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Flooding in Calgary: Understanding flooding

Flooding can occur at any time in Calgary, although the period between May 15 and July 15 is when we are most likely to experience flooding. Historically, this is when we receive our largest widespread rainfalls.

How does Calgary experience flooding?

Flooding in Calgary can happen in several ways:

  • Rivers and streams cannot contain excessive rainfall within their banks.
  • Rain and snowmelt cannot be absorbed into the ground.
  • Waterways or storm drains become blocked with debris or ice.
  • Water containment systems, such as stormwater or sewage pipes, are overloaded or break, causing backup.
  • Severe thunderstorms cause localized flooding of streets and property.
  • Ice jams on rivers may cause elevated water levels and overland flooding.

Flooding and Calgary's water systems

Calgary sits at the confluence of two small rivers, the Bow River and the Elbow River, and several smaller creeks.

The Bow River has a large watershed drainage area and drops from the mountains to the city at a steep slope.

The Elbow River also drops in elevation at a steep slope and so it is a relatively short trip from the mountains to where it meets with the Bow River in the heart of Calgary.

Having two short and steep river systems means that fast changes to high flow rates can reach Calgary rapidly with little warning.

Flooding and Calgary's weather systems

Weather conditions can also change rapidly. Calgary’s proximity to the Rocky Mountains makes accurate weather forecasting a challenge.

Weather forecasters have a tough time predicting how weather systems will behave once they reach conditions surrounding the mountains.

Generally, winter storms follow a more predictable pattern, allowing more advance warning time so that you can take appropriate actions.

Summer weather patterns can be much more unpredictable. When you are monitoring the weather, you may also hear alerts or advisories related to the river.

If you live in the floodplain or in low-lying areas, it’s important to understand what the alerts mean so you can be prepared and take action.

Understanding flooding - information and resources

Types of flooding
Learn more about the types of flooding that can happen in your community.

River flow rates
Learn more about what triggers impact river flows for the Elbow River and Bow River, as well as, the common warnings and alerts related to Calgary river conditions.

Flood monitoring
See how our team of river engineers keeps a watchful eye on Calgary's watersheds.