How we’re monitoring stormwater

LID along the side of a road

Have you ever wondered what happens to rainwater when it drains into storm sewers? From a storm sewer, it flows directly into our local streams. Once rainwater hits the ground, we refer to it as stormwater in urban areas.

Traditional stormwater management focused on removing water as quickly as possible, without any treatment of the pollutants that stormwater collects on its way to drains and sewers. In urban areas, stormwater management is important for the health of the local environment. Municipalities are looking for ways to treat stormwater and remove pollutants before it enters local waterways and Lake Ontario.

A storm sewer along the side of a road.

An innovative approach to stormwater management is to retrofit existing areas with low impact development (LID), also known as green infrastructure. This approach provides opportunities to remove pollutants by slowing down rainwater, letting it soak into LID systems to filter pollutants as close as possible to where it falls. Examples of LID include permeable pavement and bioswales. Bioswales are depressed areas with plants or grass on the surface and with engineered soil underground designed to temporarily store and filter stormwater.

What do we do?

In 2014, CVC developed the multi-year Infrastructure Performance and Risk Assessment (IPRA) program to collect detailed information to evaluate LID performance in various land use types, designs and climate conditions.  

Monitoring helps us ensure that LID works properly even after several years of operation. It also informs maintenance needs and how often LID systems need to be inspected to avoid costly repairs. The data we collect is used by our municipal partners to plan future LID systems.

How do we do it?

We partnered with the City of Mississauga to monitor and evaluate the performance of bioswales and permeable pavement sties. We continuously monitor water levels and test how quickly water is going into the system, known as the infiltration rate.  This tells us how the bioswale overflows. This is important because if it overflows too often, we know it’s not working properly. Using precipitation data, we can see how the bioswale performs during different types of storms.

Permeable Pavers: an alternative to traditional asphalt this LID allows rainfall and road runoff to be filtered as it flowers through the pavers and returns to the ground. 
Boulevard Bioretention Units: the bioretention units, located in the boulevard, absorb and filter rainfall and road runoff as the water flows through the plants and soils and back into the ground.
naturally clean water
curb cuts: street runoff enters bioretention units through the curb cuts.
This figure shows a bioswale with soil and flowers. Water or runoff from the street enters the bioswale through a curb cut and is filtered through the soil.

Performance monitoring also helps us know if bioswales fill with sediment. Over time, sediment (fine particles such as dirt and clay) may start to clog, slowing down the infiltration rate. Testing every few years ensures the bioswale can still perform as expected.

Learn more about stormwater and LID performance monitoring by checking out our lessons learned.

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