Smithfield staff recommend upsizing Second Street culvert; Fourth Street fixes would require property acquisition

Engineers hired by the Town of Smithfield recommended the town move ahead with design and permitting to enlarge the culvert under Second Street to reduce frequent flooding, while noting that meaningful mitigation at Fourth Street would require property acquisition or easements and significantly higher cost.

The study presented to the Town Council by Perry Ross of Withers and Ravenel analyzed Spring Branch, a FEMA-studied stream with about a 700-acre drainage area that runs through downtown and discharges to the Neuse River. Ross said the firm modeled 2-year, 10-year, 25-year and 100-year storm events and focused on reducing inundation for the 2- and 10-year storms because the larger events are dominated by backwater from the Neuse.

The study found Second Street acts as a downstream bottleneck. Existing conditions include a 65-inch corrugated metal pipe under Second Street. Ross summarized three reasonable options: adding a 54-inch overflow pipe adjacent to the existing pipe, replacing the culvert with a concrete box culvert, or replacing it with a structural arch-type metal culvert. "They all offer significant drops in flooding immediately upstream of Second Street," Ross said, pointing to model runs that showed 2- and 10-year backwater reductions in the range of about 5.2 to 5.9 feet depending on the alternative. He also…