Basement Flooding in Sherbrooke: The Saint-François, the Magog and the Sewers Under the Old Centre

Rivers, sewers and the melt

River flooding announces itself: the City and the province issue warnings, the Saint-François rises at the confluence and along the East ward, and the Magog backs up above the dams. Sewer backup arrives at the floor drain, a basement toilet or the laundry standpipe during or just after heavy rain and smells like sewage; the old centre and the streets on the oldest sewers are most exposed. Groundwater arrives clear at the wall-floor joint and through cracks after long rains and in the melt, and the older houses with stone or block foundations take it through the walls.

Photograph where the water first appeared and when. A river warning, a storm and a smell, or a melt and clear water each point to a different fix.

What the fixes do, and what Quebec requires

A backwater valve is a one-way flap on the drain that closes when the sewer surcharges so sewage cannot flow back into the house; Quebec’s plumbing code has required them on the fixtures below street level of most homes for years, and many older Sherbrooke houses have none or have one seized open. A sump pump with a pit collects groundwater from the French drain around the foundation and pumps it outside; a battery backup keeps it running through the outages that come with the storms. Quebec courts and insurers have held that a missing or unmaintained backwater valve can reduce a claim, which is why an insurer may ask about it.

The City of Sherbrooke has offered programs for backwater valves and protective plumbing at times, and requires a permit for the work; check the City’s current page before signing a quote. Disconnecting the gutters from the sanitary sewer, still common on older houses, is required by the City and takes clean water out of the overloaded system.

• City of Sherbrooke permit and any current program checked
• RBQ-licensed plumbing contractor
• Camera inspection recording and locate
• Backwater valves present and tested on every below-grade fixture
• Sump pump tested, battery backup quoted

Who owns which pipe

The City of Sherbrooke owns the sanitary and storm sewers beyond your property line and the water supply; the lateral on your property is yours, though the City’s by-laws set out who pays for a repair at the property line. A camera inspection with a locate tells you which side a break or blockage is on. Keep the recording; an insurer will want it for a sewer backup claim, and sewer backup and overland water are separate endorsements on a Quebec home policy. The provincial flood-plain maps published after the 2017 and 2019 floods changed what insurers offer near the rivers; ask your broker what is available at your address.

Old foundations and the French drain

Sherbrooke’s older houses have stone, brick and block foundations and clay or no French drains; a waterproofer in Quebec digs the exterior, applies a membrane and a new French drain with a cleanout, and connects it to a sump or the storm sewer where the City allows. Where the lot does not allow excavation, interior drainage to a sump and repointed mortar are the alternative. Extend the gutters well away from the foundation and correct grading before spending on anything underground. Excavation and drainage work must be done by an RBQ-licensed contractor, and the RBQ’s register shows the licence.