Blue roofs capture and reuse rainwater, instead of letting it flow into municipal sewers. They can reduce the amount of pollution entering our waterways and help us better manage intense storms. They can make life easier and less costly for residents and municipal governments as we experience the effects of climate change. Dealing with stormwater is a growing problem for municipalities. Cities such as Mississauga and Brampton are no exception.
Why is stormwater runoff such a problem for cities?
Without urban development, the water cycle follows a certain pattern. Rainfall first hits plants and trees, where evapotranspiration sends it back into the air. When plants and trees can’t hold more water, rainfall reaches the ground, where it either evaporates or seeps into the soil. Heavy rainfall events saturate soils, causing water to collect and to flow downhill as runoff.
When vegetation and loose soils are replaced with houses, roads and other hard surfaces, we drastically alter this cycle. With less vegetation to absorb rainfall, less evapotranspiration takes place and more water reaches the ground. Hard, impervious surfaces that dominate urban areas (compacted soil, roads, roofs, and so on) keep water from filtering through the soil. Instead, rainwater collects and runs downhill, becoming stormwater runoff. The more impervious surface, the more runoff.
Stormwater runoff: flood risk, water quality, and negative ecological effects
High volumes of runoff cause several problems. First, it raises flood risk. Most flooding events in Ontario are flash floods. When lots of rain falls quickly, it can overwhelm municipal sewer systems. When this happens, flooding may occur, as it did in Mississauga in July 2013 and March 2017.
Second, runoff is often polluted. As it flows over roofs, roads and parking lots stormwater collects harmful pollutants – gas, road salt, phosphorus, and heavy metals, to name a few. These pollutants end up in our lakes and rivers and cause problems for both people and ecosystems.
Third, it has negative ecological effects, resulting in urban stream syndrome. When too much water flows through a river in a too short a time, it changes the river’s structure. Urban rivers are wider, flatter and have less tree branches, logs, and riffles, and their banks are often armoured with rocks to prevent erosion. This leaves less habitat for aquatic wildlife. Also, stormwater runoff is often quite warm, which changes the type of ecosystems found in urban streams.
CVC’s Integrated Water Management Team
Our Integrated Water Management (IWM) team works with municipalities and partners across the Credit River Watershed on Low Impact Development (LID) stormwater management practices. LID helps to restore the natural water cycle by filtering, storing and returning stormwater to the ground as closely to its source as possible. To do this, we use bioretention, permeable paving, green roofs, soakaways, rainwater harvesting and other tools. We’ve helped with dozens of LID practices across the Credit River Watershed.
CVC and the Region of Peel recently received funding from the Federation of Canadian Municipalities to examine the possibility of building a “smart blue roof” at our head office. This grant is through the Federation’s Municipalities for Climate Innovation Program.
We’ll look at retrofitting our existing flat roof into a smart blue roof, with real-time controls, for holding stormwater over an extended period of time. A network of interconnected sensors and real-time controls will let us save more water for future use and keep pressure off municipal sewers during storms.
We hope to build a demonstration roof so that industrial, commercial and institutional buildings can adopt blue roof technology in the future. Industrial, commercial and institutional lands usually makeup 20-30 per cent of the total urban area, so there’s a great opportunity to reduce runoff.
If you’re interested in managing stormwater on your property and live in the Credit River Watershed, CVC can help! Learn about our Your Green Yard program.