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Here's why some Vancouver manholes spray water into the air

Water is sprayed out of a manhole cover on Alma Street.

With the heavy rains recently pelting Vancouver, some people noticed an odd sight.

Along Alma Street, the manhole covers sprayed water into the air. And it's not a burbling kind of water flow, it's a fine mist being shot several feet into the air, as seen in video captured by u/ThujaEphermera and shared on Reddit.

The simple explanation for this is that there's so much water in the system that it causes pressure build-up to push water and air out of the holes, which are the easiest places for liquids and gasses to escape, creating a nozzle-like effect, according to the City of Vancouver.

However, it's not quite that simple, which is why you don't see this happen everywhere in the city every time there's heavy rain.

In an email to Vancouver Is Awesome, the City explains that the age of the system, which varies across the city, factors into things, as does the increased effects of climate change.

"In this location, the pipe system is separated, meaning rainwater and sanitary water flow in different pipes," states a City representative. "The surcharge of spraying water witnessed (May 15) is occurring in the rainwater pipe system."

"When intense rain events occur, such as the rain event on Sunday, May 15, the rainwater flow in the pipe system may exceed the capacity that the pipe system is designed for, and the flow could back up into maintenance holes in the street, causing a mixture of air and water to be forced out via the vents on the maintenance hole lids."

Commenters on Reddit had much less technical descriptions of it, calling the phenomena a "forbidden spraypark," "chocolate rain" and "public bidet," though as the city noted the water is solely from the rain (though it may pick up stuff once it has hit the ground).

"I remember as a kid watching a manhole cover 'dance' on the water for 20 minutes while it was pouring rain. It just twirled around, dipped side to side, but eventually fell to one side," recalls u/anarchyreigns.

Manhole covers are designed not to fall down into the hole; that's why they're circular.