One of two large stormwater detention ponds constructed between the ramps of the 427-409 highway junction


Highway 427-409 Storm Sewers and Detention Ponds

Mimico Creek Watershed
Highway 409 and 427 storm sewers and stormwater retention ponds

Construction Details:
Elliptical basins of gleaming white concrete fitted with weirs and outfall/inlet structures drain to a short tunnel with further connections to older Highway 409 storm sewers (RCPs)

The last decade saw the reconstruction of Highway 409, the short stretch of divided, multi-lane highway that connects Highways 401 and 427 with Toronto's Lester B. Pearson International Airport. It may have been during this rebuild, or sometime in the 1990s,  that two enormous stormwater detention ponds were built inside the interchange ramps at the 427-409 junction and additional tunnels added to the existing c. 1974 storm sewer that provides drainage for the portion of the 409 between the 427 and the bridge over Mimico Creek. Additional drains, as yet unexplored, probably feed from the western-most segment of the 409 into the west detention pond.

The ponds are certainly the most distinctive feature of this stormwater system. Providing some 10,000 m3 of storage capacity, their symmetry makes their appearance very distinctive from the air; as a result, my colleague who was the first of us to make the trek out to this difficult to reach location was moved to call the system "Vasectomy". The system outfalls on the north side of the 409, into a short channel that leads to Mimico Creek.

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Michael Cook is available to speak to your organization about infrastructure history, lost creeks, current conditions, and opportunities for change in our management of and communication about urban watersheds, and to work with teams proposing or implementing such change. Get in touch.