Most pavement is impermeable to water. As a result, paved surfaces need to be designed to funnel water into drains, and drainage and sewer systems need to be designed for the high capacity necessary to deal with runoff from the huge number of paved surfaces in our cities. Instead of replenishing groundwater, precipitation is redirected to rivers and lakes. Runoff from roads carries with it automotive pollution, which is then concentrated in downstream bodies of water.
Various technologies are coming into use, however, for pavement that is permeable to water. Porous asphalt and pervious concrete are fairly new techniques, so they are still being developed and improved. The main difficulties include weight resistance and longevity, as well as cold climate installation. And, of course, it’s more expensive to install (particularly for cold climates), though it may be cheaper than conventional pavement if considered together with the costs of storm-water management.
What’s the point? First off, urban runoff is reduced, and with it pollution and the need for large and extensive drainage systems. But there are other benefits that I haven’t seen mentioned elsewhere. On impervious road surfaces drainage can work poorly, leading to the sometimes hazardous accumulation of water, which could be averted by permeable pavement. Likewise, it can prevent the ubiquitous puddles that form in depressions on sidewalks and paths. This pavement can also eliminate the need for drainage grates that are often encountered on bike lanes, which can be a hazard and nuisance to cyclists. If pervious concrete is used, it has the added advantage of reflecting more sunlight than asphalt, which can have a significant mitigating effect on climate change.
The technology is promising and I am surprised that the Region of Waterloo hasn’t yet taken up the idea. The Region should investigate permeable pavement and at least pilot the technology. They could do worse than paving the path through Waterloo Park as a test.