Since the devastating spring floods of 2020 in Fort McMurray, northeastern Alberta communities have been strengthening their defenses against rising rivers.
Now, officials with the Regional Municipality of Wood Buffalo (RMWB) say Fort McMurray is well prepared for future flooding.
“From a permanent structural mitigation standpoint, there's significant work done,” said James Semple, manager of the RMWB's Office of Project Management.
It has spent $119 million so far on flood mitigation; According to a statement on the RMWB's website, the remaining planned work will bring the total cost to about $270 million.
Semple said the goal is to prepare the community for another one-in-100-year flood — which Fort McMurray experienced in 2020 — as well as a 200-year flood, in which the river would rise again. Half a meter or so.
Preparation means damage to residents and businesses will be appropriately minimized, he said.
Unsafe location
Fort McMurray sits at the confluence of the Athabasca and Clearwater rivers. When the ice breaks up on these two rivers in the spring, it can create literal dams on the river. When the water backs up, it eventually overflows the banks and can flood low-lying parts of the city.
Ice jams form downstream of Fort McMurray, where the Athabasca changes shape, said Nadia Kovachis, river hydraulics and ice engineer with the Alberta River Forecast Center.
“The river becomes really flat, which encourages sediment deposition, and it widens the river, lots of sand and islands. And all these things work together to encourage ice jam formation,” she said.
Fort McMurray Spring floods caused by ice jams have a long history On the Athabasca River, records of extreme events go back to 1835. Of the 17 notable floods since then, 16 were caused by ice jams.
The 2020 flood was caused by a 25 km long ice jam in the Athabasca. Water from both rivers surged into the city, forcing nearly 12,000 people from their homes and causing more than $520 million in insured damage.
After the 2020 flood, an engineering report found the municipality's flood mitigation system to be incomplete and flawed.
Kovachis said it is difficult to predict when an ice jam flood will occur. This is why mitigation measures are so important.
More infrastructure is being built
In September, the RMWB Council approved moving forward with structural mitigation between the Clearwater River and nearby Clearwater Drive. The work is the final step in permanent flood mitigation efforts for the city of Fort McMurray, the municipality said.
Options for this expansion include earth berms and retaining walls, the municipality said. Construction is expected to begin next year. The Heritage Shipyard, which houses a collection of historic vessels used to navigate the Athabasca River, will be relocated to make room for the infrastructure.
Fort McMurray's flood mitigation system is a combination of berms, walls, “raising roads and different things,” Semple said.
The goal is to “bring (up) the level around low-lying cities and other flood-prone areas, bringing them to a level that reduces the risk of flooding.”
A man-made berm is made of soil and clay and looks like a hill or barrier, with vegetation growing on it. Semple said the berm can withstand an eight to 10 meter rise in water level, preventing water from inundating that part of the municipality.
Normal water levels in Fort McMurray rivers are 240 meters above sea level. The 2020 flood saw water levels rise by around 250 metres.
Fort McMurray stands at the confluence of two rivers – the Athabasca and the Clearwater. During the spring melt, ice can jam rivers and flood parts of the city. CBC's Dennis Kovtun explains what Fort McMurray is doing to avoid it.
Another flood mitigation measure is the anti-flood wall, which can be seen prominently at the intersection of Gordon Avenue and Riddell Street. 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 Seeger, RMWB's director of emergency management, said the municipality will begin preparing for possible flood season in early spring.
“In terms of the river breakup season, we start preparing for that in early March, where we re-establish our relationship with river forecasters and start talking to stakeholders and partners in the region about what they are preparing for and how. We can help, ” she said.
Kovachis said there are “no long lead indicators” that help better predict flooding.
How much snow is left on the ground — and how quickly it melts — plays a key role, she said.
“In 2020, we got really cold in late March and early April,” she said.
Then the temperature rose quickly. Snowpack thickness was above average, and river ice was thick.
“So, all those things worked together for seriousness.”
