Garrison Creek West Branch Storm Trunk Relief Sewer
Garrison Creek Sewershed
Western Beaches Storage Tunnel
Year of Construction:
Tunnel-excavated, round concrete lining (2550mm and smaller)
Also Known As:
Cowan Avenue Storm Sewer
Pilgrimage was the first part of the Garrison sewershed that myself and my colleagues found ourselves inside, though at the time we had no idea that these were related at all. We were looking for ways to reach the Western Beaches Storage Tunnel (WBST, an objective that remains unfulfilled), and the storm sewer connection at Cowan Avenue was the first WBST connection we found access to. Yet any dreams of reaching the three-meter wide interceptor and its set of giant storage tanks along the lake were quickly dispelled when we headed down the pipe towards the lakeshore rail corridor and discovered that it ended at a flooded siphon. Turning our attention to the system itself, we headed upstream to a long walk and a few fascinating bits of architecture, including the incredible wall for which we named the system "Pilgrimage."
The Cowan Avenue Storm Sewer, or the "West Branch of the Garrison Creek Storm Trunk Relief Sewer" (the impossible name used to describe it during its construction), begins at Davenport Road and flows in a southwest direction through Dovercourt Village and Bloorcourt, Dufferin Grove, Brockton Village and Parkdale to an original outfall south of Cowan Avenue. With the c. 2000 construction of the WBST, stormwater and combined sewage overflows from the western portion of the Garrison watershed now enter the storage tunnel and are conveyed to the foot of Strachan Avenue, where solids are pumped back up to the city's interceptor network and liquids receive UV treatment before being released into the lake.
The West Branch storm trunk relief sewer was one of the first part of a 25-year programme of sewer remediation and expansion that the City of Toronto embarked upon in the 1960s under then-Commissioner of Public Works R.M. Bremner (for whom Bremner Boulevard, near the CN Tower, is named). Authorized before that programme was officially adopted, the storm sewer was completed by 1965, and has facilitated partial sewer separation (where roadside storm sewers are disconnected from the old combined sewer network) in the west end. However, a number of chambers remain where western tributary sewers of the Garrison system, like the Denison Stream sewer and the more southerly tributary that runs down through the Osler and McCormack Playgrounds, can overflow into the storm relief, and they still do so regularly during storm events.
Slung off the side of the main Pilgrimage conduit and up twenty foot access shafts, these overflow chambers were a surprise to us. Unlike other overflow structures I've seen that use some form of weir where a high-flowing sewer crests over the side of the wall and into the overflow sewer, in two of the Pilgrimage overflows a whole chamber is provided, through which the overflow sewer runs in an open trench. It's a messy arrangement (as the cresting sewer simply overflows into the room, and from there down the same shaft that provides physical access to the relief tunnel) but an exciting one. The chambers also include control gates that must be raised and lowered manually.
At Bloor Street, Pilgrimage must negotiate the underground barrier of the Bloor-Danforth subway line, which was built at roughly the same time that the storm relief sewer was installed. North of the subway, the storm relief runs just below the surface, and was probably installed in a cut-and-cover fashion, unlike the rest of the system to the south, which is much deeper and would have been mined. The transition between these two depths is abrupt, and occurs directly south of the subway line between Dufferin and Ossington stations. Walking up the sewer, after a series of bends one is confronted with a massive wall, fronted by a splash pad and small weir. In dry weather, the small amount of flow in the sewer is diverted through a small penstock behind the wall and flows out uneventfully at its base. In wet weather, Dovercourt Village's rain and overflowing combined sewage (if there is a northern overflow near Dupont Street, I haven't gone back to check) would come straight down over this wall in a furious torrent.
Deep but not too deep, in some ways Pilgrimage is the most urban-feeling of the west end's large sewers. Walking its length, sounds and smells filter down from the streets above, reminders of the life facilitated by the Garrison sewershed: the woosh and rumble of streetcars passing on King, Queen, Dundas and College; occasional whiffs of gasoline and car exhaust (and of course our periodic confrontations with the fresh smell of the combined sewers that Pilgrimage relieves); and occasional and far-off fragments of exhuberant nighttime conversation. Outside of our very rare visit, these are experiences left only to the handful of rats that somehow subsist in the relief conduit, making apartments in the overflow shafts and witnessing the fleeting evidence of the city above.
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.