Managing Stormwater
A Two-Tier System
The SEFC Official Development Plan provided specific direction on some aspects of water management for the site. Among them was the idea that stormwater would be showcased in a wetland, rather than hidden in conventional underground storm sewers away from public awareness. This created challenges for Stantec, which designed the stormwater collection and treatment system. “Ideally, for an area of this size, we would have had a larger stormwater pond,” says Garry Romanetz of Stantec.
“However, there was only so much land available for Hinge Park and the wetland. So we were forced to work backwards and figure out how much water we could convey and treat within the site constraints. This resulted in a two-tier stormwater system, so we were able to best utilize the lands that were made available.”
The two-tier system collects “cleaner” stormwater separately from “dirtier” water. When rain falls on building roofs and podium areas, it is stored in cisterns for reuse. When the cisterns are full, the rainwater is discharged directly into False Creek. “Dirtier” rainwater is that which falls on streets – where vehicle traffic and human activities are heavy. Depending on the location and the site grade, this water is handled in different ways. Some is collected and channelled to the wetland in Hinge Park, where it is calmed, circulated and cleaned by plants (see pages 17-18). Elsewhere, the water enters infiltration galleries underground, which use layers of gravel and sand to remove contaminants before the water enters False Creek. A bioswale along Ontario Street will also pre-treat water prior to discharge from the east end of the site.
The stormwater management plan was also influenced by a flood protection elevation that had to be established at the foreshore. This established roadway grades along First Avenue, and minimum building elevations. In some areas, this required nearly a metre of additional fill.
“Cleaner” stormwater is first used by building landscape systems and stored in cisterns – or, if full, discharged to False Creek. Credit: Durante Kreuk, 2009
A Showcase for the Future
Re-thinking centuries of stormwater management proved challenging at times for the integrated design team at SEFC. “I’ve worked on a number of different Olympic venues,” says Garry Romanetz, “and this was the biggest challenge in terms of trying to achieve all the objectives within the constraints presented. It challenged us to provide multiple solutions, because the objectives for the environmental and planning group at times are different from the engineering or the operations and maintenance divisions. It was challenging to see a job scrutinized to the extent this one was.”
“Inverted crown” streets (with collection channel at centre rather than sides) help make stormwater visible to residents. Inset, centre and right: Infiltration galleries of sand and gravel help trap contaminants in “dirtier” stormwater. Credit: Gary Romanetz, 2009
Wally Konowalchuk, engineer with the City of Vancouver, agrees. “For example, part of the idea of showcasing water was to try to get it on the surface to highlight that we are trying to use it. But water on the surface presents challenges, such as accessibility, and whether people in wheelchairs will be able to get through without facing streams of water, and if it freezes in the winter, will it be a huge icy area.” Similarly, a desire for the permeability and aesthetic appeal of paving stones had to be balanced with concerns about long-term maintenance. Says Konowalchuk, “It’s hard to bring everyone to a consensus on how to change things from how they are traditionally done.”
Romanetz says the end result, including some inverted crown streets, a wetland, infiltration galleries, a bioswale and a two-tier stormwater system, is a plus for the City. “They’ve got a system that is unique,” he says, “and that will offer them tremendous opportunities to evaluate and showcase similar green stormwater alternatives in the future.”
“It’s hard to bring everyone to a consensus to change things from how they are traditionally done.”
Wally Konowalchuk, City of Vancouver
The Hinge Park Wetland
At first glance, it’s a pleasant place to sit and let the kids play. But this wetland isn’t just a community amenity. It also cleans the water that runs off the Village’s grounds and streets.
“We developed a layout for the wetland in Hinge Park that’s linear and meanders, to reduce the water velocity,” says Garry Romanetz of Stantec. “Basically, the longer you are able to put the water through the wetland, the more it gets cleaned before it is discharged to False Creek.” Hinge Park was designed by an integrated design team led by PWL Partnership Landscape Architects and including representatives from a variety of disciplines, including Stantec.
Two levels of aquatic plantings will help trap sediments and contaminants in the Hinge Park stormwater treatment wetland. Credit: PWL Partnership Landscape Architects., 2009.
Silt and debris settle in the channel and get trapped by two levels of wetland plants. “They’ll keep the water fairly clean,” says John Clelland, the City’s Coordinator for Hinge Park. “It will never be crystal clear because you’re looking at natural water – there will be algae and water bugs and fish swimming around.” (Already, there are “tens of thousands” of native stickleback minnows.) The channel opens into a pond where contaminated sediments will collect. These can be pumped out periodically and taken to landfill, instead of entering the ocean.
The wetland also collects water from streams that were long ago paved over but still flow underground. This groundwater base flow will assist in keeping the system wet even during dry periods – with an irrigation system as a final backup if needed. A pumping system also ensures good circulation.
“We often dealt with competing issues when designing various components of the system,” says Wally Konowalchuk, the City engineer overseeing the project. “The pump is not needed for the functioning of the wetland itself, and on the face of it, it doesn’t sound very sustainable. But there are public health concerns about stagnant water and breeding mosquitoes, so we installed it.”
The entire system helps people see and understand the flows of water in their city. “The general public has no idea what’s under the road,” says Clelland. “Everyone knows there are pipes, but they don’t think about what they are or where they’re going. Here, we have taken rainwater that we usually hide and created a park. It helps prolong the life of the sewage treatment plant, plus we have birds, we’ll have animals. It will be a wonderful place to be, and also a great learning experience for people.
Credit: (Left photo)Danny Singer, 2009. (Right photo) Aqua-Tex Scientific Consulting Ltd.
“We have taken rainwater that we usually hide and created a park. It will be a wonderful place to be, and a great learning experience for people.”
John Clelland, City of Vancouver
“In Olympic Village and in the park, we’re thinking about today and about future generations, by being sensible and practicing good stewardship.”