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Monday, 20 October 2014 08:53

Hurricane Hazel a turning point in flood protection 60 years ago

This month marks the 60th anniversary of one of Canada's deadliest natural disasters--Hurricane Hazel. It was the most severe flooding ever recorded in Ontario, occurring in October 1954 when Hazel passed into southern Ontario. Eighty-one people died, and damages, which included the loss of homes, bridges, and dams, were estimated at over $180 million. This led to changes that would help protect against flooding, changes that are still in effect today.

 Flooding during Hurricane Hazel
Flooding during Hurricane Hazel, Toronto, 1954. Photo courtesy of Environment Canada.

Following the devastating impact of Hazel, a flood forecasting and warning system was established. Local Conservation Authorities, in partnership with the Ontario Ministry of Natural Resources and Forestry, began providing flood forecasting services to member municipalities.

To this day, we monitor watershed conditions, including precipitation, snow cover, and flows and water levels in rivers and lakes, and issue flood messages if there is a possibility of flooding. See more about our flood forecasting and warning program.

In the event of a flood, municipalities are responsible for flood emergency response, including sandbagging, evacuation, and rescue, with the province providing additional assistance when local capacities are exceeded.

Regulations were also put in place after the hurricane to limit and control future development and inappropriate land use activities in flood hazard areas, as well as protect the wetlands that store water. Conservation Authorities are responsible for administering these regulations in their watersheds.

In our watershed, we administer Ontario Regulation 182/06, Regulation of Development, Interference with Wetlands and Alterations to Shorelines and Watercourses. Any development near water, wetlands, steep slopes, or other natural hazard lands require a permit, to ensure the safety of people and their property, and prevent new hazards from being created. See more about this program.

So, what were the factors that contributed to the Hurricane Hazel tragedy?
The amount of precipitation was extraordinary high, with more than 280 mm within 48 hours; and, the region had experienced rainy weather over the previous two weeks, making the ground saturated with water. This means the holding capacity of the soils and natural storage was already very limited, resulting in very high runoff. About 90% of the precipitation quickly ended up in rivers and streams.

The characteristics of the affected drainage basins were favorable to very quick runoff and, as a result, flash floods. These characteristics included steep watershed slopes and high channel gradients, clay soils, and a high percent of non-permeable areas because of urbanization.
At that time, there were no regulations that would control development in flood prone areas, so some of them, including floodplains, were highly developed. Many homes, cottages, subdivisions, and trailer parks were located in hazardous areas.

There was limited knowledge of hurricanes and their possible outcomes among the general public, so the warning messages that were issued were not acted upon appropriately. At the same time, public knowledge of possible flooding was very limited, as many had never experienced it before.
Over the past 60 years, we have come a long way to mitigate the potential for flooding, by keeping new development out of floodplains, improving stormwater systems, protecting wetlands that store water, and even reducing stormwater runoff on residential properties by installing rain barrels and rain gardens. When there is potential for flooding, we have advanced warning, along with a coordinated response to the flooding. Over the next decades, all of these measures will become even more important as we face increasingly erratic weather due to climate change.