Melting ice and flood risk: How ice jams can endanger Canadian communities
When an ice jam forms it acts like a temporary dam, creating an obstruction that can cause water levels to rise, possibly spilling onto adjacent communities.
The forecast is setting the stage for ice jams to occur in flood-prone areas of southern Ontario this week.
Sunday's deep freeze, followed by warming temperatures and possible rainfall, could melt snow and weaken river ice in the days ahead, mobilising chunks of ice that can pile up at ends and bridges in the river, leading to potential floods.
The Grand River Conservation Authority (GRCA) has issued a flood watch ahead of this week's rain in southern Ontario.
"The river system is largely ice covered and there is a heavy snowpack across most of the watershed," reads part of the flood watch statement.
"The warm conditions and rain will generate runoff and will likely be sufficient to cause the river ice cover to break up and start moving, which raises the risk of ice jam formation and associated flood potential."
What is an ice jam?
Ice jams, also sometimes called ice dams, occur when large pieces of ice come together and obstruct the flow of water in a river, which can cause flooding in nearby communities.
It's common in Canada in late winter and early spring as the temperature warms and snow and ice melt.
When an ice jam forms it acts like a temporary dam, creating an obstruction that can cause water levels to rise, possibly spilling onto adjacent communities.
Reducing ice jam risk
City planners often employ several strategies to mitigate the risk posed by ice jams, including monitoring the weather conditions and breaking up ice. In some areas, flood control infrastructure, including flood channels and berms, are installed.
"Residents who typically experience flooding should be prepared as conditions can change quickly and without warning," GRCA says on its website.
"Residents are encouraged to familiarize themselves with their local municipal flood response programs and be prepared for flooding due to the elevated risk with this event. High flows and unstable ice conditions will increase the safety risk around rivers and streams throughout the watershed."
Fort McMurray is an example of the dangers ice jams pose
In some cases, ice jams can cause widespread damage to infrastructure, displace residents, and lead to hundreds of millions of dollars in damages.
A recent example in Canada occurred in Fort McMurray, Alberta, between April 26 and May 2, 2020.
Several ice jams on the Athabasca River caused "catastrophic" flooding in downtown Fort McMurray, damaging more than 1,200 properties, displacing around 13,000 people, and prompting more than seven weeks of boil water advisories.
A 2021 report estimated the total insured and uninsured losses from the event exceeded CAD 1.1 billion.
A glimpse at the flooding caused by an ice jam in Fort McMurray, Alberta in April 2020. (McMurray Aviation)
One man died while riding his ATV on a trail. Water levels unexpectedly rose, and he was swept into the Athabasca River. Another man involved in the incident survived.
Header image: File photo via Canva Pro.