When the City of Oshkosh, Wis., needed to correct flooding issues in its downtown area, conventional stormwater detention systems were deemed unacceptable because of space limitations. Instead, the City opted for an innovative underground solution using precast roof panels from County Materials that helped improve parking facilities as well.
“For a conventional aboveground basin we would have needed an entire city block,” explains city engineer James Rabe. “We looked at the area and realized that we had over two acres of parking lot (at City Hall) and we could do something underneath it.”
The plan offered the added bonus of parking facility improvement. The site consisted of two adjacent parking lots formerly under separate ownership. A complete renovation would make the lot much more functional by allowing drivers to maneuver through the entire parking area without having to exit and reenter.
The site’s high water table precluded the use of pre-manufactured stormwater collection devices. Using them would have required redirecting groundwater, which would likely cause settling in surrounding structures. Instead, the City opted for a cast-in-place detention tank.
However, the roof of the 22,500 square foot structure was not cast in place. Instead, the design team chose to top the stormwater tank with 249 precast concrete panels from County Materials. “We estimate that using the precast roof panels cut three to four weeks off the construction window,” says Rabe. The decision to use precast minimized the inconvenience of disrupted parking at City Hall, while also helping to lower project costs significantly.
The project commenced on March 4th and is expected to be completed ahead of schedule in the fall of 2013. It promises to be an elegant solution to a common urban problem. Says Rabe, “We’re utilizing land we already had without having to go out and acquire more real estate for it.”