The City of Calgary's Ice Monitoring Program tracks weather and river ice conditions to assess the potential for ice-related water level hazards. This program is one of the ways our river team monitors water levels as part of the River Monitoring Program.
How the Ice Monitoring Program works
Monitoring water levels on the Bow River
Running from mid-December through March, the program allows The City to be response-ready for ice-related water level hazards.
These can include closing pathways and storm outfall gates, as well as issuing public safety warnings.
In Calgary, the issues we see with ice jams are generally on the Bow River.
The Elbow River and our creeks have minimal ice jam potential due to the low seasonal water flows. On the Bow River however, we normally see issues with ice jams when ice first forms, called "ice up".
We have water level monitoring equipment to help determine how the water level changes as the ice forms on the Bow River. Data from this equipment helps us refine the monitoring program for future years and helps with ice formation predictions.
What is the impact of ice jams?
In natural areas along the river, ice jams can cause damage to trees and shrubs and can even move soil and rocks along the riverbed and banks.
In urban areas where infrastructure is close to the river, smaller water level rises from ice jams can cause issues such as pathways flooding and backflow into our stormwater systems.
We guard against this by regularly checking our pathways, and closing areas that become flooded. We have also installed gates on lower-lying stormwater outfall pipes to safeguard against river water flowing back into pipes and onto streets.
Ice jams that cause larger water level increases can lead to groundwater seepage into buildings, especially those with deep foundations. For very large ice jams, which cause a significant rise in water level, the river can potentially spill over the banks.
How can ice jams impact my home?
The most common problem ice jams cause for homeowners is groundwater seepage into basements. Although we ensure our storm system is draining properly, private land owners need to have emergency response measures in place to prepare for groundwater seepage, such as sufficiently sized pumps.
For more information on handling basement seepage and preparing your home for flooding or seepage, visit Basement Flooding and Seepage, and Flood Readiness.
The science behind ice jams and "slurpees"
The three main factors affecting ice formation on the Bow River are the following:
- Ambient air temperature
- Distance on the river from Bearspaw Dam
- River channel slope
Calgary typically needs four or five days of extreme cold weather before river ice forms.
The water needs to cool a lot to start freezing, so zero Celcius or warmer water leaving Bearspaw Dam needs to travel some distance before it cools enough for ice to form.
The water in the river will cool as it moves over shallow, fast moving sections and frazil ice begins to form (globs of ice carried in the river - also know as the "slurpee").
As it moves downstream through Calgary, the river channel can eventually become bridged, which is where the ice covers the river from bank to bank. For most years, we see bridging start in the deep pool downstream of Cushing Bridge (17 Avenue SE).