How does Groundwater apply in flood hazard?

Groundwater is not considered in the Provincial Flood Hazard Map, since their flood studies focus on overland river flood hazards (the situation when high water escapes the river and inundates the floodplain). Groundwater has different dynamics than overland river flooding and can occur under two conditions:

  • Concurrent with river flooding: the groundwater table rises alongside overland river flooding
  • Without river flooding: In areas with a barrier or upstream reservoir to mitigate overland river flooding, the groundwater table can still rise

Reducing our risk to flooding, both overland river and groundwater flooding, to acceptable levels requires a combination of strategies, including upstream, community and property-level measures.

How do we protect against the impacts of groundwater?

Barriers and reservoirs don’t fully protect against against groundwater rising and entering basements during river floods.

The City is currently working to identify the locations with the highest risk of groundwater flooding during river floods, and assessing the effectiveness of different mitigation approaches.

Where groundwater is a risk, basement flooding can typically be mitigated by:

  • Requiring sump pumps and backflow valves. Recommending no new living spaces (like kitchens, living rooms, and bedrooms) below the 1:100 flood level with entrances, storage and laundry allowed
  • At the next phase of engagement, The City will present information on groundwater risk areas and mitigations to inform discussions about possible regulations.

What do we want input on?

We want to hear any concerns or questions you have about groundwater flooding during river floods.