Urban flooding is increasingly concerning in Canada, where water drainage systems are at risk of being overwhelmed. Natural watersheds have been greatly altered by construction disturbing the natural ways that water flows from rainfall, across the land and into water bodies. The result is that drainage infrastructure must cope with increased water volumes at both higher speeds and flow rates, as well as deteriorated water quality due to pollutants such as oil and organic waste. 

Additionally, stormwater mixes with wastewater in the drainage network in the combined sewer systems that were widely developed in the past. Sudden and heavy rainfall can lead to the network overflowing beyond its capacity, discharging untreated sewage into neighbouring water bodies. This has severe consequences, such as toxic algae blooms that deplete the oxygen found in the water, potentially killing aquatic plants and animals.

In the coming decades, storm intensities are expected to increase, potentially exceeding the design capacity of older networks. Reducing runoff flowrates and volumes through blue-green infrastructure could provide some much-needed relief to drainage systems that may be overwhelmed as stronger rain events become more frequent.

The good news is that there are actions to restore the natural hydrological cycle, which would make Canada's cities more flood-proof.

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