Steele County considers larger arch-pipe option after hydraulic study of Findlay Township crossing

County engineering staff on Tuesday presented a hydraulic study of a low crossing on the middle branch of the Goose River in Findlay Township and recommended installing a double line of arch pipe to reduce overtopping and downstream scour.

Mike, the consulting engineer, told the commission the existing arch pipe is roughly 109 inches wide by 86 inches tall and often is not fully used until water overtops the roadway. "Our opinion would be putting in the double line of arch pipes so that you're bigger than the existing crossing to kinda help mitigate some of those overflow times," he said, explaining the larger opening would slow exit velocities and reduce scour.

The study compared alternatives including a double line of 72-inch round culverts, an intermediate pair equivalent to 90-inch arch pipe (about an 85-square-foot waterway opening), and larger concrete box culverts used upstream. Mike said the double 72-inch round option would be cheaper for the culverts themselves (roughly $24,000–$26,000 in the county's bid-price frame), while the double-arch option would raise material cost to about $32,000 for culverts alone; installation, he added, typically increases total project cost by a factor of roughly 1.5 to 2 depending on site conditions.

Commissioners probed lifespan and local soil corrosivity, with Mike noting coatings and riprap can extend culvert life in corrosive soils. "A lot of culvert companies will tell you the last 75 years, but that's maybe a little optimistic," he said; "you should get 40." Commissioners discussed township cost-share arrangements and whether replacing with a larger pipe could set expectations for future work; one commissioner cautioned that a township could struggle to absorb increased long-term liability.

The commission directed staff to solicit bids on three options—the existing-size double 72-inch round culverts, the double arch pipe and the intermediate 90-inch-equivalent arch pipe—and return cost estimates at the July meeting. Staff also noted culvert lead times can vary and recommended ordering quickly if the board chooses to proceed.

Next steps: staff will post a bid package for the three options, gather installation estimates that reflect local trenching/backhoe and channel work, and present comparative costs and funding suggestions at the July commission meeting.