Rain Gardens

The RNS Program undertook the Rainy Day Solutions Project to examine the biodiversity values of rain gardens, looking at plant ecology and garden design from the perspective of plant associations. The project was funded by the Real Estate Foundation of BC, Mitacs and the City of Victoria. This was part of a larger study in three parts – hydrology, contaminants and biodiversity. The Civil Engineering Program at the University of Victoria is investigating water flows and the Chemistry Department will be looking at contaminants. The City of Victoria will also be examining their rain gardens from the perspective of hydrology and chemical contaminants. The Rainy Day Solutions project conducted by the RNS Program compared rain gardens as they were designed to as-built to what has survived at the sites years later. The work was conducted by a combination of both student coursework for credit, graduate student research and paid student time. One new rain garden was also created as part of the study at Oak and Orca Bioregional School in Victoria.

In undeveloped landscapes rain percolates into the ground and the water is available to add to stream flows. However, cities replace vegetation with large areas of roads and rooftops. The increased stormwater runoff from these impervious surfaces, that average 30% and are as high as 95% in downtown cores, create challenges for existing storm drains. The problem is intensified when cities densify and existing storm drains may have to accommodate runoff from more than twice the impervious surface they were originally designed to serve. Increasing the capacity of the infrastructure by installing larger pipes is prohibitively expensive. An alternative approach to dealing with increased stormwater runoff is to prevent the water from entering the pipes in the first place – to have it infiltrate into the ground instead.

Rain gardens can accommodate some of the increased volumes of stormwater and can reduce loading in the stormdrain system. Rain gardens occur in a wide range of sizes and shapes. They can be a small area on a private house property, small roadside infiltration structures (such as the Atrium Building in Victoria), small wetlands that include elements of environmental education or nature play (Oak and Orca Community School), small wetlands (BMW dealership in Vic West), larger wetlands with greater wildlife value (Fisherman’s Wharf), or elaborate structures with mechanical drainage incorporated into the system (Bertschi School’s Living Building Science Wing in Seattle).

Although the primary role of rain gardens is to reduce loading in storm drains they can also be developed as community assets. They can be incorporated into the curriculum if they are at a school. With some additional planning the vegetation used to landscape a rain garden could be designed to maximize biodiversity. Also, rain gardens can play a role in removing toxins from stormwater runoff and keep them from entering the receiving waters of streams or oceans into which the stormdrains flow. Rain gardens can be especially important in dealing with pollutants during a “first flush”, a rain event that occurs after a prolongued dry period when oils, chemicals and pet waste accumulate on roads and are in especially high concentrations in the runoff.DSCF1787



Rain Garden Report here

Case Studies here

Oak and Orca Regional School Design Process here

Annotated Bibliography here

School Grounds Report here

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