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Confirming what city engineers have said they suspected, a detailed report on the July flooding in and around Kanata says the basic problem was sewer pipes that were too small to handle an extraordinary deluge.
The report, dated December, takes a reckoning of each flooded basement and washed-out culvert between Glen Cairn and Carp village and after a major rainstorm last July 24. In some cases, water simply leaked in through foundations or ran in through basement windows because natural flows into creeks and the Carp River didn’t move water away from houses fast enough. In others, a more complex chain reaction was involved — such as excess water running into sanitary sewers through manhole-cover ventilation holes, leading household sewage pipes to back up and float toilet waste into people’s basements.
But the overriding problem, according to the report, was that “The rainstorm exceeded the design capacity of the existing stormwater infrastructure in Stittsville, Carp and Kanata, overwhelming the conveyance capacity of the stormwater systems in the affected communities.”
After flooding in some of the affected areas in 2002, the report says, the city focused on improving surface drainage into the Carp River and improving the river’s flow to keep water moving toward the Ottawa River. But that wasn’t the problem in 2009, the report says; it was pipes that couldn’t handle all the water that was directed into them.
The report also notes that most of the problems with washed-out culverts (short, large-bore pipes that let water pass under roadways) in the area began with joints where older culverts were extended as the roads above them were widened.
The document is the second part of a five-phase city process meant to solve the west-end flooding problem; the next is to propose and consider possible solutions. Councillors have suggested everything from tearing up and replacing the existing stormwater pipes with biggers ones to building a big stormwater storage tank under a park in Glen Cairn.