Stormwater Strategies: Cities Prepare Aging Infrastructure for Climate Change

Abstract

If it weren’t for the cement pipe segments nearly nine feet in diameter, oversize yellow backhoes, towering piles of sand, and yawning trenches scattering the streets, the section of Toronto near the junction of Connaught and Fargo avenues would look like an ordinary residential neighborhood. In spring 2011 this area of comfortable-looking contemporary houses surrounded by tidy landscaping was a construction zone as its storm sewers, most fewer than 20 years old, were ripped up and replaced with much larger pipes. The purpose of all the disruption? To prevent the flooding of basements and garages that has plagued these homes during unexpectedly heavy rains in recent years. The area is just one of 32 across Toronto slated for storm sewer upgrades with a stringent new design standard. Whereas the old pipes were meant to capture the volume of water rushing off roofs, driveways, and streets during the kind of storm that would occur on average every 2–5 years, the new ones are tailored to so-called 100-year storms.1 These used to have a probability of occurring just once every century but now seem to be more frequent, according to Michael D’Andrea, director of water infrastructure management for the City of Toronto. “That’s an extreme design standard, no matter how you look at it,” D’Andrea says, and shoehorning the necessary infrastructure into a densely developed city like Toronto is technically challenging and expensive—especially considering that the old pipes were still well within their useful life spans. “We’re rebuilding systems in an area of the city that, all things being equal, we shouldn’t have had to worry about for several decades to come,” he says. Memphis, Tennessee, 13 June 2011: A state Department of Transportation employee works to unclog a drain on the Madison Avenue ramp onto I-240, where the flow of traffic stopped due to high water covering the road. Heavy rain and wind had pounded Memphis ... But extreme weather calls for extreme plans. City officials deemed the new standard necessary after two huge soakers, one in May 2000 and an even bigger one in August 2005, lit up the city’s switchboards with thousands of complaints of flooding and raw sewage backing up into basements. In fact, no fewer than eight so-called extreme weather events, with rainfall exceeding that of 25-year storms,2 have hit Toronto in the quarter-century since 1986. The 2005 downpour, which unleashed 6 inches of rain in about 3 hours, not only ruined basements but also damaged cars, broke water mains, washed away sections of road, flooded a wastewater treatment plant, and destroyed a sanitary sewer line, sending raw sewage into a creek.3 The Institute for Catastrophic Loss Reduction, a Toronto-based insurance-industry research institute, described it as the most expensive natural disaster ever to befall Ontario and the second most expensive in Canada, with damages exceeding Can$500 million. “There’s no denying that in this particular area we’re seeing these extreme storms more frequently than we have in the past,” D’Andrea says. “It’s basically a call into action.” Climate change is already affecting water utilities, according to a 2009 report from the National Association of Clean Water Agencies and the Association of Metropolitan Water Agencies, industry advocacy groups based in Washington, DC.4 A seemingly contradictory witches’ brew of more frequent and extreme storms, drought, and sea-level rise is beginning to stress some cities’ water infrastructure. Although managers typically think first of the effects on drinking water supplies, many are realizing that their wastewater systems (the focus of this article) also will be keenly affected, with profound potential consequences for public health. In many places, these systems are already under strain from population growth, development, underfunding, and maintenance backlogs.5 At a time when North American cities are just beginning to assess what altered long-term weather patterns may bring, a handful, such as Toronto, have already committed to upgrading their wastewater systems with climate change in mind.