As southern Pakistan grapples with deadly floods along the Indus River, residents of another country with a long history of flooding may wonder if it could happen here.
With three coasts, nearly 900,000 lakes and more than 8,500 rivers, major flooding is part of Canada’s past and future.
According to Public Safety Canada, these are also the costliest and most common natural disasters in Canada, affecting hundreds of thousands of Canadians.
“There are urban areas across the country that are all dealing with flooding,” Jennifer Drake, a professor at Carleton University, told CTVNews.ca in a phone interview Friday. “But the causes of flooding can vary by climate and region.”
Here are the types of areas in Canada most likely to experience flooding.
While many people associate the word “delta” with the Mississippi River, John Richardson, who teaches in the Department of Forest Conservation Sciences at the University of British Columbia, says that Canada has many deltas and that they are generally prone to flooding.
According to Richardson, river deltas form where the flow of a river slows as it reaches the body of water it is discharging into, causing that flow to spread out over a larger area and deposit sediments that eventually become a landmass.
“A lot of places in Canada where we see big floods are largely in these delta-like areas,” Richardson told CTVNews.ca in a phone interview Friday. “What’s important is to think that river deltas don’t just flow into the ocean. River deltas also in other rivers, in lakes and wetlands.
Deltas are particularly prone to flooding when water levels rise, either in the river or in the body of water into which it flows. This flooding, he said, has caused problems for communities located in Canadian deltas, such as those along the Fraser Delta in British Columbia.
Flat, shallow areas adjacent to rivers, called floodplains, are particularly prone to flooding during storms, spring ice melt, or any other event that causes water levels to rise above the bank.
“The name says it all,” Richardson said. “Floodplains have been established over thousands of years from streams carrying sediments from which they are eroded.”
Richardson said they have always been attractive places to settle because the floodplain soil is good for farming.
“So we had a history as construction humans in those areas.”
Richardson said communities in floodplains are at risk from water level changes caused by storms and spring ice melt, not just because of the risk of a river overflowing its banks, but because that these water level changes prevent storm sewers from flowing properly, resulting in urban flooding.
Several communities in Toronto were devastated by historic flooding during Hurricane Hazel in October 1954. This event killed more than 80 people, left thousands homeless and destroyed bridges and roads in western town, near the floodplain of the River Humber.
RIVERS FLOWING IN THE NORTH
According to Drake, spring brings additional risks to communities along the rivers in the form of spring floods or thaws and the accompanying ice jams. While floods can cause water levels to rise, ice jams create natural dams that impede the flow of water in the river.
“Jail jams are when you have this surface ice on a river that breaks up and gets stuck like an ice jam, and causes the water to flow back behind it,” said Drake, who teaches in the department of civil and environmental engineering at Carleton University. “They are difficult to predict.”
Water trapped by ice jams can flow down the banks of a river, impacting nearby communities.
Although ice jams can occur on any river that freezes over during the winter, north-flowing rivers, such as the Mackenzie River, are particularly prone to it. Indeed, the water upstream in the south thaws more quickly than the water downstream in the north, which contributes to the formation of ice jams and increases the risk of local flooding.
Notable examples of major floods in north-flowing rivers include the 1950 Red River flood in Winnipeg and the Red River Valley; the 2020 Athabasca River flood in Fort McMurray, Alberta; and annual flooding along the Mackenzie, Hay and Peace rivers in Alberta and the Northwest Territories.
Along Canada’s coasts, storms bring the risk of atmospheric surges that can push seawater toward the ground.
“The rising water level that occurs during a hurricane or large storm creates flooding or exacerbates flooding in coastal cities,” Drake said.
In January 2000, a record storm surge in New Brunswick caused over $1.7 million in damage to communities from Shediac to Bathurst.
Richardson expects to see storm records broken with increasing regularity across the country as climate change intensifies.
“We all know that with climate change, we’re predicting stronger storms,” Richardson said. “Even if you look at hurricane intensities, they have been increasing in average intensity for most of the last 40 years.”