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Understanding river flow rates

Learning about river flows is the first step to understanding rivers in and around Calgary, and improving flood resiliency in our communities.

What is river flow?

At its most basic, flow is a measure of the amount of something travelling past a point in a given amount of time. In rivers, the flow of water is typically reported in cubic metres per second. A cubic metre of water is what you’d get if you built a box one metre high, one metre wide, and one metre deep, and filled it with water. That’s the same volume as 1000 litres and it weighs a metric tonne.

When flow increases in a river, there’s nothing to constrain the water. This means increased flows can result in higher water levels, faster moving water, or a combination of both.

Most of the time a river is large enough to contain its flow, and water stays inside its banks. But if flows are large enough, the river can’t hold everything and water escapes the banks and starts flowing over normally dry land and through the floodplain.

River flows are evaluated by our Flood Monitoring Team year-round, but especially during flood season which runs May 15 to July 15 each year.



Bow River Triggers - Upstream of where the Bow River meets the Elbow River

Flow rate (m3/s) ​Chance of occurring in any given year ​Effect
250 m3/s
70 - 400
Normal seasonal river flow
(approximately May 15 to July)
​> 50% ​Riverside pathways impacted
550 m3/s
401-708
Higher than normal seasonal river flow
50% ​Heritage Drive/Glenmore Trail underpass inundated with water
927 m3/s
700
Flow in excess of channel capacity
​12% Overbank flooding may reach some homes
Evacuation may begin (potentially Bowness, Sunnyside and Hillhurst)
Temporary barrier construction is triggered
Prince's Island inundated with water

Elbow River Triggers - Downstream of Glenmore Reservoir

Flow rate (m3/s) ​Chance of occurring in any given year ​Effect
40 m3/s
< 30 - 90
Normal seasonal river flow
(approximately May 15 to July)
> 50% ​Riverside pathways impacted
120 m3/s
90 - 170
Higher than normal seasonal river flow
29% ​Modest overbank flooding occurs in mostly unpopulated areas
275 m3/s
170
Flow in excess of channel capacity
​5% Widespread evacuation
Significant construction of temporary barriers

To see river flow data from previous years, visit historical river flow data in The City of Calgary.

River Warnings and Advisories

If necessary, the Government of Alberta may issue a warning or advisory based on the current river flow. To see the latest warnings, notices and advisories visit current river advisories and warnings.

High stream-flow advisory
This means that stream levels are rising or expected to rise rapidly. No major flooding is expected, but minor flooding in low-lying areas is possible. If you are using an affected river or are located close to an affected river (camping, fishing, boating etc.), be cautious of the rising levels.

Flood watch
A flood watch means that stream levels are rising and will approach or may exceed the tops of river banks.

Flood warning
Flood of areas next to rivers under a flood watch may occur, and you are advised to take appropriate precautionary measures as instructed by the authorities.

Weather warnings and advisories

Weather advisory
An alert issued by Environment Canada when a certain weather or environmental hazard is either occurring, imminent or expected to occur. Pay attention for further information on the potential weather event.

Weather watch
A watch is issued when conditions are favourable for the development of a weather or environmental hazard that may post a significant threat to public safety and property. Continue to monitor weather conditions and take appropriate precautions.

Weather warning
A warning is an urgent message issued when a hazardous weather or environmental event that poses a significant threat to public safety and property is certain or imminent. Seek appropriate shelter and continue to monitor conditions. For more information, visit Weather Canada.

State of local emergency
If there is danger to life, great widespread risk to public and private property, or if there is a need to consolidate resources, The City of Calgary officials can declare a Local State of Emergency.

This gives the Director of Emergency Management special powers to take measures to protect life and property, including ordering mandatory evacuations. A State of Local Emergency has happened twice in Calgary - 2005 and 2013.