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Storm drainage system - FAQ


Below you will find common questions about Calgary's storm drainage system. For issues or questions about storm drains (or catch basins), please visit our Storm Drains page.

Storm system background

1. How is the storm drainage system built?

In most communities in Calgary and other cities, the underground storm-drainage pipes are designed to meet the North American standard of draining one-in-five-year storms.

To put this in perspective, in Calgary, 2.54 cm (1 inch) of rainfall in one hour is considered a one-in-five-year storm. A storm-drainage system that is designed for one-in-five-year rainfalls can handle 80 per cent of the storms.

In some older communities, the storm-drainage systems are designed to handle one-in-two-year rainfalls. All the communities built in the 1990s and after, have a system of underground pipes that can handle one-in-five-year rainfalls and a system of specially designed streets and storage ponds that, by storing water temporarily, can handle one-in-one-hundred-year rainfalls.

This overland system is necessary, because the underground storm drains in some areas would have to wider than the streets under which they are buried, which would be impractical and extremely expensive.

Due to physical constraints in developed communities, it is not always possible to design improvement projects that will increase the capacity of the storm-drainage systems to handle one-in-one-hundred-year rainfalls.

For more background information on how Calgary's storm system infrastructure was built, please visit History of Stormwater Management in Calgary.

2. Why does water collect in front of my house when it rains?

The drainage systems in newer communities are designed to protect homes from flooding by storing water on the streets at a safe level.

When rainfall exceeds the capacity of the underground pipes, a device inside the storm drains prevents water from entering. When the pipes can handle more water this device will allow water on the street to drain at a controlled rate.

For issues or questions about storm drains, please visit our Storm Drains page.

3. What is The City doing about algae in storm ponds?

The City of Calgary will be testing various algae control technologies in select storm ponds from 2016 to 2018, June through August. It will determine the most cost effective means to maintain Calgary's storm water ponds.

To learn more about this three year project, visit our algae control storm pond page.

4. What are dry and wet storm ponds?

Storm Pond Infographic

What is a Storm Pond?
Click for larger image.

Calgary's storm-drainage system has over 150 storage ponds. They hold water that exceeds the capacity of the underground storm-drainage pipes. .

Dry ponds hold water that is handled by the storm drainage system. Wet ponds handle excess water and improve its quality by removing solids through sedimentation.

Almost all the dry ponds have ultrasonic sensors that record water depths. The sensors also inform us when the ponds are filling with water. To protect citizens from the possibility of drowning in dry ponds, these ponds do the following:

  • Fill and drain slowly
  • Have gentle slopes at the edges
  • Use signs to warn people about flooding during rain
  • Use alarms to alert us that the ponds are filling
  • Are inspected by security guards during rain storms

The other ponds are storm ponds because they hold water all the time. Typically they are designed with normal water depths of three metres. These ponds can dry out in the summer although normally they keep their base all year.

The wet ponds have a continuous flow of water that provides movement through the ponds. The combination of the movement and depth prevent mosquitoes from forming.

We alsoprovide measures for dealing with beaver habitats in parks. If you notice beaver activity in a wet pond, please call 311.

If the pond is located in an existing off-leash area or park, then off-leash dogs are allowed to access the wetpond. For all other parks or areas, off-leash access is not allowed. In general, we caution against anyone or their pets coming into contact with the water in any wet pond for safety and water quality concerns.

5. What do the stormwater gates on the river do?

In winter, ice can build up and force water from the river, and into the storm mains and surrounding communities. The gates prevent this from happening. The gates are closed and monitored daily during winter months (November to April) because the ice pack on the river can change dramatically in a short period of time.

If the level of stormwater is significant, the gates are opened and the water is released. The gates are then immediately closed again. During summer months (May to October), the gates are fully open; however, they are monitored during this time and closed during high river flows to prevent water flowing back into the community.

6. How is the storm drainage system financed?

Since January 2004, the storm drainage system became self-supporting through what is now called the monthly Drainage Service Charge on customers' utility bills. Like the water and wastewater utilities, the storm drainage system does not receive money from property taxes.

Storm drainage system costs include capital projects, retrofits, upgrades, operations, monitoring, regulatory reporting, and the maintenance of over 160 (wet and dry) ponds, almost 4,000 kilometres of pipe and over 800 outfalls.

Storm system and flooding

1. What does The City do about flooding?

We evaluate potential storm sewer system improvement projects in communities subject to flooding before every construction season. Evaluations are based on these safety considerations: amount of flood damage, number of floods in each area, and design and cost-effectiveness of the project. These projects are funded by the drainage charge on your monthly utility statement.

We are also working in other ways to keep Calgary flood prepared. See a list of the preparation steps and mitigitation measures we're taking on our Flooding in Calgary site.

2. How can I protect my home from flooding?

There are a number of steps you can take before, during and after flooding. Visit our Flooding in Calgary site to learn how to assess your flood risk, and how to prepare your home, property or business for flooding.