractor to find practical solutions. This included an optimization of the step height to strike a balance between the hydraulic performance and construction simplicity. As a result, the speed of construction was among the fastest in the world for a RCC dam of this size.

In winter, frazil ice—loose, slushy ice that forms on the river and sticks to everything—forms upstream in the lower Churchill River. This ice flowing into the deep pool immediately downstream of Muskrat Falls created conditions perfect for ice buildup and jamming. The flow restriction causes the water level upstream of the ice dam to rise significantly, in some years by more than 15 meters, drowning out the Lower Falls and sometimes the Upper Falls. An innovative ice management program was developed to manage and eliminate the jam and complete the construction. This included building a RCC cofferdam dam to protect the working area during the spillway construction. Once constructed, the river was diverted through it by closing the river with a series of cofferdams. The spillway gates were then operated to partially impound the headrace and to maintain the upstream water level during wintertime to control and reduce the frazil ice. The approach proved to be very effective in managing the water levels at the construction site throughout the year.

Dam Safety and Safety during Construction

Four groups of independent experts reviewed the design during its development, and we used state-of-the-art techniques to develop and validate our design approach.

From stabilizing the North Spur, studying landslide-generated waves upstream of the site to installing specialized instruments at critical locations to monitor behavior during the first phase of impoundment and on a long-term basis, we made sure of the integrity and stability of the site water retaining structures. The dam safety team used the data together with visual inspections to continuously monitor the North Spur to confirm this challenging semi-natural structure acting as a dam was behaving as expected. The dam safety program also monitored the other temporary and permanent closure structures to ensure they remained stable and safe.

The dam safety program provided surveillance and monitoring of all the facilities, both temporary and permanent. The program included installing extensive instrumentation for monitoring the structures, review of the observations, and regular reporting to project management. External audits and reviews of the dam safety program at Muskrat Falls during construction found the program to be robust and effective in monitoring all structures for the project.

The safety-first culture throughout the construction of this project led to an exemplary safety record: 14 M hours without a lost-time incident. The overall Lost Time Injury Frequency (LTIF) was 0.06, far below the Canadian Construction LTIF of 1.12.

Why does it matter?

Waterpower is a critical renewable resource that helps meet our present and future electricity needs.

Adding the generation from Muskrat Falls Hydroelectric Project means 98% of Labrador and Newfoundland’s energy is generated from renewable energy sources. It will also allow generation at the aging Holyrood Thermal Generating station to be shut down. Thanks to Muskrat Falls and the other hydroelectric facilities across the province, Newfoundland and Labrador’s energy grid continues to be one of the cleanest in the world.

This also extends to the project’s direct impact on the river. The Environmental Management System (EMS) that was implemented ensured the project achieved its environmental goals through consistent control of construction activities and enabled the project to reduce its environmental impacts. As the project is run-of-river, it has relatively limited impact from the impoundment, and environmental surveys in the river confirmed that there was minimal impact. Moreover, the project also included the design and implementation of fish habitat enhancement at the tributaries in the upstream end of the reservoir further offsetting the impact of the impoundment. Follow-up have been done to evaluate changes, particularly in the water quality, and confirm that these were minimal.

Our work on this project lead to us publishing and presenting 24 technical papers on various aspects of the design and construction, adding useful research and insight to the dam engineering community. The project also employed many students from the Memorial University of Newfoundland, providing valuable experience for these students and enhancing their awareness of the dam engineering profession.

"With the completion of the Muskrat Falls Project, Newfoundland and Labrador will be a leader in clean energy. This will reduce greenhouse gas emissions and the carbon footprint throughout Northeastern Canada and the United States – equivalent to taking almost one million cars off the road for one year." –Excerpt Environment | Nalcor Energy – Lower Churchill Project

Awards:

The North and South Dams won the 2019 Engineering News-Record Global Best Project: Dam.

The Muskrat Falls Hydroelectric Project won the 2022 Best Constructed Project Award from the Canadian Dam Association.

824 MW

Generating Facility

1,600 km

Transmission Line

Markets

Power & renewables
Location

Happy Valley-Goose Bay, Newfoundland and Labrador, Canada
Client

Newfoundland & Labrador Hydro
Completion date

2023

Greg Snyder

Senior Technical Expert, Hydro, Canada contact form

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Muskrat Falls Hydroelectric Project

Challenges and Innovation: From Flip Buckets to Frazil Ice

Why does it matter?

Greg Snyder

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