Rainwater and flood zones in Dollard-des-Ormeaux
Updated September 28, 2026
In Dollard-des-Ormeaux (DDO), in the West Island, streets drain through catch basins into a storm sewer kept apart from the sanitary sewer, and part of that water goes through Centennial Lake, a retention pond. The City of Montréal lists DDO among the areas concerned by heavy rain, but not by high water.
According to the mayor, the network is designed for about 80 mm of rain in major storms, and neighbourhoods from the 1950s to the 1970s are hard to retrofit. The city has built an underground retention basin at Terry-Fox Park and started a second one in another sector, where residents describe water collecting in the street in heavy rain.
Heavy rain events
What public sources report about heavy rain in Dollard-des-Ormeaux, at sector level.
According to the city, 100 to 170 mm of rain fell in about one hour in some areas, under a nearly stationary storm cell, so some neighbourhoods were hit much harder than others. The volume of rain exceeded what Centennial Lake, a retention pond, is normally meant to handle. Radio-Canada reported that the Montréal fire department named DDO among the hardest-hit areas. The city does not say how water entered homes; residents quoted by La Presse describe runoff coming from a neighbouring cemetery.
Sources: Ville de Dollard-des-Ormeaux, Pluies diluviennes du 20 juin 2026 : foire aux questions · Radio-Canada, 21 juin 2026 · La Presse, 21 juin 2026
Residents of one sector of DDO told The Suburban that since 2024, in heavy rain, water collects there and reaches nearby homes, as it did that day. At Montréal-Trudeau airport, outside the city, MétéoMédia (The Weather Network) reported 57.5 mm in under an hour and 81 mm for the day. The article does not say whether sewer backups also occurred.
Sources: The Suburban, July 23, 2025 · MétéoMédia, 23 juillet 2025
During the remnants of Debby, which dropped more than 150 mm in 24 hours on Greater Montréal according to the Communauté métropolitaine de Montréal, CBC News reported basements flooded by sewer backups. According to the city, the cases its public works department checked came from the storm sewer, not the sanitary sewer: a storm-sewer backup.
Sources: CBC News, August 10, 2024 · Communauté métropolitaine de Montréal, communiqué de décembre 2025
Good to know in Dollard-des-Ormeaux
- Montréal's flooding page lists Dollard-des-Ormeaux among the areas concerned by heavy rain, not by high water. It explains “zones cuvettes”, low spots where water collects more easily, and links to the agglomeration's vulnerability map. (Ville de Montréal, Inondations)
- The city's sewer system is separate: sanitary on one side, storm on the other. Street runoff enters catch basins along the curbs; part of it is held for a time in Centennial Lake, a retention pond, then released into the Rivière des Prairies. (City of Dollard-des-Ormeaux, Sewage system)
- Building by-law R-2025-203: every connection to the sanitary or storm sewer must have a backwater valve, which the owner keeps in working order. The city is not liable for backup damage if these devices are missing or poorly maintained. (Ville de Dollard-des-Ormeaux, règlement de construction R-2025-203)
- Reverse-slope driveway: the catch basin at the bottom must connect to the storm sewer, never to the garage pit, which is on the sanitary sewer. The city's brochure adds that the driveway must rise at least 6.5 cm above the curb, measured at its centre. (Ville de Dollard-des-Ormeaux, dépliant sur la prévention des infiltrations d'eau (2025))
- After the August 2024 rain, the city built an underground retention basin at Terry-Fox Park, fully working by the fall of 2025. Construction of a second underground basin, in another sector of the city, began in June 2026. (Ville de Dollard-des-Ormeaux, Pluies diluviennes du 20 juin 2026 : foire aux questions)
- According to the mayor (The Suburban, July 2026), an engineering review found the network built to North American standards, designed for about 80 mm of rain in major storms. Neighbourhoods from the 1950s to the 1970s are hard to retrofit; new developments must include underground retention. (The Suburban, July 4, 2026)
Rivers and lakes: what the check does not cover
The check is about the rain that falls on the area and runs off over the ground. River and lake flooding is not part of it: in the simulation, a nearby river or lake holds no water. For a waterfront property, the official map comes first.
What we know about the ground in Dollard-des-Ormeaux
These values come from the public sources the check uses. They describe the area, not an address.
| 1 m terrain model (NRCan HRDEM) | Available across the whole area |
|---|---|
| Nearest rainfall gauge (ECCC) | Sainte-Dorothée (Laval), 4.2 km awayLocal rainfall statistics. |
| Municipal street drains | Modelled, from the open municipal catch-basin inventory |
| Mapped culverted road crossings | 0Culvert lines mapped in OpenStreetMap (ODbL). |
Data Source: Environment and Climate Change Canada, Short Duration Rainfall Intensity-Duration-Frequency Data, used under the ECCC Data Servers End-use Licence.
Area analysed: adapted from Statistics Canada, Census Subdivision Boundary File (cartographic), 2021 Census. This does not constitute an endorsement by Statistics Canada of this product.
Probed on September 28, 2026.
The official map and what it does not show
Québec's flood-zone maps cover rivers and lakes. They do not show rain water collecting on a lot, in a low spot or at the bottom of a sloping driveway. Check the official map for the address first: it is what says whether a property is in a flood zone.
FloodVerity does not reproduce these maps and does not state any regulatory zone.
Check an address in Dollard-des-Ormeaux for $39
We drop a 100-year, one-hour design storm on the ground around the property, route the runoff, and email you the peak depth of rain water at the address, where it collects, a map and a 3D view.
What the check does not do
- This check models rain falling on the area itself and running off over the terrain. Water arriving from a river or lake, sewer backup, ice jams and storm surge are not modelled.
- The pipe network itself, roof and lot drainage, and sewer backup are not modelled.
- Where the structures inventory records a culverted road crossing, it is lowered to a partly blocked opening rather than solved hydraulically.
- It does not replay the storms described on this page: it applies a 100-year, one-hour design storm.
- It is a screening: a simulated storm on public terrain data, not a hydraulic study, not an official flood-zone determination, not an insurance opinion.
Notaries and brokers in Dollard-des-Ormeaux
We run the same check over a list of addresses and deliver a spreadsheet ranking them by the modelled rain depth. Priced per address, on quote.
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The FloodVerity check is a screening: it applies a design rainstorm to public terrain data and simulates where the rain runs and collects. It is not a hydraulic study or an official flood-zone determination, and it covers neither river and lake flooding nor sewer backup.