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River Flooding

One of the prime mandates of the TRCA is to reduce the risk to life and damage to property by providing local agencies and the public with notice, information and advice so that they can respond to potential flooding and flood emergencies.

Facts about River Flooding

One of the prime mandates of the TRCA is to reduce the risk to life and damage to property by providing local agencies and the public with notice, information and advice so that they can respond to potential flooding and flood emergencies. In fact, Conservation Authorities were first founded in the mid-1940s and the Metropolitan Toronto and Region Conservation Authority was formed in 1957, shortly after Hurricane Hazel caused devastating damage in Southern Ontario. Today, floodplain management is practiced across Ontario which restricts development within the floodplain and helps to reduce the risks associated with flooding. However, there are 1,000s of flood vulnerable structures located in the floodplain, either because they existed prior to current floodplain management practices or they were built under special policy provisions.

Facts of Interest:

  • There are 9 watersheds within TRCA's jurisdiction. A watershed includes all of the lands draining into a river system and, in the Greater Toronto region, ultimately into Lake Ontario.
  • TRCA's watersheds are "flashy", meaning that when rain falls on the ground it travels overland and reaches the rivers quite quickly. Therefore, water levels within the rivers can also rise quickly.
  • Flooding is caused by a combination of the amount of precipitation and the characteristics of the watershed (percent impervious surface, soil type, slope etc). The water levels in the rivers are expected to spill out into the floodplain at least once every year in urban systems.
  • The highest amount of runoff in TRCA's watersheds occurs when precipitation during winter and spring is combined with the runoff from melting snow.
  • Watershed characteristics, such as the rate at which water can be absorbed into the ground and the conveyance capacity of the rivers, can change when land is developed leading to increased risk and frequency of flooding.
  • Rivers are constantly changing (continuously eroding material from their banks and depositing sediment downstream).
  • Rivers may provide both environmental and recreational functions.
  • Throughout the last century flooding has been one of the most costly disasters in terms of both property damage and human casualties.

Safety Tips Around Flooding Rivers:

One of the greatest risks to human life and property is flooding. People, especially young children, fail to recognize how even little depths of water and/or currents can create a large hazard. Flooding is a natural and inevitable part of life, especially within areas that contain rivers and that are continually being urbanized. Urbanization can increase runoff 2 to 6 times more than it would under natural conditions. High Water Safety Bulletins, Flood Advisories, Flood Warnings and Lake Ontario Shoreline Hazard Warnings are the four types of messages issued by the on-call Flood Duty Officers. For more information on what these messages mean please click on the appropriate links. Make sure you know what to do during a flood emergency by considering the following:

  • Do not attempt to rescue friends or pets from the river if they fall in because you may also be overcome by the force of the river. Call 911 for help immediately.
  • Know if you live within a flood risk area.
  • Make sure that you have a personal 72 hour survival kit ready for yourself and each member of your family in case you have to evacuate your home or shelter "in place", meaning to use your home as a shield from hazardous outdoor environmental conditions.
  • Learn to be aware of the conditions at and near the rivers. Pay attention to rising water levels and floating slabs of ice.
  • Always respect the power of water and exercise extreme caution around it.
  • Stay at least 3m (10ft) from the edge of the river during rain events.
  • Always have an adult or a friend present when walking or playing near a river or any other body of water.
  • It is important to always wear the approved safety equipment such as a life jacket when playing around water.
  • Watch for obstacles, debris or holes that could have been formed during flooding events.
  • Be aware of the dangers of receding levels of water.
  • Be prepared for disruptions to essential services and transportation.
  • Listen to media reports for flood conditions prior to going out near rivers.
  • Never swim during a rainfall event. After the event, check the water conditions (water depth, debris and location of rocks etc.) prior to going in the water.
  • Be careful when walking near bodies of water as frozen banks and/or soft banks along the rivers can be slippery.


It is important that we are all aware of warning signs in and around our community and adhere to these warnings for our safety.