UPDATE: Emergency repairs after storm sewer collapse under Monon - WKOW 27: Madison, WI Breaking News, Weather and Sports

UPDATE: Emergency repairs after storm sewer collapse under Monona Terrace walkway

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UPDATE (WKOW) -- Much of the walkway at Monona Terrace will be closed for a couple weeks because of a large sinkhole. 

It happened Saturday from the rain storm that blew through Madison on Friday night. The rain water was too powerful for an extremely old storm sewer pipe that ran under the walkway. 

The hole was about the size of a small car and engineer with the City of Madison said it was more than 14 feet deep. 

"That looks scary and dangerous," said Emma Cruz, a pedestrian that often uses the walkway as she bikes around town. 

It had several passersby looking on in shock as they passed by the gaping hole through a detour around it. 

"You usually think that everything is always working right and nothing is going to malfunction," said Cruz. 

But over the weekend, it did malfunction. The incident even shocked Greg Fries, a principal engineer with the city. 

"I have never seen this," he said. 

Fries said he believed the pipe was the oldest in Madison, possibly built in the late 1800s. The city knew it was there, but had no records of what it was made of until it collapsed. 

"It is exceedingly rare. As I said, I've never seen a pipe, and I've been in pipes that are from 1903, and they were not brick," Fries added. 

That's right, the pipe was made from old brick. Fries described how the pipe made a 45-degree angle turn and ran almost vertical. The storm water that was draining was too powerful for part of it and eroded the brick. Then, the dirt that was outside the brick pipe started entering the pipe, causing the land under the walkway to sink down, according to city engineers. 

"And pretty soon you have what we have here," he said. 

Fries said the pipe was never inspected by a camera. He notes inspections on the city's storm drain pipes aren't a top priority among other pipe inspections. 

"We are really just kind of getting that program off the ground," he said. "It's really a matter of people and equipment." 

Madison currently has tens of miles of pipes running underneath it, according to Fries. 

As for if there are other brick pipes out there that Fries may now know about, he says he's always cautious about it. But he added, a sinkhole like the one on Monona Terrace is rare to see. 

The scene of the hole will be blocked off for several weeks as the city replaces the pipe and fixes the walkway. Fries said the city will replace the drainage pipe with a concrete one. They'll won't be running it underneath the terrace, instead, it will run along the side of the state's Department of Health Services building next door. 

The city doesn't know an exact cost of the project, but one engineer says it could cost up to $100,000. 

None of the upcoming events at Monona Terrace or nearby will be impacted by the blocked off area, including Shake The Lake. 

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UPDATE (WKOW) -- The mayor's office says the storm sewer that collapsed over the weekend is located underneath the walkway connecting the Martin Luther King Jr. Blvd and Wilson Street intersection to Monona Terrace.

Emergency repairs are being coordinated and will take place this week.

The sinkhole is fenced off and fencing installed to identify allowable walk routes.

City staff are working with Monona Terrace as it prepares for a conference this week, assuring guests will have a safe passage into and out of the facility.

Shake the Lake activities will not be affected by the sinkhole.

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MADISON (WKOW) -- The City of Madison - Engineering Division says a storm sewer collapsed under the Monona Terrace walkway. 

City Engineering believes the pipe, which was very old and made of brick, began to fail after the steam tunnels under the City County Building began to flood. The earth above the storm sewer pipe then gave way creating quite a sinkhole.

Crews are working on the situation and 27 News is told it will take several days to repair.

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