Sourced from the Toronto Star
Paving over porous paradise, or any absorbent ground, increases the risk of basement flooding, say researchers using City of Toronto data.
Their study could help GTA homeowners make sense of the sometimes-ridiculed notion that the amount of land people cover with buildings, parking pads, parking lots and more, is linked to the costly rising tide of urban flooding that is expected to worsen in coming years.
“From what we have seen, areas with less green space — mostly developed areas, without any consideration for pervious or green areas — are more likely to have this kind of basement flooding,” says Yekenalem Abebe, a University of British Columbia engineering PhD candidate who co-authored the study with UBC civil engineering professor Solomon Tesfamariam and Golam Kabir, a University of Windsor assistant professor in engineering.
Other factors make basements prone to invasion from “pluvial” flooding — rainwater unable to soak into the ground, as opposed to “fluvial” flooding, which occurs when bodies of water overflow. They include aging, deteriorating sewer pipes and other infrastructure meant to steer rainfall away from homes. In Toronto, some of those pipes are more than a century old and, when overwhelmed by big storms, send untreated sewage from downtown into Lake Ontario.
Images of residential flooding, including Brantford in recent weeks, Toronto Islands last summer and across the U.S., are becoming more common.
The researchers didn’t get all the data they wanted while developing a “flood vulnerability index” that any city can use. But even if they had, Abebe said, “I would still expect pavement and impervious surfaces to be one of the most important factors,” in basement flooding risk. Urbanization is accelerating the loss of absorbent ground, communities are being hit more frequently with intense storms, and costly-to-replace infrastructure is failing to handle the runoff.