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Stormwater system

The City’s stormwater drainage system is designed to collect stormwater from private and public properties across the city. The City maintains a network of culverts, storm sewer pipes and municipal drains that transport stormwater to nearby creeks.

The system helps to protect water quality and lowers the risk of flooding that can damage property and the environment.

A diagram showing pipes beneath a house. The foundation drain and sanitary connection connect to the sanitary sewer, which goes to waste water treatment facility. The catch basin between the house and the road connects to the storm drain, which connects to the storm outfall and Lake Ontario.

To keep this system working, the City invests in programs and infrastructure funded through the stormwater charge.

At an estimated 2017 replacement value of $2.06 billion, the stormwater drainage system is the second largest asset owned and operated by the City.

In Mississauga, the stormwater system includes:

  • More than 2,100 km of storm sewer pipes. If laid out end-to-end these pipes would connect Mississauga to the territory of Nunavut.
  • Over 51,000 catch basins, 278 km of ditches, 32 creeks and 62 stormwater management facilities that help to collect and drain the City’s rain water runoff before it enters Lake Ontario

Rain and melted snow from your property drains into ditches and catchbasins which flow to underground pipes, engineered ponds, and outlet to our creeks and the Credit River. Eventually this water makes its way directly into Lake Ontario, which is our source of drinking water.

Minor drainage system

During smaller storms, rain on the road drains into curb and gutter catchbasins or ditches and into the underground pipe system.

Major drainage system

During large, intense storms the road surface itself is also designed to collect and move stormwater to a safe outlet. This system also includes pathways and park spaces to take the stormwater from the road toward a pond or creek. This lowers the risk of flooding to homes and other properties.

City infrastructure and climate change

A lot of the City’s stormwater infrastructure was built in the 1970s and was designed based on historic rainfall patterns. Changes to our climate can bring intense rainfall and rapidly melting snow. Mississauga is also an ever growing city. To cope with these changes, Mississauga is working to increase the resiliency of the stormwater system with enhanced programs and implementing new practices such as green infrastructure.

Combining existing infrastructure with the benefits of green infrastructure

Traditional stormwater infrastructure is typically termed “grey” infrastructure. This may include underground concrete pipe systems, concrete outfalls, concrete catchbasins, engineered ponds.

Contemporary “green” infrastructure can also include new material types, native plants, trees, rain gardens and constructed wetlands that help to soak up rainwater and also reduce the amount of stormwater entering the pipe system.

Leveraging the benefits of both grey and green infrastructure improves the sustainability of the whole system and increases our resilience to climate change.

The City strives to reduce the impacts of pollution on stormwater using practices, tools and technologies like the following:

Catchbasins

Storm sewer catchbasins are sometimes marked with a fish to remind people that stormwater makes its way into nearby waterways. They’re designed to capture heavy debris and grit which is pumped out regularly.

Bioswales

Vegetated, shallow, open channels designed to carry and runoff and trap some pollutants in stormwater runoff, particularly from roadway drainage. They slow the flow of stormwater allowing time for some filtration of the water.

Oil-grit separators

An oil-grit separator is an underground device that uses separate chambers to remove coarse sediments (grit), oils and other buoyant pollutants (floatables).

Street cleaning

Streets are a significant contributor of pollutants to urban runoff. At regular intervals, the City clears sand and debris left behind on roads, sidewalks, and other areas.

Learn more about the City’s spring cleanup and street cleaning programs.

Salt management plan

During the winter, the City manages the use of salt on public roads and parking lots. In addition to the City’s plan, key staff are also certified in the Smart About Salt Program.

Learn more about snow clearing.

Sampling and inspection programs

City staff inspect discharge points from the storm sewer system to the natural environment on a regular basis. If a discharge is discovered that is not simply rain water or snow melt an investigation is undertaken to find the source. Sampling programs, laboratory analysis, closed captioned television technology and site inspections are used to find and eliminate the pollution source.

The city also implements special Low Impact Development (LID) measures to treat and/or control stormwater before it flows into the natural environment. These measures include:

Biofilters

A biofilter uses special soils and native plants to help filter out sediment and nutrient material. As stormwater passes through the soil and plants, some pollutants are removed.

Underground storage tanks

Underground storage tanks help control the flow of stormwater and aid in preventing flooding and erosion. Some special underground tanks also allow water to soak into the subsoil to control flows.

Stormwater ponds

Stormwater ponds receive stormwater runoff and allow solids to settle to the bottom. The ponds in Mississauga are designed to control flow and the amount of water that’s released to creeks. These are different from chemical treatment facilities that treat our water and wastewater.

You should never swim, wade, boat, walk or skate on stormwater management ponds. The water levels can change very rapidly and they can become quite dangerous. During the winter, ice on these facilities is weak due to water currents.

There are two main types of stormwater ponds in Mississauga:

Dry ponds

These types of ponds are designed to be dry most of the time and temporarily detain water. This helps prevent overloading the storm sewer system during large storms. These are often created as depressions in parks or next to roadways. The City currently maintains eleven dry ponds across Mississauga.

Wet ponds

Water levels in wet ponds rise and fall with each storm to help control the flow of water from rainstorms into local creeks. They have a designed normal water level and may include engineered wetland features. These types of ponds mimic the processes of natural lakes, and can have their own ecosystems including native species of mammals, fish, insects, turtles, frogs and birds. The City currently maintains 39 wet ponds.