Abstract

Current Provincial criteria requires stormwater quality control for all new development. Traditionally, this requirement has been satisfied by the implementation of individual stormwater management facilities for each future development site. For urbanizing watersheds, the application of the currently accepted approach would result in numerous, broadly distributed facilities. Operations and maintenance required for the multiple scattered systems would be costly. Moreover, since the stormwater control systems would discharge to the existing storm sewer system, which historically has had essentially no quality control, any benefits to treating the runoff on-site would be largely reduced by the mixing of the treated runoff with untreated stormwater within the storm sewers.

The requisite stormwater quality control could alternatively be provided by centralized stormwater quality controls located at, or near, the storm sewer outlets to the receiving watercourses. This approach would reduce the operation and maintenance costs compared to multiple on-site facilities, and would provide more efficient and effective stormwater quality control. This chapter presents a design approach, applying continuous simulation, to determine the off-site storage required to provide the requisite stormwater quality control for the scattered future development areas. The Upper Ottawa Subwatershed in the City of Hamilton is used as a case study for the application of the design approach described herein.

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