As rain fell Sunday morning, Camila Pechous woke up and checked the basement of her home in Portage Park. As she had expected, there was some water leakage but nothing major.

“We started to prepare breakfast with the kids and in about 10 minutes, the whole basement was flooded. Six inches of water,” Pechous told WBEZ’s Reset on Monday. “We lost our water heater, furnace, the washer in the laundry room is all gone, and we probably need to replace the carpets, too.”

Sue Gottchall, who lives just east of Lincoln Square, told WBEZ’s Reset that half of her building had flooded, with water coming up three sewer drains in her apartment.

“We’re cleaned up now but it took about six hours of heavy work to get the water out,” Gottchall said.

As torrential rain completely soaked parts of Chicago on Sunday morning, basements and partially submerged streets were not the only things that got flooded. Inbound calls poured into the city’s non-emergency system, 311.

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More than 1,400 complaints — of “water in basement” or “water on street” — were logged on Sunday, and there were more than 700 the following day. Most were concentrated on the city’s Far Northwest and Far North sides.

One in four of the complaints came from Portage Park.

West Ridge, Edgewater, Albany Park and Lincoln Square had the next highest volume of complaints.

The West Ridge neighborhood received more than four inches of rain, according to data from the National Weather Service. North Center got just over three inches. Meanwhile, O’Hare and Midway airports got 1.95 and 1.40 inches, respectively.

The rain fell unevenly on Sunday, inundating some areas with intense downpours while sparing others, which explains, in part, why 311 service requests spiked in some neighborhoods and not others.

On May 17, 2020, a similar rainstorm swept through Chicago, flooding the Chicago River and leaving several swaths of the city waterlogged. 311 received nearly 1,800 complaints about water rising in basements or collecting on the streets that day.

The highest volume of requests came from communities throughout the city, particularly from the Northwest Side. The five leading communities were Austin, then Portage Park, Washington Heights, Belmont Cragin and Logan Square.

311 data doesn’t capture the full picture

When residents file a complaint about a flooded street with the address of the incident and the location of the water — in the middle of the street, on the curb or in an alley — 311 then dispatches a sewer crew, according to the 311 website.

The complaint data is one of the inputs the Department of Water Management uses to determine where to improve portions of the city’s sewer system.

But not everyone calls 311 when issues arise. Some Chicagoans might not know the service exists, while others might choose not to call 311 because they don’t think it’ll be helpful to them.

Still, 311 data is one of a few data sources available that can help researchers and the city understand, broadly, the severity of storms and where they occur, said Ryan Wilson, manager of water resources at the Metropolitan Planning Council.

“Flooding happens as a result of rainfall which can be very erratic, from neighborhood to neighborhood or even block to block, and the amount of water that goes into our sewers and potentially back into our basements is really hard to predict, much less track,” said Wilson.

For Wilson and his team, 311 calls are a good way to understand how intense a rain event was, but not necessarily who was most impacted.

“That’s a very different problem when we think about equity, infrastructure and distribution of flooding impact. That’s not something where 311 data tells a really clear story,” he said.

Geysers in the street

For the most part, the city’s groundwater systems are designed to handle lots of rainfall, with mechanisms to keep water in the streets in order to restrict the amount that flows into the sewers.

But in several parts of the city hit hardest by Sunday’s storm, the deluge completely overwhelmed the system.

“The underground sewers were receiving water from a lot of different places and a combination of gravity and pressure caused the sewers to backflow into certain places,” explained Wilson. He also noted that excess debris and trash can also contribute to the backflow by clogging sewer inlets.

On some streets, including this sighting at Lawrence and Ravenswood, water also burst out of sewer manholes, shooting several feet up out of the ground like a geyser.

Wilson explained that when water rushes into “deep tunnel drop shafts” — one of the places where two sewer systems connect — rapidly, air that is normally released through built-in vents gets trapped and builds up enough pressure to force the water out from underground.

“Severely intense water inflows can entrap air which may produce the rare geyser effect seen last weekend,” said Megan Vidis, a spokesperson for the water department.

This morning at Lawrence and Ravenswood pic.twitter.com/cf22at05Ha

— Kyna (@KJintheCity) September 11, 2022

“The Department of Water Management maintains the sewer system and has replaced and lined 717 miles of it over the last decade to ensure it is operating at peak efficiency,” wrote Vidis.

“However, unprecedented rainfall events like the one last weekend which dumped approximately 4 [inches] of rain in 2 hours on parts of the city require time for the sewer system to process,” Vidis wrote.

Climate change effect

What made Sunday’s storm notable for this time of year was how hard it rained over a short period of time, said Todd Kluber, a meteorologist with the National Weather Service. In some areas of the city, rain fell between 6 and 8 inches per hour, almost double that of a typical thunderstorm.

“Those rainfall rates are actually more typical of what we would expect in the Southeast or South U.S. with hurricanes and tropical storms where they get really torrential rainfall and flooding,” Kluber said.

With climate change, one of the main concerns is that these types of storms will increase in frequency and intensity.

“Warmer air can hold more water,” said Kluber. “If we have a warmer climate later into the season, we can hold more water in the environment which translates into heavier rains.”

Charmaine Runes is WBEZ’s data/visuals reporter. Follow her @maerunes. Amy Qin is WBEZ’s data reporter. Follow her @amyqin12.