Abstract

Almost half of the City of Winnipeg is serviced by combined sewer systems. The service area is mainly in the older, core area of the City, and comprises approximately 10,500 ha. The combined sewer service area is partitioned into 42 individual sewer districts. Each district has its own lateral, collector and trunk sewer system with at least one river outfall.

The combined sewer systems were designed and built from the late 1800s, up to 1960, and reflect the site conditions of the time. Since then increases in impervious area, such as paved parking lots, driveways and wider paved streets, have changed the district hydrology. This led to less stormwater infiltration and higher flows and volumes of runoff entering the combined sewer system. Consequently, the conveyance capacity of the sewer system is frequently exceeded, particularly in the older areas. This causes sewer surcharge and backup into basements, with resultant property damage and potential health risks.

The City of Winnipeg initiated a basement flood relief program in the mid-1960s to provide a minimum five-year level of protection to the residents. Since 1977, this program has been developed with computer models based on various versions of the Stormwater Management Model (SWMM). To date, sewer relief works have been implemented in 21 of the City's combined sewer districts. These relief works have been carried out, for the most part, in isolation from other City initiatives. The current climate of fiscal responsibility, heightened public awareness and the introduction of new City infrastructure initiatives mandate a thoughtful and carefully planned program, fully cognizant of current and future planned development in all public sectors.

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