Flooding, erosion and the power of water


Floods come in different varieties. This past Tuesday night in Toronto, heavy rains caused flash flooding across the city. Police even had to rescue two men trapped in an elevator. While Mississauga missed the worst of this recent storm, this past February saw a different sort of flood near CVC’s head office in Meadowvale Conservation Area.

In summer, short, intense storms can drop so much rain that storm sewers are overwhelmed, causing rainfall to puddle, pond and then flood low-lying areas. In  winter, storms are less intense. They usually take longer to drop the same amount of rain as summer storms. However, other factors can add up to flooding events in the winter months.

On February 21, temperatures were just right for ice to break up and to jam at bridges and other narrow points across the Credit River Watershed. Snow was melting quickly as well. So, when the rain started falling, water levels in the river started rising. This storm produced a lot of rain: at CVC’s nearby rain gauge, it measured as a one-in-one-hundred year storm. And when all that water ran into an ice jam in the Meadowvale Conservation Area, it was left with nowhere to go, except to leave the riverbed and rush through the conservation area. The result was significant erosion.

Rushing water dug out a deep channel along a footpath at Meadowvale Conservation Area.

The erosion of river banks occurs both naturally and through human impact. Rivers are dynamic and their shape is regularly changing. Riverbank erosion can produce favorable outcomes such as forming habitat aquatic life. Some rivers have a healthy amount of erosion.  But in urban areas river erosion may be excessive due the increased amount of concrete, destruction of wetlands and lack of stormwater management. Erosion can become an issue when rivers approach infrastructure near or next to the river and poses a danger to people and property.  Not all erosion needs fixing.  If erosion is excessive threatens people or property it can be very expensive to fix.

Fixed Erosion
The same pathway after the City of Mississauga fixed it.

We work with our municipal partners to prevent unwanted erosion and its associated costs. The key to reducing erosion is slowing down stormwater runoff before it reaches streams and steep slopes. One way to do this is by designing stormwater features that promote infiltration (when water seeps into the soil).

For example, our low impact development project at Elm Drive in Mississauga replaced an old ditch and sidewalk. The specialized design, soils, plants and pavers help stormwater runoff infiltrate into the ground, filtering out pollutants from the water. This limits the amount of water flowing through the storm sewer system and into Cooksville Creek, which is known to have erosion issues.

Low impact development feature at Elm Drive in Mississauga
The low impact development feature at Elm Drive in Mississauga allows stormwater runoff to infiltrate into the ground.

Learn more about low impact development and how it can help us tackle flooding and erosion.

Comments (1)

  1. Another way to prevent erosion and flooding is to protect and restore natural features on the landscape – such as wetlands, woodlands, floodplains and valleylands. Natural vegetation in these features absorbs and slowly releases water, protecting downstream areas from flooding.

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