Side connection at Wolseley Street, beneath Denison Avenue, in the Garrison East Branch Storm Trunk.

Measure of Emptiness

Garrison East Branch Storm Trunk Sewer

Garrison Creek Sewershed (East)
Russell Creek Watershed

Year of Construction:

Construction Details:
Deep, round tunnel excavated beneath existing streets and lined with concrete. Due to unfavourable geological conditions, some sections had to be mined in compressed air. The diameter of the tunnel is 3000 mm south of Bloor, and 3600-3750mm south of Dundas Street. Significant branches occur at Lowther Avenue and at Dundas Street.

Like Pilgrimage to the west, the Garrison Creek East Branch Storm Trunk Sewer was the product of a 25-year programme of sewer renewal initiated in 1965 by Commissioner of Works R.M. Bremner. Built to avoid a variety of existing underground infrastructure, the East Branch Storm Trunk is deeper than just about any other storm sewer in Toronto, running at a consistent depth several stories underground until it reaches the rail corridor south of Front Street. This deep geology complicated its construction -- downtown Toronto is built on top of an unstable collection of glacial tills, silts and sands -- forcing a series of delays as sections of the excavation had to be outfitted with airlocks and other necessary equipment for excavation in compressed air. 1

In Bremner's own words, the purpose of this storm trunk sewer was "to provide relief to the existing sewerage system which was built prior to the turn of the Century and no longer has the capacity to accomodate storm run-off conditions prevailing in the built-up City of the 1970's." 2 Built to the form of the street grid rather than any natural formations, the system bears little resemblance to the surface watershed it drains -- indeed, most of the sewershed isn't even part of the old Garrison Creek basin but rather the much less well known Russell Creek that once ran through the Annex and Kensington.

The East Branch Storm Trunk is probably the largest drain in the lower part of Toronto. Almost four metres in diameter as it approaches the old shoreline, it runs very deep and very dark. Having been mined rather than cut-and-covered, there are comparatively few access shafts. Even the concrete seems to be of a darker pigment than I've come to expect, making lighting photographs here difficult. At the bottom of Portland Avenue, a siphon takes the flow of the pipe to lake level and leads directly into the harbour, and dozens of fish congregate at the top of this murky, slot-shaped pool. The end of the conduit also features flow metering equipment and a pair of steel beams loosely placed across the pipe that may be an ersatz effort to warn visitors of the deep pool ahead.

  1. 1. R.M. Bremner. December 18, 1973. Report to Committee on Public Works. "Garrison Creek Storm Trunk System - East Branch." Department of Public Works, City of Toronto.
  2. 2. Bremner, 1973.
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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.