--- title: the spring that reached montreal canonical_url: https://ensurance.app/guide/the-spring-that-reached-montreal markdown_url: https://ensurance.app/guide/the-spring-that-reached-montreal.md subtitle: 2017 flooded more than 430 homes. the overflow is the other way water leaves the island. category: ecosystem-services --- # the spring that reached montreal *2017 flooded more than 430 homes. the overflow is the other way water leaves the island.* In the spring of 2017 the river came into homes on the island of Montreal. The city's report to the standing committee calls it the worst flooding since **1976**. **Over 430** homes flooded. **Some 1,100** residents were displaced. That is the failure that reached people. The rest of this page is what kind of water it was, and what kind it was not. The island depends on spring stage staying off those floors, and on the combined sewers not using the river as a relief valve. The people in the boroughs, and the river that receives the overflow, depend on the island treating both of those as its own problem. :::johnson **the spring reached the kitchens. the sewer reaches the river.** Two different waters. One island. Neither figure in this page is a price. ::: ## where the 2017 water was The flood struck boroughs and linked cities along **Lac des Deux Montagnes**, **Rivière des Prairies**, **Lac Saint-Louis**, and the **St. Lawrence**. The report names L'Île-Bizard–Sainte-Geneviève, Pierrefonds-Roxboro, Ahuntsic-Cartierville, Rivière-des-Prairies–Pointe-aux-Trembles, Sainte-Anne-de-Bellevue, and Senneville. If you live in one of those names, you do not need a regional average to know which street went under. The same report says Hydro-Québec, Bell, and Gaz Métro (now Énergir) worked to protect their own infrastructure, and that the vulnerability of those networks was incompletely understood. The river reached the grid's edge. The notes do not say what that cost the utility. The ice storm that took trees onto lines is a different season and a different series. Insurance Bureau of Canada, using CatIQ, said on 1 September 2017 that spring flooding in **Ontario and Quebec** caused **more than $223 million** in insured damage. **Over $106 million** of that was from 5–7 April. **Nearly $117 million** was from 5–7 May. That total is two provinces. It is not a Montreal-only loss, and it is not a premium for this island. Anyone who divides it by the 430 homes is inventing a number the bureau did not publish. The city's report calls 2017 the worst civil-protection disaster on the island since the 1998 ice storm. This page does not restate 1998. Those totals were not re-opened. ## what 2019 was, and what it was not In spring 2019 the island declared a state of emergency. Damage on the island was smaller than in 2017. A Montreal Gazette count, as of Friday during the emergency, put the island at **251** people evacuated, **192** homes flooded, and **49** homes isolated. Earlier in the same week, other news counts of the island were lower. These are snapshots taken while the water was still the story. They are not a closed loss assessment. The same week, the provincial picture was much larger. Thousands of people had left homes across Québec. Sainte-Marthe-sur-le-Lac, off the island, lost a dike and accounted for a large share of those evacuations. That town is not part of the island total. Folding it in would make Montreal look like a disaster it did not, by itself, record. No death toll for either spring is in these notes. This page does not add one. ## the other water, the one in the pipe Spring high water is the river entering the island. Combined-sewer overflow is the island entering the river. When rain is hard, or when snow melts, the interceptors fill and wastewater discharges to the waterways. The city's English page on the ozone works says those overflows are expected, including during periods when treatment capacity was reduced for construction. The retention network exists so that some of that volume waits instead of discharging. Nearly **49 million litres** of capture, a Rockfield basin of up to **45,000 cubic metres**, and a Lavigne basin described as **20,000 square metres** are the hardware. They are not added together on this page. They are not the flood of 2017. A basement in Senneville and a discharge at the plant are different mechanisms that share a season. The plant those tanks feed is Jean-R.-Marcotte, on the St. Lawrence. The 16 March 2022 deck revised the disinfection budget to **$696.2 million**, with a design flow of **40 cubic metres per second** and commissioning aimed at mid-2025. The city page of **27 March 2026** carries phases 4 through 6 out to **December 2028**. The schedule slipped against the deck. Both dates stay, because picking one to make the story neat would be a fiction. The budget is a treatment project. It is not an annual premium, and it is not the insured loss. GCoM's Montréal profile marks extreme precipitation as **high**, on a medium-term timescale, and marks **river flood as "Not known."