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Sinkhole has city worried about creek seawall PDF Print E-mail
Daily News
Written by Kristyn Halbig Ziehm   
Wednesday, 10 May 2017 21:37

Revetment near Fisherman’s Park is in danger of failing without repairs that could cost $100,000

A sinkhole has opened up near the entrance to the Fisherman’s Park bridge in Port Washington — a symptom perhaps of serious deterioration of the seawall along the north side of Sauk Creek, Public Works Director Rob Vanden Noven said Tuesday.

This is the second sinkhole to have sprung up along that stretch in the last two years, Vanden Noven told the Board of Public Works. 

Daily PressLast year, a sinkhole was discovered immediately northwest of the north abutment for the bridge. City crews patched the seawall and filled the sinkhole with concrete.

“It’s been holding up,” Vanden Noven said.

But a couple weeks ago, crews discovered the newest sinkhole, he said.

“It’s a cavern underneath the sidewalk,” he said, likely caused by an opening in the seawall and scouring action by the rising lake levels.

Vanden Noven said he does not believe the sinkhole poses a problem for pedestrians using the bridge — one of the last king post truss bridges in the state.

“It’s an extremely low risk,” he said. “It’s a pedestrian sidewalk. Any settlement is going to be incremental. There would be larger signs if there were to be any type of major failure.”

The easy and temporary fix would be to have crews excavate the sinkhole and fill it with concrete to stabilize the walkway and wall, Vanden Noven said.

While that’s something city crews will do as soon as possible, he said, it’s not a permanent solution.

“Clearly, looking at the wall, it’s obviously not getting any better,” he said, showing the board members photos of the wall. “It’s all in very poor condition. The way to properly repair it is to replace the whole wall.

“Eventually the whole wall’s going to fail. Now’s the time to prepare ourselves to plan a more permanent solution.”

Vanden Noven noted that several engineering firms  are expected to be in the city next week to look at deadmen and tiebacks in the north marina slip parking lot, and he will ask them to look at the Sauk Creek wall as well.

The city only owns a portion of the seawall along Sauk Creek. Bob Pfeffer, 132 S. Wisconsin St., said the condominium owners whose property stretches west along Sauk Creek from the city land, asked if they could form a partnership with the city to repair the entire wall.

“We’re trying to avoid a total failure of the wall,” he said. “We would like to be proactive in shoring up that wall. If there’s something we could do as a joint venture ...we would be interested.”

Vanden Noven said he would seek proposals from the engineering firms that encompass the entire wall as well as just the city’s portion.

Ald. John Sigwart, a member of the board, suggested the city consider building a form along the wall and pouring concrete there. That, he said, would fill any voids in the existing concrete wall and prevent future undermining of the soils behind it, although it would not help support the wall.

“I think we have to do something now,” Sigwart said. “That hole (sinkhole) kind of amazes me, how big it is.”

Vanden Noven estimated it would cost about $2,000 for the city to excavate and fill the sinkhole, and $50,000 to $100,000 to design and build a new section of the seawall.

Work on a permanent solution likely wouldn’t be done until winter, when water levels are lowest, if funds are allocated in the 2018 budget, he added.

Vanden Noven said he hopes to bring estimates from the engineering firms to the board in June or July.