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TRCA Flood Management Program

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The Flood Management Service was established in 2011 to bring together a dedicated team with expertise in water resources engineering, risk and data management, hydrometrics, infrastructure and project management. The Flood Management Service works to fulfill one of the principle mandates of the TRCA, which is to reduce the risk to life, and damage to property, due to flooding.

During extreme weather events the Flood Management Service works closely with local government agencies (within Durham, Peel, Toronto, and York Regions), Environment Canada's Weather Office, and the Ministry of Natural Resources to provide notice, information and advice so that effective emergency response procedures can be enacted.


  • Provide clear and consistent flood warning messages through our 24/7 Flood Forecasting and Warning program.
  • Produce long term plans for the sustainable management of flood risk within TRCA's jurisdiction.
  • Develop state of the art flood forecasting technologies (e.g., NexFlood).
  • Identify flood vulnerable areas and undertake mitigation measures to reduce that risk.
  • Disseminate information about known flood risks and preparedness, through an outreach program for the public and municipalities.
  • Operate and maintain flood control infrastructure across the GTA, including large dams, channels, floodwalls, berms/dykes etc.
  • Collect, interpret, and disseminate information about water quantity, water quality and meteorological data through our hydrometrics program.


The TRCA's Flood Management Service has been developed in order to prepare and respond to our changing environment, the needs of our municipal partners and the health and well-being of The Living City by utilizing the 5 pillars of emergency management: Mitigation, Prevention, Preparedness, Response, and Recovery.


Most flooding occurs when the volume of water in a river or stream exceeds the capacity of the channel. Flooding also takes place along lake and coastal shorelines, when higher than normal water levels inundate low-lying areas.  When rain falls on the ground it either infiltrates the soil or becomes surface flow. Surface flow rapidly travels overland and reaches watercourses causing water levels within the rivers to rise quickly. Flooding is caused by both the amount of surface run-off and the characteristics of the watershed (percentage of impervious surface, soil type, slope etc.). Due to the urban nature of the GTA much of the rainfall travels overland and causes waterlevels in streams and rivers to rise quickly. Watersheds with these characteristics are called "flashy".

In Toronto we experience large scale weather systems with long-term rainfall and short-lived thunderstorms with significant rainfall. Short-lived storms are hard to predict and can produce flash flooding from localized downpours that last only minutes. In addition, Canada is threatened by an average of six tropical storms a year, some of hurricane force. Given the devastation caused by gale-force winds and driving rain that accompany these extreme events, knowing exactly when and where they will strike is critical. For more information visit Environment Canada's Hazardous Weather page.

Climate change has resulted in a number of changes to our weather patterns including more frequent, powerful, and unpredictable thunderstorms resulting in large amounts of precipitation in short time periods. The result is almost immediate and devastating flooding. This has been challenging for the municipalities within our jurisdiction; TRCA's Flood Management Service is a crucial partner in providing information which informs municipal response to flooding. This includes updating our information as science evolves in this area.


It is important to note that TRCA's mandate addresses riverine flooding, which occurs when water levels rise and the watercourses overtop their banks.

Urban flooding is caused by the limited capacity of existing stormwater infrastructure or drainage systems. It is defined as street flooding, basement flooding, and flooding of other low lying urban areas. Please contact your local municipality to find out more information.

If you are experiencing flooding on your TRCA rental property please call the property pager number at (416) 295-0127.


Floodplain management is a fundamental practice of TRCA, which is achieved through policies that restrict development within the floodplain. In locations where the floodplain remains undeveloped, the risk to life and property is reduced. There are thousands of flood vulnerable structures located in the floodplain within TRCA's jurisdiction, either because they predate our floodplain management practices or they were permitted under special policy and planning provisions. To learn more about the rules and regulations regarding development within a flood regulated area please see the Planning and Development Services section.


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