Building the Stormwater Master Plan

When rainwater hits the ground or when snow melts, it generates stormwater as it runs off the surface. Hard surfaces (e.g. asphalt, concrete) generate more stormwater than soft surfaces (e.g. grass), as stormwater cannot soak into the natural ground and flows off the land much more rapidly, increasing the potential to cause flooding and erosion.  Pollutants may also be carried by stormwater into the natural environment.

The Stormwater Master Plan aspires to build on the City’s existing stormwater management program of actions, based on municipal priorities and legislative requirements, and recommend improvements to existing actions and/or additional actions to effectively manage stormwater in Mississauga.

Managing the City’s stormwater is very important as all of the City’s rainwater and snowmelt ends up in Lake Ontario, which is the source of the City’s drinking water.

Stormwater management is crucial in protecting public safety and health, and works to reduce flood risks, control erosion and maintain water quality in local natural waterways. The City manages stormwater by planning, designing, constructing, operating and maintaining stormwater assets within municipal roadways, public easements and other City lands.

A Master Plan helps further refine and optimize the existing actions the City is taking to manage stormwater.

“Build” implies a proactive approach that meaningfully constructs the future we want for our City. “Beautiful” signifies the desire to have attractive built form that integrates with our natural environment to help make our communities livable and sustainable.

The Stormwater Program is the annual suite of projects and actions the City employs to manage stormwater. The Program is informed by best practices and experienced staff.

The Stormwater Master Plan is a higher-level document that plans longer-term, and will be used to refine the Stormwater Program based on a broader review.

• Erosion and sediment control
• Flood protection projects
• Maintenance and repairs to existing infrastructure
• Emergency response to flooding, spills and clean-up
• Street sweeping
• By-law enforcement to protect the environment and prevent interference with the operation of the stormwater management system

• Climate change is affecting the intensity and frequency of storm events that stormwater management programs must respond to.
• Urban growth and development alter the amount of runoff and pollution.
• Infrastructure such as pipes, culverts and outfalls have limited life expectancy.
• Stormwater facilities must be actively maintained throughout their expected life, including watercourses, storm sewers, catch basins, stormwater ponds, pump stations, culverts and outfalls.
• Appropriate resources, assets and improvement projects must be proactively planned to address needs and problems.
• Design standards have changed, and designs developed under older standards may be inadequate to meet regulatory requirements

These are most often structural measures that municipalities use to manage stormwater.  For example, the City may build a retention pond (i.e. “stormwater management facility”) to temporarily hold back water to reduce the impact of peak stormwater flows during heavy rain events.  The City may also use more sustainable measures like rain gardens to clean stormwater before it is released to creeks and watercourses.

In recent history, drinking water is seen as a highly valuable resource while wastewater and stormwater have often been considered as waste products to be managed and disposed of.  The term “One Water” emphasizes that water comes from one source, as our rainwater becomes stormwater and ends up in Lake Ontario, which is the source of our drinking water. Mississauga is fortunate to be located next to one of the largest freshwater resources on the planet, however it is important to remember that water is a scarce resource.  The “One Water” principle recognizes that all water (i.e. drinking water, wastewater and stormwater) is a resource to be valued.

River or Riverine flooding is associated with excessive rainfall or snowmelt that results in rivers exceeding their capacity, and water flows outside of the river banks.

Urban flooding is associated with excessive rainfall that cannot be absorbed into the ground and overwhelms the urban drainage system. For example, when there is more water than the sewers can convey this results in flooding on roadways.

The Climate Change Action Plan identifies actions that the City plans to accomplish within the next five to ten years to mitigate and adapt to climate change. This includes several stormwater management actions to support resilient and sustainable infrastructure, including the recommendation to develop a Stormwater Master Plan.