September Cool Drinks: Rain Gardens & Other Green Infrastructure – Approaches to Manage Storm water
At the first Cool Drinks of the 2016/17 season, we learned how green infrastructure, particularly rain gardens, can help to reduce storm water runoff and flooding in order to minimize damage to our local ecosystems and community infrastructure. Kyra Smiljanic opened the event by leading us on a tour of the rain garden at Pauline Johnson School in West Vancouver, a project that Kyra co-chaired. Then Amy Greenwood of the Fraser Basin Council and Steve Conrad of SFU discussed the impacts of storm water on ecosystems and infrastructure in addition to green approaches to limit run off. Joanna Ashworth of SFU ended the evening by introducing a potential rain garden pilot project for the North Shore, which would educate community members on the benefits of rain gardens, provide resources to help design and construct them, and foster community engagement. Summaries of Amy’s and Steve’s formal presentations are provided below.
Amy Greenwood, Fraser Basin Council
About one third of the country’s population resides in Toronto, Montreal and Metro Vancouver. The impacts of this urbanization on our waterways and riparian areas are significant. In urban regions where there is less vegetation near streams and more impervious land surfaces, peak water flows following considerable rain leads to greater runoff and frequency of flooding especially as erosion and sedimentation increase in streams. Water runoff from impervious surfaces like streets and driveways also carries pollutants (e.g. oil, copper and silt) into watersheds and oceans, which negatively impacts our freshwater and marine ecosystems. According to Amy, runoff in urban areas is currently 55% while infiltration is 15%. In natural areas, levels would be 10% and 50% respectively.
Green infrastructure like rain gardens and bio-swales capture and filter large volumes of runoff, thereby reducing flow and pollutants and better protecting species. These green approaches are also more cost effective than replacing municipal storm water infrastructure and provide opportunities for community interaction.
Local governments in Metro Vancouver and other regions are now beginning to incentivize this type of infrastructure. Development bylaws are requiring source control, erosion control and sediment containment. Watershed scale planning is also being incorporated into high level planning documents.
Steve Conrad, Simon Fraser University
Sewer systems that receive storm water as well as wastewater from homes and commercial establishments have control devices that divert normal flows to sewage treatment plants. If there are excessive flows from storm water runoff, the devices can become overwhelmed leading to some waste water entering rivers and streams. Similarly, open storm water only sewer systems can discharge ground pollutants along with water runoff directly into waterways. In both cases, water quality in our natural environment can be threatened. Besides this concern, storm water infrastructure may not be able to remove the extra volume quickly enough during periods of heavy rain resulting in flooding on streets.
Minimizing water volume using green infrastructure can be a viable alternative to traditional systems and detention methods. Steve recommended a number of green strategies including rooftop gardens, rain barrels, rain gardens, permeable land surfaces, wetlands and retention basins. In addition to these alternatives, storm water could also be separated from sanitary waste water.