Summer in Canada has a recipe: sunshine, water, sand and stone. And in Edmonton, an innovative public project is letting locals experience that mix while swimming at a public pool.
Designed by architecture and landscape architecture firm GH3, the Borden Park natural swimming pool is the first of its kind in Canada: A pool in which the water is filtered without chemicals, primarily by passing over plants and rock.
Now in its first full season, it’s innovative and also beautiful – combining technical advances with architecture of great clarity and rigour.
“When you think about clean water, the most perfect vision of that is the Canadian Shield: The clarity of the water against the stone,” says Pat Hanson, the architect who leads GH3 with partner Raymond Chow. “So we built on that, and all the qualities that those materials evoke.”
The firm designed a long bar-like building to contain change rooms and some mechanical equipment. Its main material is rock: hunks of it, all a uniform grey, contained by a wire cage. This system, known as a gabion wall, is most often used in retaining walls and other works of infrastructure. Here it hints at a visceral connection with nature.
The city has been making improvements on Borden Park, which dates to 1906, for about a decade, says Edmonton city architect Carol Bélanger. In the present, he says, the public “came out strongly” for the idea of creating a naturally filtered swimming pool.
The rebuilding job went to the Toronto practice GH3. They engaged engineering firm Polyplan to design the natural filtration process, similar to ones widely in use in Germany and France. “The challenge was bringing that to Canada,” Hanson says, “working through a more stringent set of regulations about water quality.” The basic idea is “not dissimilar to how we treat drinking water with a charcoal filter.”
In the two pools, bathers – in controlled numbers, after a good shower – immerse themselves in water that contains a small quantity of algae. It is cool, greenish and free of irritating chemicals. And thanks to the plant life, it has a distinct texture, more like lake water than a swimming pool. “It’s softer, silkier and it feels denser to me,” Hanson says.
The outflow from the pools passes through a loop. It is first sprayed onto a set of plants; these absorb micro-organisms that are harmful to people, which the plants absorb as nutrients. Then the water slowly filters through 2.5 metres of granite gravel, dropping off dirt and contaminants. From there, it is either heated and UV purified, or else passes through a “hydrobotanic” pond; here, zooplankton attack harmful micro-organisms in the water, part of an ecosystem that supports lilies and reeds.
GH3’s architectural response to all of this shows off their minimalist sensibility very well. They are among many distinguished design firms who’ve done public work in Edmonton under Bélanger’s guidance. They’d already completed a nearby pavilion in Borden Park, which won a Governor-General’s Medal in Architecture.
The pool’s architecture starts with those gabion walls. “The idea that the water was filtered through granules led to the idea that a building could be made of stone and be breathable,” Hanson says.
Next to it, the change-room building features tall doors of dark-hued, mild steel. These open onto an interior lined with only one material: fine marine-grade plywood with a blackened finish. The details of the finishes are subtle. With few fixtures, the space has all the spare clarity of a high-end spa interior. It is the most elegant of boxes, a dark container from which to emerge, chlorine-free and refreshed.
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