Flood Risks in Toronto

In 1954, Hurricane Hazel swept through Toronto with unparalleled force. Although Toronto is no stranger to flooding—the first written account of a flood was in 1797—many were unprepared for the devastation this storm caused. Hurricane Hazel made its way to Ontario on October 15, 1954. Within 24 hours more than 200 millimetres of rainwater had fallen over the city. The Humber River and Etobicoke Creek watershed as well as Holland Marsh were the most affected bodies of water. These areas began to overflow and an excess of rainfall destroyed communities, roads, parks and public utilities. As a result of the storm, 81 people lost their lives and thousands were left homeless. It is estimated that a storm of this magnitude today would cause nearly $1 billion worth of damage.

Why is Most of Toronto at Risk of Flooding?

Urban areas are at risk of flooding because they are typically formed around lakes, rivers and harbours. Extreme weather conditions such as heavy rainfall, hurricanes, melting snow and ice are the most common causes of flooding in a city. Increased urbanization also contributes to flooding in cities. As a city develops, the ground gets covered in concrete, pavement and other materials that prevent rainwater from seeping into the soil and contribute to overflowing storm sewers. We can reduce flooding on downtown streets by creating more naturalized spaces like green roofs where rainwater can be absorbed instead of running into our storm sewers.

Flood Risk in the Port Lands

A map of Toronto that shows the area at risk of flooding from the Don River shaded in blue.
This graphic shows the 290-hectare area currently at risk of flooding from the Don River.

Toronto and Region Conservation (TRCA) has mapped out the areas in our city most vulnerable to flooding. Knowing which areas are at risk can help us determine where to build new homes and businesses. The parts of our city that were developed before the region’s floodplains were mapped out must find ways to lessen their chances of flooding. The Port Lands and surrounding communities is one such area. The Port Lands was created overtop of former wetlands. This was the natural mouth of the Don River. During a major storm, excessive water could safely flow into Lake Ontario. When the Port Lands were created in the mouth of the river, this natural greenspace was replaced by concrete. Now, during a major storm, this entire area could be overwhelmed with water that comes rushing down the river and overwhelms its capacity.

That’s why the Port Lands Flood Protection Project is so important: 290 hectares of Toronto’s southeastern downtown currently sit in the floodplain of the Don River.

Once flood protection is complete, a vast stretch of land within a 15-minute bike ride from central downtown will become a place where we can build new homes, public spaces and parkland, allowing the city to expand in a sustainable way.