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Understanding Drainage

Understanding how water drains

Drainage removes water from an area. Proper drainage makes sure that water flows away from the walls of your home or building. It can help reduce the risk of flooding, damage, erosion or wet areas.

Roadside drainage

City roads are built with the centre higher than the sides. This design, called crowning, forces stormwater to flow to either side of the road into ditches or curb and gutter drains, to collect the stormwater. These collection systems work in different ways.

Traditional Ditches:

  • Can be found in older areas of the city
  • Are dips in the land alongside a road, below road level
  • Move water to storm drain inlets at a low point
  • Allow some stormwater to soak into the earth
  • Collect property drainage (from driveways, sidewalks and surrounding lands)
  • Store snow in winter

Curb and Gutter Drains:

  • Can be found on most city streets
  • Trap water in the gutter using concrete curbs
  • Move water into nearby catchbasin
  • Collect property and lot drainage from hard surfaces

Roof Eavestroughs and Downspouts

Eavestroughs collect water from your roof during rainstorms and direct the water to downspouts leading down the wall to either an underground drainage connection to the city’s storm drainage system or to a safe discharge point two (2) metres away from your foundation. Eavestroughs and downspouts should always be inspected and any leaves or debris should be removed to ensure that blockages do not lead to water build-up next to basement walls.

Drainage swales

Drainage swales are gently sloping, V-shaped, shallow grassy ditches often found along property lines between houses. They direct stormwater away from areas like the foundation of your property and your yard towards a safe outlet like a street drain or catchbasin inlet.

Drainage swales do not work if they are blocked. A swale will help protect your foundation and filling one in can result in ponding and risk of flooding. They should never be filled in without first ensuring that the water drained by the original swale goes away from the house in another way.

Why is there a catchbasin in my yard?

A catchbasin may be found in the grass at the lowest point of a homeowner's yard so water can flow away from that property and from neighbouring properties to prevent flooding.

Backyard catchbasin inlets must be kept clear to allow stormwater to drain safely. Property owners with a catchbasin are responsible for keeping the catchbasin drain clear of blockages.

Climate change and drainage

Much of Mississauga’s stormwater infrastructure was placed in the last 50 years and was designed based on historic rainfall patterns. Changes to our climate can bring heavier rainfalls and rapidly melting snow. Most of the City's infrastructure has a service lifespan of 100 years.

To properly maintain the City’s existing stormwater infrastructure and cope with more frequent and heavier rainfalls, we need to use more “green infrastructure" such as trees, rain gardens and wetlands to soak more water into the soil. Green infrastructure soaks up rainwater and reduces the amount of stormwater entering the pipe system. Plants and soil filter pollutants and soak up water, improving the quality of stormwater flowing to Lake Ontario where we get our drinking water.

While all infrastructure requires maintenance, the gardens, trees and plants maintain their effectiveness as they grow larger and become more attractive.

Keeping water out of the pipe system also helps to save money on costly construction upgrades and repairs, protects properties and makes our city beautiful.

Drainage systems for small and large storms

  • Minor Drainage System: During small, low-intensity storms, stormwater that falls on roads will move into curb and gutter catchbasins or ditches and into the underground pipe system.
  • Major Drainage System: During large, high-volume storms where ditch, roadway storage, catchbasin and stormwater pipe capacities are exceeded, the road surface is designed to 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, minimizing the risk of impacts to homes and other property.