Mississauga hammered again, four years after last disastrous storm

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There were deep sinkholes on residential streets, hundreds of flooded basements and storm sewers that gushed water with such high pressure that manhole covers popped off.

Mississauga was perhaps the hardest-hit part of the Greater Toronto Area in Monday night's storm with 126 millimetres of rainfall recorded at Pearson International Airport (compared to 97 mm recorded in downtown Toronto) – hammering a city that has spent the four years since its last disastrous storm scrambling to bring its stormwater infrastructure up to snuff.

"The amount of rain we got is above design standards," said Martin Powell, the city's commissioner of transportation and works. "Often they talk about designing to a Hurricane Hazel-type storm. Our records have shown that … we exceeded that type of storm."

In December, city councillors approved a new levy for stormwater management as a way of dramatically increasing the funds available to complete projects such as building retention berms and replacing storm sewers. A study completed by Michael Gregory, a water resources engineer with consultancy firm AECOM, found Mississauga's existing funding source for stormwater management – a combination of property taxes and development charges – wasn't enough to maintain and improve the system.

The levy – which would be roughly $95 per year per household – is projected to raise $27-million per year for the city.

While Mississauga spent $14.7-million in 2012 to maintain its stormwater system, Mr. Gregory's report said it would need to spend nearly $40-million each year to bring it to a "sustainable" service level.

The levy will still take more than a year to roll out as the city decides how to administer it, said Mississauga Councillor Bonnie Crombie, whose east-end ward was the worst hit in the city, given that Etobicoke Creek runs through it. Ms. Crombie spent much of Tuesday on the road in her ward, surveying the damage on regional streets and in residents' homes.

"One gentleman said he turned over because his mattress was wet and he turned over to get up and he stepped into knee-deep water," she said.

While much of the water has receded, cleanup is just beginning: The city must tend to major road erosion and property damage.

When the rain started coming down in sheets along Cooksville Creek in central Mississauga during Monday's rush hour, it was déjà vu for residents who'd seen this four years ago. The 67.6 mm of rain that pelted the city on Aug. 4, 2009, caused extensive flooding and prompted the city to form the Cooksville Creek task force to find ways to prevent such devastation in the future.

Mr. Powell said the city has begun rolling out various projects to address flooding with Cooksville Creek (such as building berms), but some will take many years and millions in funding to implement. A retention pond north of Highway 403 would have the greatest impact on preventing flooding, he said, but is now at the very start of the environmental assessment stage and after that will move to approval for funding. It's a long way from realization.

Mr. Gregory said even though ponds or pipes may be developed with a long service life (in Mississauga's case, 100 years), that only speaks to how long they'll maintain their structural integrity – not necessarily what volumes they can handle.

"We just can't build pipes to keep people's feet dry for a [once-in-100-years] event," he said.