With three coasts, nearly 900,000 lakes and more than 8,500 rivers, significant flooding is part of Canada’s past and future.
They are also Canada’s costliest and most common natural hazards, according to Public Safety Canada, affecting hundreds of thousands of Canadians.
“There are urban areas across the country that experience all the flooding,” Carleton University professor Jennifer Drake 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 that are most likely to experience flooding.
RIVER DELTA
While many people associate the word “delta” with the Mississippi River, John Richardson, who teaches in the University of British Columbia’s forest conservation sciences department, says Canada has many deltas and they are usually prone to flooding.
According to Richardson, river deltas form where the flow of a river slows as it reaches the body of water it drains into, causing that flow to spread over a larger area and deposit sediments that eventually become dry land.
“A lot of the places in Canada where we see major flooding are very much in these delta-type areas,” Richardson told CTVNews.ca in a phone interview Friday. “What is important is to think about river deltas not just going to 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 the body of water it flows into. That flooding, he said, has caused problems in communities located in Canada’s deltas, such as those along the Fraser Delta in British Columbia.
Flooded farmland is seen along the Fraser River in an aerial view near Abbotsford, BC, Wednesday, May 16, 2018. THE CANADIAN PRESS/Darryl Dyck
FLOODS
Flat, shallow areas of land next to rivers, known as floodplains, are particularly prone to flooding during storms, spring ice melt, or any other event that causes water levels to exceed river banks.
“The name says it all,” Richardson said. “Floodplains were established over thousands of years by streams carrying sediment downstream where it erodes.”
Richardson said they were historically attractive places to settle because the soil in the floodplains is good for farming.
“So we have a history as humans of building in these areas.”
Richardson said floodplain communities are threatened by changes in water levels caused by storms and spring ice melt, not only because of the risk of a river overflowing its banks, but because those changes in water levels prevent proper drainage of storm drains, leading to 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 the west end of the city near the Humber River floodplain.
RIVERS WITH A NORTH FLOW
According to Drake, spring brings additional risks to communities along rivers in the form of fresh or spring thaws and accompanying ice jams. While ice jams can raise water levels, ice jams create natural dams that prevent water from flowing through the river.
“Ice jams are when you have this surface ice in a river that breaks up and sticks like log jam, and forces the water behind it to come back up,” said Drake, who teaches in Carleton University’s civil and environmental engineering department. “These are hard to predict.”
Water blocked by ice jams can flow over the banks of a river, affecting nearby communities.
While 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 them. This is because water upstream to the south thaws faster than water downstream to the north, contributing to the accumulation of ice jams and increasing the risk of localized 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, Alta. and annual flooding along the Mackenzie, Hay and Peace rivers in Alberta and the Northwest Territories.
Along Canada’s coast, storms bring the risk of atmospheric surges that can push seawater ashore.
“The rise in water levels that happens when you have a hurricane or a major storm creates flooding or exacerbates flooding for coastal cities,” Drake said.
In January 2000, a record storm event in New Brunswick caused more than $1.7 million in damage to communities from Shediac to Bathurst.
Richardson expects to see storm records being broken with increasing regularity across the country as climate change intensifies.
“We all know that with climate change we expect stronger storms,” Richardson said. “Even if you look at hurricane intensities, they’ve been increasing in average intensity for most of the last 40 years.”
