Rivière St. Pierre, Part V: Ovalflow
Following Rivière St Pierre as it makes its way through the village of Rockfield and (sometimes) into the Lachine Canal
Picking up from where we last left off, this stretch takes us through the inside of the Cote-St-Luc collector sewer at the northern edge of Lachine. From here it snakes its way southwards towards the Lachine canal, never straying too far from the original course of Riviere St. Pierre. Approximate round-travel distance: 4 kilometers.
I never look forward to having to cover larger distances inside sewers here in Montreal. The depth will vary, but 2-3 feet tends to be the norm. That might not seem like a lot, but when you factor in the speed at which it’s flowing and the amount of gear these types of trips can entail, it doesn’t take long before it starts to feel like a solid cardiovascular workout. This is especially true when you’re walking against the flow.
Here’s a general overview showing the CSL collector (the dark red line), the estimated path of Riviere St. Pierre and a few of the features described below.
For the first kilometer and a half, this portion of CSL collector is pretty straightforward: 8×10 feet in diameter with a shape that’s typical of concrete sewers built in Montreal between the 1920s and 1970s. A smooth horseshoe-shaped arch covers a course aggregate floor that that slopes towards the edges. During dry weather, the edges of these types of sewers are usually dry. City plans define this section the “sidewalk”; but that term’s a bit misleading. Due to the angle, it’s actually terrible to have to walk on.
Because of the broader arc of the sewer and for some of the features described below, I decided to name this length of the CSL Collector “Ovalflow.”
It’s unclear when the sewer replaced this portion of Riviere St. Pierre. While bits and pieces seem to have been covered as early as the 1930s, I suspect everything was eventually reconstructed during the mid-1960s when the entire area’s sewers were integrated into a much broader system.
By the time the sewer reaches the area of Lachine known as Rockfield, things start to get a bit more interesting.
At this point the CSL collector officially comes to an end inside a rather unusual chamber containing a number of interesting features. As seen in the photo above, on one side of the channel are four cells. All the water flows into the cell closest to the camera at which point it falls down a sinkhole into an even larger sewer- the appropriately named St-Pierre Collector, which we’ll get to in future entries.
The other three cells contain a metal cylindrical object suspended directly above a three-foot wide hole, one of which is entirely blocked up with sludge. Above these are a number of counterweights and a mechanism (shown here) likely designed to lower each cylinder so that it covers the hole. Since each hole seems to lead to the same sewer further below, I’m not sure what purpose these things actually serve. A water monitoring device (or flowmeter) sits high in one corner of the chamber, but it’s unknown if it has any connection to the large plugs or if it simply sends an alert whenever water levels start to rise.
Also found in this chamber is the beginning of a rectangular shaped conduit situated roughly eight feet above the main channel of the sewer. The principle here is simple: when the water inside the sewer reaches a certain height, the surplus flow is diverted through this tunnel and out into the open water- in this case, the Lachine Canal.
This is one of the drawbacks of a combined sewer system. Most of the time everything gets sent off to the treatment plant as intended, but during heavy rainstorms, the system can become overburdened to the point where sewage spills out into the open water. Fortunately, these events only seem to happen a few times a year, but they’re still a source of significant water contamination. If you’ve been warned not to swim in the Lachine Canal (or elsewhere on the island), combined sewer overflow events are likely the reason why.
This eleven by five foot high conduit (known as the Rockfield Overflow) runs for a quarter of a kilometer, but because the outfall at the canal is submerged, one can only travel about two thirds that distance. Any further and you’re soon up to your chest in canal water.
At this point your only choice is to turn around.
Other Articles
Following Rivière St. Pierre
A five-part series following the Western reaches of Montreal's most famous lost river
Rivière St. Pierre, Part II - Double Ducker
Following the water of St Pierre River from its last remaining stretch aboveground down into the sewers
Rivière St. Pierre, Part III - Slips and Slides
Taking tumbles while following the subterranean slopes of Rivière St. Pierre
Rivière St. Pierre, Part IV: Deep Breath
Following Rivière St. Pierre through the sewers beneath the sleepy suburb of Cote St. LucThere are 7 comments
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Un article si bien écrit en effet; merci! J'apprécie le développement de la réalité géographique en parallèle aux doutes faisant presque office d'éducation méthodologique. Quelle […]
Amazing article, I am glad it worked out for you!
I happen to live near a 1/4 km section of creek in the Valois area of Pointe Claire. As far as I can tell, […]
Cool, cool. As always it’s great to get hear more detail of how the system is set up and where it runs etc. That first Rockfield chamber pic is a beaut and the city plan is a nice touch, where’d you dig that up?
Fantastic! Your photos are incredible, and your commentary and explanations are educational and enjoyable. I can hardly wait until the next “exploration”.
Thanks! Jondoe: the map came from the city planning department. It’s relatively easy to get whatever you want. You just have to pay a small fee and they’ll scan or print whatever you want.
Good job again micro . Nice infos about the system and your pictures are great !
Wow, this is amazing (I just got through all 5 posts). Excuse my naivete, but is it legal for people to walk through city sewerage systems? How often is municipal staff around?
Thanks for these and keep them coming!
Amazing! Great pictures! I used to work at the Nortel (Northern Electric) Plant on the Hwy 20. A friend of mine took me into the entrance of the St. Pierre river under the plant around 1988, until then I had no idea that it existed. He told me that alot of companies had access to the river and used to dump industrial waste into it, that’s why the lachine canal never froze over in winter. I’ve told alot of people about this and most just said he was pulling my leg! Thanks for vindicating me!!
You made my day! I saw you on TV …That’s why i’m here. I know where the outfall is in the canal and it’s not submerged at this time of year and it ends with a double ducker…i always wondered where it would take me if i was crazy enough to go up there. Now i know. Thank you for sharing! What an amazing adventure it must have been.