Ever since the devastating spring floods of 2020 in Fort McMurray, the northeastern Alberta community has been shoring up its defences against rising rivers.
Now, officials with the Regional Municipality of Wood Buffalo (RMWB) say Fort McMurray is better prepared for future floods.
“From a permanent structural mitigation standpoint, there’s been significant works completed,” said James Semple, manager of RMWB’s project management office.
It has spent $119 million on flood mitigation so far; the remaining work that is planned will bring the total expenditure to about $270 million, according to a statement on the RMWB’s website.
Semple said the aim is to prepare the community for another one-in-100-year flood — which is what Fort McMurray experienced in 2020 — as well as a one-in-200-year flood, in which the river would rise by another half-metre or so.
Preparation means damages to residents and businesses would be appropriately mitigated, he said.
Vulnerable location
Fort McMurray sits at the confluence of the Athabasca and Clearwater rivers. When ice on these two rivers breaks up in the spring, it can create literal dams in the river. As water backs up, it eventually overflows the banks and can flood low-lying parts of town.
Ice jams tend to form downstream of Fort McMurray, where the Athabasca changes shape, said Nadia Kovachis, a river hydraulics and ice engineer with Alberta River Forecast Centre.
“The river really flattens out, which encourages sediment deposition, and this causes the river to be wider, with many more sandbars and islands. And these things kind of all work together to encourage ice jam formation,” she said.
Fort McMurray has a long history of spring floods caused by ice jams on the Athabasca River, with records of extreme incidents going back to 1835. Of 17 notable floods since then, 16 were caused by ice jams.
The 2020 flood was caused by a massive 25-kilometre ice jam on the Athabasca. Water from both rivers spilled into downtown, forced about 12,000 people from their homes and caused more than $520 million in insured damage.
After the 2020 flood, an engineering report found that the municipality’s flood mitigation system was incomplete and flawed.
Kovachis said it’s difficult to predict when ice jam flooding will happen. That’s why the mitigation measures are so important.
More infrastructure being built
In September, the RMWB council approved going ahead with structural mitigation between the Clearwater River and nearby Clearwater Drive. This work is the final phase of permanent flood mitigation efforts for downtown Fort McMurray, the municipality said.
Options for this stretch of work include earth berms and retaining walls, the municipality said. Construction is expected to begin next year. The Heritage Shipyard, which houses a collection of historical vessels that used to navigate the Athabasca River, will be relocated to make space for the infrastructure.
Fort McMurray’s flood mitigation system is a combination of berms, walls, “the raising of roads, and a variation of different things,” said Semple.
The goal is “to bring [up] the level around the lower townsite and other areas that are susceptible to flood, bring them up to a level where it reduces the risk of flooding.”
A man-made berm is made of clay and soil and looks like a hill or barrier, with vegetation growing on it. Semple said a berm could withstand an eight to 10 metres rise in water levels, preventing water from inundating that part of the municipality.
The normal water level in Fort McMurray rivers is about 240 metres above sea level. The 2020 flood saw water level rise to about 250 metres.
Fort McMurray stands at the confluence of two rivers — Athabasca and Clearwater. During the spring thaw, ice can jam the rivers and flood parts of the city. CBC’s Dennis Kovtun explains what Fort McMurray is doing to avoid this.
Another flood mitigation measure is an anti-flood wall, which is prominently visible at the intersection of Gordon Avenue and Riedel Streets. It serves as a walkway for residents.
There are also temporary barriers that look like mini-berms, which are prominent in the Heritage Shipyard area.
Erin Sieger, the RMWB’s director of emergency management, said the municipality starts preparing in earnest for a possible flood season in early spring.
“In terms of river break-up season, we start getting ready for that in early March, where we reignite our relationships with the river forecasters and start to talk with stakeholders and partners in the region about what they’re doing to prepare and how we can help,” she said.
Kovachis said there are “no long-lead indicators” that would help predict the flooding well in advance.
How much snow is left on the ground — and how quickly it melts — play a key role, she said.
“In 2020, we had a really cold late March and early April,” she said.
Then the temperatures rose quickly. The thickness of the snowpack was higher than average, and the ice on the river was thick as well.
“So, all of those things worked together for the severity.”