With more rain forecast for Vancouver this weekend after last month’s atmospheric river, the new St. George Rainway showcases how gardens can help cities manage flooding, reduce polluted runoff, and promote biodiversity.

The new pebbled garden in Vancouver’s Mount Pleasant neighbourhood will span four blocks when completed in spring 2025, but it is already proving its effectiveness after October’s deluge. The pouring rain filled the gully, becoming a river, as weirs—small barriers placed every few metres—slowed the stream, allowing water to absorb into the soil and roots instead of flooding streets and gutters.

The rainway passed its first test: a record-breaking week of 100+ millimetres of rain, Julie McManus, project manager at the City of Vancouver Green Infrastructure Implementation Branch, told The Energy Mix in an email.

“During the atmospheric river, several City staff visited the rainway and observed that it was performing very well,” wrote McManus. They observed all the dams working, giving the water time to absorb, and no overflow. They expect the rainway to function even better when it’s fully built and the young plants are rooted deeper, McManus added.

The garden comes as climate change challenges sewer systems by making extreme rainfall more frequent. In Vancouver, the system combines stormwater and sewage in the same pipes, though the city is in the process of separating them. After October’s atmospheric river, 14 recorded leaks in the system sent untreated sewage into local bodies of water, reported The Vancouver Sun.

Rain gardens are one way to take pressure off the sewers. These plant-based design choices, called “softscaping,” also create resilient native ecosystems that contribute to biodiversity, urban cooling, and local enjoyment.

It’s too soon to monitor how well the rainway filters pollutants, but Vancouver’s other rain gardens have worked well. Tests found [pdf] that rain gardens successfully filtered out stormwater pollutants, including plastics and 6PPD-quinone—a tire chemical harmful to salmon—by up to 98%.

“We will be planting 35 new trees to the rainway, which, along with other native shrubs in the rainway, will support evapotranspiration of rainwater,” wrote McManus. “Not only does this help manage rainfall, it also provides urban cooling in a neighbourhood that is below the City’s canopy targets.”

Rediscovering Lost Streams

The rain garden was first envisioned by volunteers in 2008 [pdf] to revitalize the headwaters of te Statlew, one of many “lost streams” Vancouver buried as it urbanized, reported CBC News. Residents frustrated with rainfall flooding their basements connected with storytellers who wanted to bring the ancient buried stream back into public space. Then the City took notice: blue-green design projects to manage stormwater fit with its planning goals. In 2016, the St. George Rainway officially partnered with Vancouver as a stakeholder in the Integrated Rainwater Management Plan.

While te Statlew was not restored to the surface, the rain garden’s project brief states an aim to “honour the lost stream while also enhancing the local environment.”

Stormwater Planning Meets Community Leadership

The City carried out three-years of engagement from 2021 to 2023, including residents in rainway decisions through festivals, surveys, and school events. The garden’s final proposal removes a lane of traffic to create a car-free area and a bike path, and was officially accepted by the City of Vancouver in 2020. It is projected to cost C$6.2 million, 60% funded by the federal government.

Green infrastructure like the rainway plays a part in Vancouver’s 2019 Rain City Strategy target to capture and treat 90% of its stormwater. McManus said the rainway can treat 17,000 cubic metres of water per year, the equivalent of 6.8 Olympic swimming pools and 90% of the average stormwater flowing through the street. It’s an important start, but the city still has work to do to adapt to more extreme rain events, McManus said.

“A historic extreme storm event like the one we experienced in October requires large amounts of storage to protect downstream property and infrastructure,” she wrote. “Every component of green rainwater infrastructure that we can add to neighbourhoods helps.”