This Note is part of a series of Notes on key City issues to update City Council at the start of its 2018 – 2022 term.

Issue description

In 2003, City Council adopted the 25 Year Wet Weather Flow Master Plan (WWFMP), with the goal of reducing and ultimately eliminating the adverse impacts of wet weather flow on Toronto’s environment. It recommended projects and initiatives for implementation within each of the city’s watersheds.

Wet weather flow (WWF) includes stormwater runoff from both overland and combined sewer overflows. Wet weather flow has historically caused degraded water quality at city beaches, impaired ecosystem health of watersheds, damaged sewer infrastructure from stream bank erosion, and property flooding during extreme storm events.

The City’s Basement Flooding Protection Program (BFPP), under the umbrella of the WWFMP, is a multi-year initiative aimed at reducing the risk of future flooding during extreme storm events. Under the program, the City is undertaking Basement Flooding Environmental Assessment (EA) studies that recommend sewer infrastructure improvements to reduce the risk of future flooding.


Over $3 billion in expenditures for the implementation of the WWFMP are identified in the Toronto Water 2017 to 2026 Capital Plan, currently fully funded from the water rate.

Currently, there are 11 BFPP EA studies underway across the City, and Toronto Water is working towards accelerating the pace of review. The purpose of these studies is to identify investments that will improve the City’s sewer system and overland drainage routes to protect the City and its residents from destructive flooding events in the future.

Lessons learned and compiled from the City’s recent flooding event of August 7th, 2018 may modify and influence the direction of the Basement Flooding Protection Program.


The WWFMP is a long-term City building initiative that contributes to a better quality of life in Toronto. The key benefits include improving water quality at the City’s beaches, rivers and streams; the protection of City assets; and reducing the risk of flooding to private and City property.

City Council approved a program management capital delivery model for the BFPP in 2014 as a result of more frequent severe storm events and widespread and recurring basement and surface flooding. The goal was to quickly and efficiently deliver a larger number of infrastructure improvements and meet the needs of an expanded program. Of the 67 Basement Flooding Class EA study areas, covering the entire city, 32 are completed, 18 are underway, and it is expected that the remaining 17 studies will be completed over the next 15 years. These studies identify improvements to the sewer and drainage system to be made within the City’s property, such as parks, roads and sewer infrastructure.

The BFPP has included the city-wide implementation of mandatory downspout disconnection and the construction and upgrade of stormwater management facilities. There have also been advances to the WWFMP’s most significant water quality improvement projects such as the Don River and Central Waterfront Project. Watercourse erosion and shoreline management studies, as well as restoration work, have also been completed to protect both City and private infrastructure. The release of the Green Streets Technical Guidelines in 2017 and the planned update to the 2006 Wet Weather Flow Management Guidelines will also improve the management of stormwater for new development and redevelopment projects across the City.

Basement Flooding Protection Subsidy Program

The City offers homeowners of single-family, duplex and triplex residential homes a financial subsidy of up to $3,400 per property (increased from $3,200 in January 2014) to install flood protection devices including a backwater valve, a sump pump, and pipe severance and capping of the home’s storm sewer or external weeping tile connection. Over 10-years, the program has distributed $36.5 million in subsidies to approximately 7 percent of eligible households in the City.

Mandatory Downspout Disconnection By-law

In 2009, City Council approved a bylaw making it mandatory for property owners to disconnect their downspouts from the sewer system, except where it is not technically feasible or where doing so would create a hazardous condition. The bylaw was implemented in three phases and is now in phase three and in-force City-wide. In 2016, Toronto Water undertook a Downspout Disconnection Field Study to assess the rate of downspout disconnection for each phase. The 2016 field study (involving 15,087 properties) found a high rate of disconnection with an average downspout disconnection rate of 79 percent across the City.

Actions or Plans

Don River and Central Waterfront Project

The Don River and Central Waterfront Project is a 25 year, $2-billion program consisting of substantial infrastructure projects that will virtually eliminate overflows from the combined sewer service area within the Don River watershed and will significantly improve the water quality in the Lower Don River, Taylor-Massey Creek and along Toronto’s Inner Harbour. Currently, $1 billion is allocated in Toronto Water’s 10-Year Capital Budget to proceed with this project.

Basement Flooding Protection Projects

The Toronto Water 2018-2026 Capital Plan identifies approximately $1.5 billion for the BFPP for the completion of Basement Flooding EA studies, the provision of subsidies and implementation of recommended infrastructure improvements to reduce future flooding. Projects can proceed to detailed design and construction where the EA study cost estimates meet the City Council threshold of $32,000 per property (at the preliminary design stage).

Efforts are underway to accelerate the completion of EA studies, and Toronto Water will report to City Council with an updated BFPP EA Study Schedule as part of the annual Toronto Water Capital Budget submission. The goal of the accelerated schedule is to initiate EA studies for all 67 study areas by 2026.

Over the next few years, Toronto Water will be installing Inlet Control Devices (ICDs) within catch basins in the City’s storm-sewer drainage systems to help alleviate basement flooding. This ICD initiative will include new communication material for residents and businesses to understand how ICDs help reduce overloading of the sewers and are designed to minimize basement flooding risks.