Two City of Edmonton drainage branch environmental engineers are engaged in a major challenge that combines large-scale protection of the environment and long-term savings in infrastructure.
Xiangfei Li and Danlin Su are working hard to show Edmontonians how to prevent huge amounts of rainfall and snowmelt from running into the City’s stormwater sewers and (in older areas) the combined sanitary-stormwater system.
They’re eager to work hand-in-hand with City departments planning capital projects so what’s called ‘low impact development’ principles can be incorporated into everything from building roofs to parking lots.
“Cities replace natural ground cover with concrete and pavement,” says Danlin. “And lots of what’s not covered up is usually compacted, all of which significantly reduces the amount of rainfall that’s soaked up before it runs into the drainage system.”
Natural ground cover is part of mother nature’s way of managing stormwater – it absorbs about 50% of rainfall. In a city, less than a third of that makes it into the ground.
Xiangfei says that as the city’s footprint grows, more and bigger pipes will need to be installed to handle stormwater runoff.
“Unless we do something to reduce runoff, the bigger we grow, the more water will go straight into creeks and the river, along with road grit and pollutants like fertilizer and oil,” she says.
“Low impact development’s goal is to build or retro-fit existing development with features that enable more water to be absorbed by the earth,” says Danlin. By reducing stormwater runoff volume right at the source, fewer pollutants end up being piped to the river.
Most of these techniques involve the science of engineering and the art of landscaping architecture, for example laying down various layers of rock and gravel before sodding or planting a garden over a gently sloping, permeable pipe. All of the techniques result in more water absorption and they often come with the added benefits of enhanced aesthetics and improved natural habitats.
Xiangfei and Danlin have been meeting with city architects, developers and builders to promote low impact development. The engineers also want City departments to work with them to incorporate low impact development principles in their capital projects (providing real-life demonstrations, backed up by hard numbers, that prove the effectiveness of the techniques).
“There may be future saving in infrastructure costs if we can reduce the size of the pipe we must use, and the treatment facilities we must have,” says Danlin. “And the softer environmental impact makes us more respectful of the Earth.
“It’s in everyone’s interests to build this way.”
The drainage branch has produced a comprehensive design guide to low impact development.