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Flooding in Calgary: Understanding flooding

River 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 river flooding. Historically, this is when we receive our largest rainfalls.

How does Calgary experience flooding?

We experience two types of flooding in Calgary.

  • River flooding:
    • Heavy rainfall in the mountains and foothills is the largest factor leading to river flooding in Calgary.
    • Heavy rainfall causes the water in rivers and streams to rise to levels higher than their banks.
    • Groundwater (or the water found under the earth’s surface in soil or between rocks) backs up into basements due to high river levels.
    • Ice jams (floating ice that becomes trapped and impacts the flow of a river) on rivers may cause higher river levels, overland flooding, or high groundwater.
  • Local stormwater flooding:
    • Severe thunderstorms cause localized flooding of streets and property.
    • Snowmelt pools when catch basin drains (or storm drains) are blocked with snow and ice.
    • Stormwater or sewage pipes are overloaded or break, causing backup.

Flooding and Calgary’s river systems

The land where the Bow and Elbow rivers meet was where Calgary first established itself as a community.

The Bow River has a large watershed drainage area of 8000 km², but it also drops from the mountains to the city at a steep slope.

The Elbow River has a smaller watershed drainage area of 1200 km² and also drops from the mountains to the city at a steep slope. This means that, for river water in the Elbow, it is a relatively short, steep trip from the mountains to where it meets the Bow River in the heart of Calgary.

Having two short and steep rivers means that rising river levels can reach Calgary quickly and often with very little warning.

Flooding and Calgary's weather systems

Weather conditions in Calgary are also known to change rapidly. Being so close to the Rocky Mountains can make accurate weather forecasting a challenge. Weather forecasters often have a tough time predicting how weather systems will behave once they reach the mountains.

Generally, winter storms follow a more predictable pattern. This provides more warning time so that you can prepare and take appropriate actions.

Summer weather patterns are much more unpredictable. When you are monitoring the weather, you may also hear alerts or advisories related to the Bow or Elbow rivers.

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.

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.


Videos

Understand: River Flooding