Development of a Wet Weather Flow Management Master Plan for the City of Toronto

The City of Toronto has developed a Wet Weather Flow Management Master Plan incorporating a new philosophy in wet weather flow management where rainwater is recognized as a resource. Wet weather flows are to be managed on a watershed basis, and a hierarchical approach to wet weather flow management is to be used, starting with at source, followed by conveyance and finally end-of-pipe control measures. The study area extended across the City of Toronto, encompassing six major watersheds and the waterfront. The Plan development followed the planning principles of Ontario's Environmental Assessment Act and incorporated broad public and agency consultation. A series of 13 objectives were identified and grouped into four major categories: water quality, water quantity, natural areas and wildlife, and sewer system. An innovative approach was used which integrated hydrologic, hydraulic and water quality predictions from land-based, watershed and lake models, respectively, to assess the effectiveness of various strategies. The receiving water response indicated that source controls and conveyance controls were insufficient to achieve the receiving water objectives of the Plan. This was only possible through the implementation of a comprehensive set of measures consisting of: source controls, conveyance controls, end-of-pipe controls, basement flooding protection works, stream restoration works, shoreline management, enhanced municipal operations and an enhanced public education and community outreach program. Overall benefits expected through the Plan include: swimmable waterfront beaches, control of combined sewer overflows in compliance with provincial requirements, basement flooding protection, protection of the City's infrastructure from stream erosion, restoration of degraded local streams and aquatic habitat, the reduction of algal growth along the waterfront, and improved stream water quality in area watercourses. The implementation cost of the Plan over the 25 years is estimated to be $1.047 billion with an additional $233 million in operational and maintenance costs.