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Water Today Title December 9, 2018

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Updated 2017/4/22
Floods



EXPERTS WEIGH IN ON OTTAWA, TORONTO FLOOD PLANNING


By Ronan O'Doherty


Ontario's flood planning differs from other provinces in as much as it delegates responsibilities for floods to individual communities as opposed to handling it at the provincial level.

Below we examine flood preparedness for Ottawa and Toronto, two of the provinces larger cities, by speaking with regional experts.

An unusually wet first couple weeks of April has had those living along the Ottawa River quite concerned.

According to Manon Lalonde, Executive Engineer for the Ottawa River Regulation Planning Board (ORRPB), the region received as much precipitation in the first two weeks as it normally would during the entire month of April.

The freshet, which is commonly used to describe the spring melt season, had the ORRPB sending out a caution to locals as recently as this past Tuesday warning that low lying areas might be flooding soon.

"(On Thursday) there was a forecast for heavy rainfall but it turns out we didn't get as much precipitation," Lalonde said, "So that's good news, especially for the low lying areas in Gatineau and Ottawa."

She explained that town officials were keeping a close watch on the situation.

"However, now that the sun is out and we've had less precipitation, we're all smiling because we're seeing that the water level will stabilize," Lalonde said.

According to ORRPB, next week is scheduled to see five days in a row with no significant precipitation, which will give time for the Ottawa River system to rid itself of excess water.

After that, they'll be planning for an increase in water levels from the snow melt in the north of the watershed.

"We have large reservoirs to contain the snow melt," Lalonde said," And we do integrated management of the flow from these reservoirs."

She noted that the reservoir owners and managers communicate and analyze the results together to decide how best to hold and release water in order to minimize risk of flooding downstream.

In the meantime, ORRPB will be updating their website, ottawariver.ca, on a regular basis with forecasts on the level and flow for the following day and a half.

Toronto doesn't have quite as predictable a flood season as the nation's capital.

Rehana Rajabali, is the Senior Engineer, Flood Risk and Communications for Toronto and Region Conservation Authority (TRCA). Her organization works with the municipality throughout the entire cycle of flood management.

She said that for prevention and mitigation, there is a lot of effort spent by authorities in defining the risk area. This can mean everything from flood plain mapping to taking hydrologic models to determine what the riverine flood risk is.

This goes hand in hand with land use planning, to ensure building is done outside the zones where risk is high.

"In some places where there's a historical risk, we undertake projects to build berms and dams," Rajabali said, "However, we try to use land use management as one of the primary tools to keep people away from risk and leave room for the river to be a river."

Around the Greater Toronto Area, they use Hurricane Hazel as the worst case rainfall scenario. This was a once-in-a-century storm that smashed through Toronto in 1954 with winds that reached well over 100 kilometres an hour and as much as 200 millimetres of precipitation falling every 48 hours. 81 people died and around a billion dollars of today's money in property damage occurred.

Three years after Hurricane Hazel, four conservation authorities came together to form the TRCA.

"For preparedness we have a team of flood duty officers who are on call 24/7," Rajabali said. "We monitor weather conditions, watershed conditions and how saturated the ground is and then if we see a risk of flooding, we issue a flood message to our municipal partners, school boards, emergency services and media as well as post to our website and twitter for the public to access."

In the event of a debilitating storm, TRCA controls two dams; the G.Ross Lord Dam, near Finch Ave. and Dufferin St. in the Don River watershed, and the Claireville Dam, near Hwy. 427 and Finch Ave.

"In the Toronto region there are nine watersheds with many branches," Rajabali said, "Only two of the branches really have flood control structures on them as dams are highly expensive and ecologically they have a lot of impact," adding, "These branches are where it made sense as a solution."

After an event, TRCA slowly releases the water back into the watershed.

Their role doesn't end there however. They will also reach out to the community and gather as much information as they can in order to better prepare themselves for the next storm.

Rajabali said that currentlyTRCA's education department is working on coming up with a curriculum on flooding and emergency preparedness.

As for how Toronto differs from Ottawa, Rajabali said that its watersheds are steep and short, so when it starts to rain, it doesn't take very long for the rivers to inundate.

It can be just a matter of hours.

She pointed to July 8th 2013, when a summer thunderstorm dropped over 100mm of rain on the city.

"It didn't take long for it to spike our water level," she said, "By contrast in (places like) Calgary, you could look upstream and see what's happening in the little communities to prepare for a flood coming."

In Toronto the risk area is distributed throughout the entire watershed and flooding can happen any time of year, not just the spring snowmelt.

"We're out of ice jamming risk, and snow melt risk but we're headed into thunderstorm season," Rajabali said, "I can tell, you we keep watching and keep monitoring."












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