In the heart of eastern Manitoba’s rugged Canadian Shield, a powerful waterway cuts a channel through rocky, uneven landscape. Once a key transportation route, in more recent history, the Winnipeg River has been critical to the province’s energy needs.

More than 90 years ago, Winnipeg’s reputation as a hydroelectric-powered city was bolstered when the Slave Falls Generating Station, 160 kilometers northeast of Winnipeg, started harnessing the power of the Winnipeg River. Opened in 1931, the same year as the Seven Sisters Generating Station on the Winnipeg River, the fourth and fifth dams ensured there was enough electricity to meet the demand of the then-boomtown.

But nature and time have not been friendly to the impressive but aging structure.

In 2018, an assessment found much of the foundation was in poor condition because of water seeping into small pores, then freezing and expanding, causing cracks.

“The concrete that the girders were sitting on seemed very deteriorated and caused a lot of concern,” says Rick Maloney, project manager for Manitoba Hydro. “It's basically like those piers are rotting from the inside out. They’re big piers and that's probably why we haven't seen any sort of failure to this point, but we had to do some work there.”

It was clear, repairs would be a major undertaking. Manitoba Hydro – the owner and primary contractor – decided a tower crane was needed to move materials around the site over the course of the multi-year project.

When repairs are needed to dams, cranes can typically be erected on the deck of the structure itself or on land nearby. In this case, neither of those would work. For one, the original dam itself wasn’t designed to hold that kind of weight. That concern was exacerbated by the deteriorating state of the foundation. On top of that, the multi-year rehabilitation project had to be done with minimal disruption to regular operations — and the crane had to be able to reach across the entire structure. 

So there was only one place that would work.

“To reach the whole site, we needed to get this tower crane into the water,” says Maloney.

“So the challenge was building a tower crane foundation in water with a depth of between five and 15 feet, downstream of an operating power plant,” recalls Brad Mackid, PCL construction manager for Winnipeg civil projects. “We come up with unique ways of building things every day, and this project is a prime example. We had to figure out what made sense and how to build it.”

An engineering firm hired by Manitoba Hydro designed the concrete pedestal for the 104-foot tower crane, and in early 2023, it was up to PCL to find a way to get the job done.

PCL’s solution was a combination of technology and human ingenuity. Brad Mackid decided the easiest way to pour the concrete base was to drop a large metal can — 20 feet in diameter, 34 feet in height — into the river to act as formwork.

The challenge: the can had to sit straight up — plum and level — on a sloped, uneven, rocky riverbed.

“There's nothing around there,” recalls Katja Arnold, project coordinator for PCL in the Winnipeg district. “It’s rocky and on a slope and the Winnipeg River runs through there. So at peak season, it's a pretty steady flow. Water was high on all sides.”

To accurately map the floor of the waterway, the crew drilled through the late winter/early spring ice in regular intervals in a circle with the same circumference as the can, then measured the distance through each hole to the river bottom. By combining those measurements, they were able to create precise GPS data points that mapped out the profile of the riverbed.

Then, the task was transferring that profile onto the can. This is where Mackid really put his engineering degree and experience to the test.

“For each of the GPS data points we calculated an azimuth angle from the center of the can relative to the face of the dam,” he explains. “Using the associated arc distances, we were able to graph the rock profile around the circumference of the can at the design location. By overlaying the bolt pattern of the can over the profile, we were able to scribe the profile directly to the can simply by measuring up from the bottom at each bolt hole location.”

From there, it was a matter of drawing lines between those points – like a child’s “connect the dots” on a much bigger and more complex scale, all the way around the metal can. The profile was then cut by hand, using an angle grinder.

Once the shape of the bottom of the can matched the profile of the riverbed, a crane lifted and lowered it into place, and a Total Station – an advanced, computerized surveying instrument – was used to ensure the 5,700-kilogram can was placed in the exact spot where the measurements were taken.

Making an already challenging endeavor even tougher: there was a tight timeline in place. The work in the water had to be done after the spring thaw and before May 1, when a fish spawning window opens.

“We met all the timelines,” Mackid remembers, with a smile. “There's a very narrow window of opportunity to build this thing where it's not frozen and it's not in the fish window, and it went flawlessly.”

Once the can was down, PCL started a “tremie” concrete pour – a common method for underwater concrete that uses a pipe to push the wet, heavy concrete down to the bottom, displacing water upwards.

The rigidity of the metal can, pinned to the rock below, made perfect formwork for a level, plumb crane base. In July, The Liebherr Litronic 550 tower crane was erected with a 267-foot jib.

“I feel like we say this all the time, but planning and preparation is what makes things successful,” says Arnold. “I give full credit to Brad. He's got over 30 years’ experience, and it showed.”

“I was very impressed with all the planning that went up front, and we saw the benefits of all that planning on the tail end,” says Maloney. “What they did was thinking outside the box. I always appreciate ideas like that coming from a contractor.”

“The beauty of this thing was that we kept it simple,” says Mackid. “I think it was the smartest, easiest, cheapest and safest way to do it.”

The set-up was a success, but PCL’s work isn’t done yet. The company has also been contracted to do structural repairs to the dam’s concrete foundation – using that same tower crane. Phase two: the 7-Bay Sluiceway Structure Rehabilitation project will get underway in early 2025 and is expected to take at least three years.

The dam itself is a small, but important piece of Manitoba’s vast hydroelectric network, and the structure has important historic value. The bottom line: when the multi-billion-dollar crown corporation needs work done on critical assets – it trusts PCL.