** The city's 2017 report is a direct contradiction of that second field. The profile was not corrected in these notes. A covenant page that cannot see a flood the city has already counted is a data problem. It is not evidence that the kitchens stayed dry. A city reader who wants the general frame for public flood works can use [governments](/solutions/governments?from=guide&topic=montreal-island). The page describes regional flood mitigation as a kind of work. It does not quote a Montreal unit, and this series does not have one to hand you. The city's own account of the tanks is the closer door: [retention structures](https://montreal.ca/en/articles/retention-structures-limiting-wastewater-discharge-14459). If you were in one of the 2017 boroughs, or you operate a pipe that still surcharges to this river, and you want a person rather than a pamphlet, write through [contact](/contact?from=guide&topic=montreal-island). Say which shore. The topic is how the desk knows it was this island. ## two maps that disagree A person standing in Pierrefonds-Roxboro in May 2017 did not need a covenant profile to know the river had crossed the sill. The GCoM mark of "Not known" is a second map, kept for a global network, that does not match the city's report. Extreme precipitation is marked high, on a medium-term horizon. The island has already had the short event. Holding both maps without averaging them is the useful habit. One is a flood that reached named streets. The other is a form that has not caught up. The city is also on the C40 Urban Flooding Network. A June 2025 workshop note names Montreal among cities sharing practice. Membership is how peers talk. It is not a count of homes, and it is not a fund. The homes remain the 2017 report's number. The practice-sharing remains a network list. The overflow and the spring can arrive in the same month and still be different physics. Snowmelt raises the river and fills the pipe. A basement can take river water at the foundation and take sewage at the floor drain. The city's hardware answers the second path, up to the volume of the tanks. The first path is the shore. The borough list is mostly the shore. The plant is the pipe. Say which one you mean before you ask who should pay. ## what to hold onto The living thing that reached people is the spring stage of this fluvial reach. The living thing the overflow reaches is the same river, used as spare capacity. **Ensurance** would fund that reach. It is not a retelling of the emergency, and it is not the ozone contract. The person who already published the count is the City of Montréal, in the 2017 report. The specific next step is to read that report against the GCoM field that still says the river flood is unknown, and to keep Sainte-Marthe-sur-le-Lac on its own shore. The last page in this series says who already works the tanks, and why that work is not a watershed fund. Urban flooding, as a general method, is [nature-based solutions for urban flooding](/guide/urban-flooding-nature-based-solutions?from=guide). Use it if you want the method. Stay here if you want the island. ## frequently asked questions ### how many homes flooded in montreal in 2017? The city's report says over 430 homes flooded and some 1,100 residents were displaced. It calls that spring the worst island flood since 1976. The insured figure above $223 million is Ontario and Quebec together, not an island total. ### what happened in the 2019 montreal flood? The island declared a state of emergency. A Gazette count during the emergency, as of Friday, was 251 people evacuated, 192 homes flooded, and 49 homes isolated, on the island. It was smaller than 2017. Sainte-Marthe-sur-le-Lac's dike failure is off-island and is not that count. ### what is a combined sewer overflow here? When rain or snowmelt exceeds the interceptors, wastewater can discharge to the river. The city builds retention structures to hold some of that volume for Jean-R.-Marcotte. Overflows are still expected in hard rain and during the ozone works. That is a different event from a basement flooded by the spring river. ### does the global covenant of mayors count this flood? The Montréal profile marks river flood as "Not known," and marks extreme precipitation as high. The city's 2017 report is the counter-record. The profile was not fixed here. ## sources [City of Montréal, 2017 flood report](https://ville.montreal.qc.ca/pls/portal/docs/PAGE/COMMISSIONS_PERM_V2_FR/MEDIA/DOCUMENTS/DOCCONSULT_ANG_20171212.PDF) — homes, displacements, boroughs, utilities. [Insurance Bureau of Canada, 1 September 2017](https://www.newswire.ca/news-releases/spring-flooding-in-ontario-and-quebec-caused-more-than-223-million-in-insured-damage-642449303.html) — insured damage for Ontario and Quebec, not Montreal alone. [Montreal Gazette, 2019 floods](https://montrealgazette.com/news/quebec-floods-red-cross-to-give-600-to-hardest-hit-families/) — island counts during the emergency. [CBC, Montreal state of emergency](https://www.cbc.ca/news/canada/montreal/montreal-state-of-emergency-flooding-pierrefonds-1.5113169) — the declaration. Island counts that week were still moving. [GCoM, Montréal](https://www.globalcovenantofmayors.org/cities/canada/canada/montreal/) — river flood marked not known. [City of Montréal, retention structures](https://montreal.ca/en/articles/retention-structures-limiting-wastewater-discharge-14459) — overflow hardware. [Ozone works, English project page](https://montreal.ca/en/articles/ozone-disinfection-construction-jean-r-marcotte-water-treatment-station-27451) — overflows in hard rain and snowmelt. ## the series - [montreal stands in the river](/guide/what-montreal-stands-in?from=guide) - [who depends on the river at montreal](/guide/who-depends-on-the-river-at-montreal?from=guide) - [the lachine rapids are not a pipe](/guide/the-lachine-rapids-are-not-a-pipe?from=guide) - [the spring that reached montreal](/guide/the-spring-that-reached-montreal?from=guide) - [who already works the montreal overflow](/guide/who-already-works-the-montreal-overflow?from=guide)