All About Flooding

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Depending on where you live, you may have experienced floods over your life or if you’re like me, you only know about flooding and the devastation it causes from the news channel. Flooding can happen in the most unlikely of places so it is important to understand the basics of flooding, no matter where you reside in Canada. According to Public Safety Canada, floods are the most common natural hazard in our country and are an increasing threat to Canadians as extreme weather events become more common. Flooding costs Canadians more than a billion dollars in economic losses every year, and is the most expensive natural disaster to manage and clean-up. 


At the most basic level, flooding is an overflow of water that pushes onto usually dry land. Fluctuations in waterbody levels are natural, but when high water levels threaten homes, lives, or infrastructure, they are considered flood conditions. Floods mostly occur because of water height changes in rivers or lakes as a result of spring snowmelt or heavy precipitation. It is predicted that as the impacts of climate change increase, flood intensity and frequency will also increase across the world in the 21st century.


In the Canadian Prairies, the most common cause of flooding is the build-up of snow and ice over the winter. This winter precipitation collects late fall and winter, and melts into the waterways in a few short weeks in the springtime when temperatures rise. Events that can exacerbate flooding conditions in the spring include heavy rains or ice jams, which can rapidly increase the amount of water flowing into a waterbody. An ice jam is when there is an obstruction to the flow of water due to blocks of ice. Floods may also be the result of a dam breakage or failure, or excessive melting of glaciers as mean temperatures rise all around the earth.


Spring melting in Edmonton in 2018. Image credit: Kurt Bauschardt from Flickr, unedited.


River flooding can occur as a result of this spring melting and increased precipitation, but other factors can influence how much water runoff enters the river. There can be more water runoff flowing into the river as a result of increased urbanization, which can alter the landscape’s vegetation. In the process of urbanization surfaces change from soft surfaces that absorb water to hard surfaces which absorb less or no water, such as cement. Soft surfaces like grass or soil are beneficial because they decrease the runoff moving into waterways. Some cities have bylaws that outline what percentage of a house yard has to be soft surface, to reduce water runoff. Vegetation also makes a difference in runoff rates, as water moves faster over sparse land (such as cropland) than forested land. Forests have less water runoff because they have barriers such as trees and shrubs that absorb the water and slow the runoff speed.


The Red River in Winnipeg meeting the Assiniboine River, during a flooding event in the spring of 2017. Image credit: Murray Foubister from Flickr, unedited. 


On lakes there can also be a rise in the water level, which can cause damage to the shorelines, cottages, and businesses. Increases in lake water can be a result of increased water in the river that feeds into the lake or an especially snowy winter. Lakes can flood over just like a river, though lake water levels rise much slower so individuals are able to anticipate the flooding and put in place measures to prevent damage. An example of an unusually high lake this year is Lake Ontario and some of the other Great Lakes.


Lake Ontario in May 2017, when the high water covered what was a public beach area. The conditions of this image are similar to this year. Image credit: Lincoln Spaulding from Flickr, unedited.


Flash floods can occur quickly when heavy storms or spring melt significantly increase the amount of runoff. In Canada, flash floods are a risk for many citizens as they can occur nearly anywhere. In Canadian landscapes the depth of the snow, snow water content, time the snow takes to melt, and local topography can be determining factors for a flash flood in the spring. Flash flooding in urban areas is especially a concern, as many Canadian cities and towns were built around rivers, lakes, and harbours due to the ease of commerce and transportation in the past, among other reasons. 


A flash flood in Quebec in 2017. Image credit: Gone Coastal from Flickr, unedited. 


Traditionally, policy makers have responded to flooding by attempting to control the water flow with dams or dikes to move the water away from the area with high flood risk. A dam is a barrier constructed to hold back water on a river to suppress floods, and may also be used to generate electricity or hold water for water supply or irrigation. A dike is a long wall or embankment that is built to prevent possible flooding from a river, lake, ocean, or sea. There is limited evidence to suggest that these are the best ways to manage floods, as floods are unpredictable and extremely low-probability floods occur. An example of a low probability flood occurring recently is the Calgary flood of 2013. Heavy rainfall on the melting snow of the Rocky Mountains combined with steep and rocky terrain facilitated the perfect mix of conditions for flooding in several southern Alberta watersheds. This was the largest flood Calgary had seen since 1932, and cost $6 billion in financial losses and property damage. Since this flood, Calgary has invested in flood mitigation and resilience projects to be ready when the next flood strikes.


