Pipe Dreams

An in-depth look into the extensive post-war sewer systems of Montreal’s suburbs. How the optimism of an era defined the scope of what’s found today

Inside the Decarie-Raimbault Collector Sewer.

Pipe Dreams

An in-depth look into the extensive post-war sewer systems of Montreal’s suburbs. How the optimism of an era defined the scope of what’s found today

For the past couple of years now, I’ve been looking for ways to get inside the sewers found within a northern portion of the island of Montreal. Actually, that statement is a bit misleading since it hasn’t exactly been a high priority.

Covering the areas of Ville St. Laurent, Ahunstic-Cartierville and the Town of Mont Royal, my view towards these sewers was somewhat indifferent. I knew that they were often large (up to 15 feet in diameter), but because they consisted of long stretches and were built a relatively short time ago, I had assumed that they would be quite boring and repetitive. Maybe even duller than the industrial parks and suburbs that they pass beneath.

Drainage basins for the island of Montreal as defined by the City’s planning department in 1955. The region in red is the focus of this entry.

These were always the ones I’d get to once I finished exploring more interesting things, but nevertheless I would occasionally find myself looking for ways to access some portion of it. I never had much luck until just recently.

Part of the problem in accessing sewers in Montreal, at least for laymen such as myself, is that 99% of the manholes are situated in the middle of the street. This wouldn’t be an issue if the lids covering them didn’t weigh up to 300 lbs— definitely not the sort of weight you can easily throw around.

Eventually I did manage to find one feasible entry point in a most ideal location— a quiet spot, free from both car and pedestrian traffic. Better yet, this entry point was at the center of the system so trips could be divided up nicely without having to make extensive round-trips.

Despite my low expectations of what these sewers might have to offer, I was quite pleased with my find. Just over a week has passed since the  first visit inside of it, and we’ve only covered a relatively small portion, but so far those expectations have been exceeded.

But before we delve into the system, it’s worth having a peak at what was in this region both before during the time of its construction.

New Frontiers


Island of Montreal circa 1901.

If we go back to the late 1900s, much of this area was uninhabited save for the few hundred people living in the then small communities of Ville St. Laurent and Cote des Neiges. The surrounding land was primarily agricultural. A small network of roads linked the community of Cote Des Neiges at the foot of the Mont Royal to the North shore of the island.

1913 map showing the underground railway connection between the Town of Mont Royal and Montreal.

1913 map showing the underground railway connection between the Town of Mont Royal and Montreal.

A decade later, with the advent of the automobile and tramway came population growth in the area. No longer would the growth of Montreal need to be exclusive to the areas immediately surrounding  the city of Montreal. In 1911, the Canadian Pacific Railway purchased 2,307 hectares of rural land northwest of Cote des Neiges before building a tunnel straight underneath the mountain towards the heart of Montreal.

The acquired land would eventually be turned into the island’s first suburb. Incorporating a European-style radial street plan, this “Model City” would mark the arrival of planned growth for the island. From now on, the city would develop, not solely on necessity, but the anticipation of what the future might entail.

Baby Steps Towards a Sewer System


Detail of 1922 map illustrating the north island’s collector sewer and its two tributaries.

Of course, with this new development came the need for sewers. In 1912 two seven foot concrete collector sewers were constructed. One served the northern edge of Notre Dame de Grace and the second for the Town of Mount Royal. The two sewers merged just northeast of where the Decarie interchange is today, then generally followed the path of what was then known as Farmer’s Road before emptying into Riviere Des Prairies roughly five kilometers away.

I recently discovered a way into the portion running north of  the interchange.

The Notre Dame de Grace Collector constructed sometime around 1911.

At only 7 feet tall, the paris-style sewer “sidewalks” weren’t exactly convenient to walk on, but they did offer a respite from the often mucky conditions found in the centre trench. The half dozen rats scurrying along with me seemed to agree.

1911 plan for the Notre Dame de Grace collector. Source: Province of Quebec Archives, Montreal Region.

Missing in the section I walked through was the 16” pipe which appears on plans for the sewer. Although it’s unlabeled, it’s presumably a water main. This practice of running multiple utilities through the sewer system, while common in cities such as London and Paris never quite caught on in Montreal.


One of several low-tech flow regulators that stand in the way.

But in typical Montreal sewer fashion, nothing is ever as easy to get through as it first appears. A series of flow control gates cut across the sewer every 100 meters or so. In most cases, I could craw I’d you have to climb over the top. Not wanting to have to put up with this, and knowing that Riviere Des Prairies was a good four kilometers further, I didn’t venture too far downstream.

The junction where the two sewers combined. To the right: Notre Dame de Grace. To the left: Cote des Neiges.

At the upstream end, the junction for the NDG and Cote de Neiges sewers can be found, but unfortunately both have been sealed off making further passage impossible.

Growth and the Need for Planning

If the development of Mount Royal marked the beginning of rational planning, it’s clear that its sewage system was still mired in the 19th century way of thinking. At only seven feet tall over a total length of kilometers, there was no way this sewer could ever facilitate the rapid growth that would come decades later. As Ville St. Laurent and the surrounding communities continued to grow steadily, sewage overflows during heavy rainstorms became more common.

Wartime housing in 1944 in the Ville St-Laurent neighbourhood of Bois-Franc for employees of Noorduyn Aviation Ltd. Source: Pistard Archives.

