A university professor and an industry association representative made the environmental and business case for the greater use of permeable pavement at recent Construct Canada seminar.
The seminar entitled Construction and Performance of Permeable Pavement in Cold Climates, featured University of Toronto Professor Jennifer Drake and Robert Bowers, director of engineering for the Interlocking Concrete Pavement Institute.
There have been three, one-in-100 and five one-in-50-year storms in the Greater Toronto Area during the past eight years, said Drake, citing Credit Valley Conservation Authority statistics.
The washout of the Finch Avenue Bridge in Toronto a few years ago and last year’s flooding of the city’s Don Valley Parkway are telling examples of the impact of urbanization and the inadequacies of traditional stormwater management systems to control stormwater runoff, said Drake, who is an assistant professor with the university’s department of civil engineering.
"Our drainage infrastructure is undersized to provide the desired level of safety for our communities," she said, pointing out that Canada’s "infrastructure deficit is estimated at $123 billion, of which $31 billion is for water/wastewater."
Some of the long term negative impacts of untreated stormwater runoff include the degradation of water quality, closures of water recreation areas, and a loss of habitat and biodiversity from the pollutants washed into nearby watercourses.
Then there are the safety and public damage risks.
"Insurance doesn’t cover overland flooding which means they (homeowners) can’t get coverage," said Drake, noting that while disaster relief funds can be made available, ultimately that relief "is paid for by the taxpayer."
The comments were a lead into an overview of the function and benefits of permeable interlocking concrete pavement (PICP) which can remove more than 80 per cent of suspended solids, said Drake, an advisor to the Toronto Region Conservation Authority control study of a parking lot at the Kortright Centre in Kleinburg, Ont.
PICP cleans, detains and reduces the amount of stormwater which has to be handled by infrastructure systems, said Bowers.
In projects where it’s in place, the stormwater drainage infrastructure can be much smaller and less land is required to accommodate that infrastructure, he added.
PICP is a multi-component system consisting of a below the ground sub-base, base, and bedding layers and permeable joint materials comprised of different sized open graded aggregate. The only visible elements to the public are the concrete pavers and a concrete curb which is necessary to hold the pavers in place.
Stormwater flows through the fine aggregate filled joints between the pavers and slowly passes through the different layers, he explained.
"There are different ways we can design these systems," said Bowers.
These include full infiltration, partial infiltration which requires an outfall sloped to the storm drain and which would be needed for finer soils; and no infiltration This option is used in locations where infiltration is not desirable — such as a salt yard — or for rain harvesting, he said.
One of the largest applications of PICP was the construction of a six-acre parking lot at the U.S. Cellular Field baseball park, the home of the Chicago White Sox.
As part of that city’s Green Alley project, it’s also installed to eliminate flooding and beautify back lanes, said Bowers.
But care has to be taken in the construction of PICP. For example, the subgrade has to be as "flat as possible" without minimal or no compacting. Compaction will reduce the permeability of the native soils.
Another requirement is not to make the width of the joints between the pavements too large or they will become a safety hazard. In the U.S., the joints have to be less than a half inch in public areas to conform to the Americans with Disabilities Act, Bowers explained.
"Maintenance is the key," he said, when an audience member asked if the joints could eventually be clogged with debris.
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