Bioretention for enhancing urban stormwater management

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Stormwater is a major source of pollution in Canadian waterways because it picks up high amounts of total suspended solids, nutrients, organic matter, heavy metals and other pollutants that are deposited on the land surface, before reaching the receiving waters. Low Impact Development technologies (LIDs) are modern stormwater management methods that can improve stormwater quality and reduce stormwater quantity. Bioretention, which involves vegetated depressions in the land surface, is one of these technologies. Since its initial use in the 90's, bioretention has seen widespread implementation but primarily in an ad hoc manner and in regions of mild and warm climates, which are atypical of most climate zones in Canada. The knowledge of the underlying processes to remove pollutants is still lacking and hence, so are the practical tools necessary for predictable bioretention design. In order to equip engineering practitioners with the confidence to use such a technology in Canada, the benefits of bioretention in managing stormwater quantity and quality need to be clearly quantified, and the practical tools for designing bioretention need to be developed. The proposed research project will combine computer modelling with observations collected on bioretention facilities developed at different sizes (spatial scales) and in two different climate zones, to answer the following questions: i) What are the underlying processes controlling the removal of pollutants (especially nutrients) in bioretention? ii) How can bioretention performance under different hydrologic conditions (such as different size rain events) and different pollutant loads be compared and evaluated? iii) How can knowledge obtained from bioretention facilities at very different scales be used to develop predictive tools? iv) How does bioretention perform under varying Canadian climate conditions? The answers to these questions will lead to the development of reliable approaches for predicting the benefits of bioretention and optimizing bioretention design. The results from this project will not only provide useful and definitive technical information on bioretention, but the practical, useful tools necessary for bioretention design.