Natural Stormwater Infrastructure
And the need to adapt to Toronto’s changing climate
Historical data has shown that temperatures in Toronto have increased by 1–1.5 degrees over the last 30 or so years. Toronto today has 10 more days above zero than it did 40 years ago. In Toronto’s context, these rising temperatures create more moisture in the air and increase the rate of rainfall. Meanwhile, the extent of urbanization has replaced natural absorption with impervious parking lots, roads, and roofs putting greater strain on human-engineered systems and decimated natural watersheds. In 2008, it was estimated that Ontario had a stormwater infrastructure deficit (rehabilitation/replacement, upgrades, and new build) of over $6.8 Billion. That is the last estimate. Toronto can expect a further 12% increase in spring/summer precipitation and 20% increase in winter precipitation by 2050. Combined with warmer winter temperature, major flooding events are set to become a year-round phenomenon. When much of Toronto’s stormwater sewers were developed, what the engineers understood as a “100 year flood” now occurs on average every three years.
There are obvious and proven alternative measures to ease the threat of stormwater and adapt to the future- natural infrastructure. Natural infrastructure, such as bioswales channel, filter, clean, and absorb stormwater much more efficiently than sewer systems while having the added benefits of beautifying the city and increasing access to native plants in urban settings, which has proven mental health benefits.
Beyond creating space and refuge for birds, bees, butterflies, and other insects, bioswale infrastructure has proven proven to be key to reducing flash floods and pollution in runoff. Native plants selected into a so-called “rain garden” are generally 30% more absorptive than a patch of lawn, let alone concrete. These highly absorptive native plants are part of a larger system that constitutes the bioswale. The bioswale allows around 25% of water to be absorbed deep into the ground, which is important to retain and replenish the water table. Another quarter of water is absorbed into the shallow ground, feeding the plants. 40% of the moisture typically evaporates, which creates natural cooling that combats the urban heat island effect. Only 10% of water will continue on as rainwater. However, this remaining runoff will have the chance to be cleaned by the plants in a natural process to remove heavy metals, road salts, oil, bacteria, and pesticides. In road design, bioswales can connect to the sewer system and collectively share the responsibility for stormwater management in the instances of localized floods. A focus on native plants also reduces the need for mowing and trimming, which creates both a reduction in pollution emitting devices and a reduction in maintenance costs.
Natural infrastructure has been proven to be a better investment in the short time compared to sewer systems. Bioswales are three to six times more effective per $1,000 invested than conventional stormwater management systems. Despite this, the greatest economic benefit to stormwater retrofitting is reducing the future financial burden of responding to increased extreme flooding events. The 2013 flood in Toronto resulted in nearly $1 billion in insurance claims and cost the municipality $65 million. Flooding in 2017 cost the city 15.83 million to repair plus lost revenues including over six million dollars in ferry fees alone when Toronto Island closed. Maintaining outdated stormwater management systems that are failing in our current climate, without consideration for the future climate is poor environmental and fiscal management.
There are also proven health benefits to being active in natural settings. In fact, there are proven mental health benefits to just seeing nature. It is a phenomenon that has been observed many times in hospitals among patients that have a view of nature. By bringing native plants into heavily urbanised areas, not only is the harshness of the concrete environment softened but there is more equal access to natural processes that benefit people’s well-being.
Dynamic problems such as a changing climate, mental health, and municipal financial constraints necessitate dynamic solutions. Our streets of concrete and asphalt need to soften and absorb a significant amount of rainwater in order to avoid a multi-billion dollar bill to taxpayers, to create new access to plants in the city and reap the mental health benefits in our densest and least green neighbourhoods, and filter pollutants that are contaminating water systems and ultimately hurting Lake Ontario. Toronto has 5600 km of streets accounting for about 25% of the entire landmass of the city. These streets need to lead a great adaptation to accommodate green retrofits and natural infrastructure to mitigate the changing climate and create a healthier city.