The Rainway vs. the Atmospheric River

When they heard that an atmospheric river was in the forecast, Vancouver city staff knew their new rainway was about to be put to the test.

The green stormwater system, the first of its kind to be designed by the city, was to be hit with a volume of water that would break the record for the wettest Oct. 19 in recorded history.

It might be an engineered creek, but there used to be a real one where St. George Street is now. After colonization and the urbanization of the city, it was buried along with almost every one of the city’s waterways, of which there were more than 50.

But just because they’re underground doesn’t mean they’re not there. Walk past a manhole on St. George Street on a rainy day and you can hear the unmistakable sound of running water.

“Water always comes back to the same pathways,” said Julie McManus, project manager with the city’s green infrastructure branch.

The idea to bring the St. George creek back in some way had been around for two decades. Local advocates petitioned the city for years. Analysis found that daylighting the creek wasn’t possible due to sewer and gas lines in the way.

But there was something that the city could create: a rainway.

It’s a landscaped path with trees and plants for rainwater to be stored and filtered of pollutants, while reminding residents of what was once the creek’s historic route as it flows downhill.

The stretch of the rainway on St. George Street between Fifth and Seventh avenues is largely complete. It will be extended uphill to Eighth Avenue in the coming months.

So when the atmospheric river came to the coast, McManus went to check it out on Oct. 19. There were many people stopping by, from members of her team and other city staff who had heard about the project to local residents who had been waiting for years to see the rainway in action.

The storm hits

The rain came down the rainway just as it should.

The water wound its way through the little dams and weirs of the landscaping, cascading down St. George Street, “mimicking nature like a real stream,” said McManus.

“It’s one thing to see how the design is going to work on paper, and another in real life.”

While there was no doubt that the rainway would work, there was worry that the atmospheric river might harm its young plants, which had been put in only three weeks earlier. Among them were Juncus effusus, a hardy member of the rush family, and native pollinator plants like beardtongue, western columbine, wood sorrel and tiger lily.

Thankfully, they survived.

The team also kept their eye on overflows.

The rainway was designed to handle 48 millimetres of water in a 24-hour period, an average rainfall event. But the atmospheric river brought about 67 millimetres to Vancouver that day, and even more in surrounding areas, such as 135 millimetres in West Vancouver.

If the city’s other green infrastructure projects, from bioswales to rain gardens, are any indicator of success, the rainway should have been able to handle a challenge. Those projects have drawn down water from the surface faster than they were designed to.

They’ve also done well removing pollutants. During tests, they’ve removed chemicals like 6PPD-quinone, a stabilizing additive often found in rubber vehicle tires that’s harmful to salmon, and suspended solids, like plastics and metals, at 98 and 99 per cent respectively.

So how did the rainway do during the atmospheric river?

Even with the arrival of more rainfall than it was designed to hold, the rainway was able to contain it. City staff on their inspections did not observe any water entering overflow pipes.

A living classroom

The storm that October weekend proved to be a deadly one.

The event killed four people, two on Vancouver Island and two in Coquitlam, where a woman’s house was swept away in a mudslide. The North Shore and the Tri-Cities still have many waterways on the surface, some of which burst their banks during the atmospheric river.

When such storms hit Vancouver, which is more paved and urbanized, the extra water manifests as flooding on the street due to backed up sewers.

“They become so inundated because there’s nowhere for the water to go,” said McManus. “So we can help alleviate some of that flooding by getting areas for water to go safely without going into our sewer system.”

Students at Mount Pleasant Elementary School, which backs onto the rainway, have already been learning about it. They will be participating in an outdoor rainway-inspired art exhibition at the end of the school year.

“I really hope to see it used as a living classroom,” said McManus.

The rainway has already had many lessons to teach the green infrastructure branch at the city. Now that the lesson on atmospheric rivers is over, they’ll be waiting to see how it fares in the event of a drought.

“We’re trying to include plants that can be resilient throughout heavy inundation of rain through winter, but also able to tolerate drought through summer months, often plants similar to an ephemeral wetland.”

The heat dome of 2021 taught cities the importance of tree canopy to cool urban streets. The area surrounding the rainway has a deficit of trees. The city has planned 35 new trees for the area. So far, half have been planted. Together with the greenery of the rainway, it is set to be a cool refuge for a hotter-than-average neighbourhood during extreme heat events.

Trying to engineer nature is tricky work, McManus says: “Nobody can 100 per cent predict what nature is going to do.”

The water quality and quantity are proven successes. But her team at the city is curious about biodiversity too, down to the insects, microbes and soil health. They’ll be keeping an eye on those in the new year.

On the horizon for the area is a very different type of growth: densification. It is spurred by the upcoming Broadway subway, which will have two stations nearby.

Projects like the rainway are proof that urbanization doesn’t have to be limited to the grey of concrete.

“I think it makes it even more important as we densify and people live in multi-family, multi-unit dwellings,” said McManus, “to be able to have some access to green space where they can get natural respite.”