By the time WW2 rolled around, large-scale industrial complexes such as Vickers and Continental Can were beginning to take up large tracts of land. War-time housing units, erected quickly for local employees took up additional real estate. Given the circumstances, new sewer construction wasn’t exactly a high priority. If the system was to be replaced, it would have to wait.

Naturally, things grew even faster in the years following the war. In the late 1940s, the Norgate Shopping Centre (Canada’s first mall) was constructed at Decarie and Cote Vertu. A network of relatively low-density residential areas was begin to spread. With talk of new highways and arteries being built in the near future, it only made sense that the 40+ year old sewer system in the area would require a major overhaul.

Big Thinking, Big Sewers

Open-cut construction of the Meilleur-Atlantique Collector sewer in Cartierville, 1953. Source: City Archives of Montreal.

The new collector sewers were designed far larger than necessary for the time, not to accommodate household and industrial waste, but to handle the storm run-off of the newly paved landscape. As Montreal’s Director of Public Works Department, Lucien L’Allier explained in 1957,  their size was determined based on the region’s “imperviousness” more than actual population. Densely developed residential areas were given the same treatment as those designated for industrial use. “Medium class” residential areas, more likely to contain water absorbing lawns, were put in the same category as railway yards.

1956 diversion ditch for the waters of Ruisseau Raimbault. Its flow is now contained within the Decarie Raimbault sewer. Source: City Archives of Montreal

Determining the size and path of this system was no doubt a tricky task as it involved a fair amount of speculation in how the area would evolve. Given that it was the late 1950s, there was a high level of optimism regarding how much the island would and could be developed. To put this into some perspective, by 1961 there was an expectation that the population for the island of Montreal and outlying areas would reach 7 million by 2000 with much of this growth occurring outside the city of Montreal. While there would be explosive growth over the next two decades, their estimations were a bit off the mark. Today’s population for this same area sits at roughly 3.6 million.

For all the flaws of today’s sprawling metropolis, Montreal’s city planners must be credited for at least attempting to think ahead to the future. As mayor Jean Drapeau stated in 1955, efforts were being made to “not only solve today’s problems, but avoid creating others, and try to anticipate problems 10, 20, even 30 years in advance.”

While Drapeau was clearly referring to the city’s planned autoroutes, the same approach was used when planning the island’s new sewer systems starting to be built around this same time. The crown jewel of these new systems was the Decarie Raimbault.

Enter the Decarie Raimbault System

Sewers constructed for the Decarie Raimbault system between 1956-58. Image source: City Archives of Montreal

The Decarie Raimbault system takes its name from Decarie Blvd and Ruisseau Raimbault, the creek which was diverted underground during the development of the system. At over x miles long, it took three years to complete at a total cost of x number of dollars.


Heading around the bend towards Cremazie blvd.



Possibly the same location taken in 1958 during a final inspection of the sewer.

The first time nel58 and I entered this sewer, we were happy to find that it was easy enough to walk through. With the exception of a few slippery spots, it could be navigated quickly enough by keeping to the edges. This stretch was tunneled through limestone and despite its size could be built using any steel reinforcement. With the exception of one section where a portion of the ceiling has collapsed, it seems to be holding up quite well.


Snow dump hatches inside the Decarie Raimbault collector sewer.

The first noteworthy feature we came across was a rather massive snow dump chamber shown at the beginning of this post. It’s a feature which seems to have been added late— during the 1990s, by the looks of the materials involved. Google Street View now provides us a convenient way of being able to see the facility that contains to the large hatches.


Sewer stretch marks at our midway point.

Carrying on up through the main section of the sewer provided few rewards. It is a 2.5km slog through the same style of pipe, running westward parallel to the metropolitain highway. These sections aren’t particularly deep below the surface, but it was chosen to use tunnel boring machines rather than more commonly used open-cut techniques.

Tunneling of the southern portion of the Decarie Raimbault system in 1958. Image source: City Archives of Montreal

Although not stated explicitly, the disruptions of open-cut construction would have no doubt caused mayhem in an area already well known  for traffic congestion. Before being replaced with the spaghetti junction that exists today, the old Decarie circle was described in 1957 as “chaotic, chronic and intolerable.” Local businesses were up in arms. I don’t imagine that digging open trenches along the neighbouring streets would have helped things any, especially not during a municipal election year.


Junction discovered after travelling roughly 3kms upstream. The passage where I’m standing heads south towards the Decarie expressway.

Eventually a junction appears, with one pipe heading south  and a smaller one continuing further west. We opted for the smaller one with less water coming down through it. Given that it was already late, we didn’t travel much further before deciding to call it a night. Only after I looked the sewer maps upon returning home did I discover we had made it to the middle of the Decarie interchange. Not bad for one night. After all, how many people can say they’ve walked below one of the city’s more infamous traffic arteries? I know, not the most exciting thing in the world, but given the area, you have to take what you can get.

1959 Gazette article announcing the new Decarie interchange. Source: City Archives of Montreal.

Being that this system was only recently discovered, there is still an incredible amount of it left to explore. There are sewers that snake their way up towards the mountain. There’s a connection over to the Meilleur Atlantique collector which most living in Montreal are familiar with because of its tendency to overflow out onto the L’acadie interchange. Basically, there’s enough here to keep me busy for awhile so stay tuned.

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