Why do manhole covers explode in heavy rain?

The thunderstorms that swept through the greater Montreal area on Thursday evening caused a deluge with rainfall of 40 mm to 60 mm in less than three hours, putting a strain on the metropolitan infrastructure.

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Blue subway line completely stopped, other lines stormed, streets flooded, shafts unlocked, basements flooded, the list of consequences is long.

For the spokesman for the city of Montreal, yesterday’s situation is exceptional.

“We had 70 and 50 mm in the west of the city. A difficult situation, very difficult,” explains Philippe Sabourin in an interview on the program Le Québec Matin.

“The aqueduct network in Montreal, particularly in the center of the island, has been consolidated. Sewage and rain are sent together to the treatment plant.”

If the city manages to drain 99% of the rain that normally falls, the grid was literally overloaded yesterday.

“Yesterday, 50% of the water had to be channeled into the banks. It works a bit like your bathtub. If you forget to turn off your tap, the water will overflow. That’s how it works,” explains Mr. Sabourin.

About 40 houses were damaged by the sewers. Owners can apply to the city.

Several videos showed manhole covers literally flying through the air under the pressure of the water. What causes such a phenomenon?

“It is the force of the water that enters the sewer pipe and propels the air. The force is so great that yesterday, at least in two places, the swampheads didn’t resist”, specifies Philippe Sabourin.

He gives confidence for the future: The city is building new retention basins to collect and store rainwater and to avoid such backwater phases.

“Thanks to the existing basins, we have treated as much water as possible, but of course there will not be zero risk. This is no reason to reduce our efforts, on the contrary.

In addition to the retention basins, natural pits are being dug in the streets to collect all the rainwater, which can be a major headache for citizens.

In addition to the heavy rain, 4 to 6 cm of hail fell in Lachute and Deux-Montagnes, Environment Canada adds in its weather summary.

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