The Bow River is nearly touching the Calgary Peace Bridge in the 2013 Floods. Image credit: Ryan Reynolds from Flickr, unedited.


In 1975, the federal government announced a flood damage reduction program for Canada. The main project within this plan was the creation of publicly accessible flood-risk maps to identify hazardous areas. These maps are used by flood-plain managers, urban planners, property developers and the public when deciding projects or buying a home. In 2020 we can look forward to the government releasing new floodplain maps which will be easily accessible to the public online, and updated with the latest geospatial data. These maps are a valuable tool that can steer the decision-making of developers, businesses, and landowners when looking at properties in and around flood-prone areas. Choosing how, where, and when to develop around water can affect your community. By keeping flood hazard areas in mind, infrastructure flooding can be prevented and reinforce the natural environment around your waterbody.


Canadian flood events of the past were what inspired the government to create a program to encourage informed building in high-risk flood areas. Many of these historic flood events happened on large river systems which passed through urban areas, with one particular flood taking place with North Saskatchewan River running through Edmonton. In June of 1915, the North Saskatchewan River rose steadily in Edmonton peaking at 10 meters above its usual height! The water swept away lumber mills, brick yards, a brewery, and many houses that lie in the river valley. The image below shows how the Canadian Northern Railway parked train cars on the Low Level Bridge to protect the bridge against the debris hitting its piers. No lives were lost in this flooding, but it did cost an estimated $647 M dollars in damage (adjusted for inflation) and left around 2000 people without homes. This event shaped Edmonton’s future as people moved inland to redevelop their businesses and homes, and therefore slowed development in the river valley. This flood is one of the reasons why Edmonton has such an extensive park system, rather than human development today.


Image Credit: City of Edmonton Archives (Image EA- 160-1399).


Another more recent flood event experienced in the prairies includes the 1997 Red River Flood, which affected Minnesota, North Dakota, and Southern Manitoba. This flood was the result of abundant snowfall in the winter and unusually high temperatures speeding up the spring melt. South of Winnipeg, Manitoba has an extensive dike and diversion system called the Red River Floodway. This system collects the floodwater moving in from the Red River and diverts it around the city of Winnipeg, where it is released back into the Red River, preventing flooding of the city.  Even with these flood protection measures in place, the river flooded from the south through the dike system, all the way up to Winnipeg. This flood event was deemed a 100-year flood, which means it is a flood event that has a 1% chance of being equalled or exceeded in any given year!


The Red River Floodway depicted on a map. Image Credit: Karl Musser via Wikipedia, Red River Floodway.


The Red River Floodway, also known as Duff’s Ditch, in the Flood of 1997. Image Credit: Robert Linsdell on Flickr, unedited.


If you know your residence lies in a flood plain or you live near a waterbody, there are some things you can do to mitigate the impacts of flooding. Floods are unpredictable and they can happen in all corners of our country. The Canadian government has suggestions you can read up on, on what to do before, during and after a flood event to ensure safety. Some examples of things you can do prior to a flood:

  • Be sure the windows at ground level have waterproof seals.
  • Have downspout drainage installed a sufficient distance from your house so water flows away from the structure.
  • Store important documents in a waterproof container and on high ground.
  • Consider investing in a sump pump with zero reverse flow valves which can pump the water out of your basement.
  • Have an emergency bag ready to go with some clothes, provisions, essential medications, etc. if you need to evacuate your home.
  • If you have livestock, know the best way to leave them in flood conditions and make the necessary design changes to your structures to ensure the safety of your animals. 


Seeking out your provincial and local flooding guidelines is also important, as there may be specific instructions for your area. The prairie provincial flood information websites are linked here: Manitoba, Alberta, Saskatchewan


Understanding common flood conditions and educating yourself on best practices for before, during, and after a flood can help you prepare for when the unexpected happens. Flood events are severe and life-changing, taking a physical and mental toll on individuals, but with proper flood preparation negative impacts can be reduced. Water is essential for life but also has the ability to be extremely dangerous and unpredictable, it’s best to always be prepared.



Banner photo credit: Terima Kasih 0 via Pixabay


  1. Bridge Dale

    Rachel, the information about flooding that you’ve shared here is excellent, and I’ll utilize this information in one of my projects now. That is the best thing for me, and I am quite happy about this now.

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