2024 Project Of The Year – CSP & Pipe Arch: Bigelow Gulch Fish Passage

By: Pacific Corrugated Pipe Company


A unique opportunity was presented to Pacific Corrugated Pipe Company that not only supported a meaningful infrastructure improvement but also aligned with the new “Build America, Buy America” (BABA) infrastructure law. This opportunity was in support of a large and uniquely designed fish passage which required over 40 tons of galvanized material in various sizes.

East Bigelow Gulch Road is a steep grade 2-way winding road adjacent to the Spokane River. Winter conditions resulted in excessive traffic accidents and rerouting of the road became necessary for safety. The road reroute crosses over a fish bearing stream (Aquatic Organism Passage) between two mountain sides. The final burial depth of the AOP structure would exceed 40 feet of backfill.

The primary structure was 84 inches x 623 feet of galvanized 5 x 1 pipe produced using 12 gage and 14 gage material. Manufacturing this basic structure was the easy part but the remaining design posed a bit of a challenge.

The excess burial depth of the pipe resulted in concerns from the design engineer to use traditional welded baffle methods. The baffle design was complicated, and how each baffle attached to the pipe structure was unique as well. First, the baffles required custom cutting to a specific design in order to accommodate the corrugation pitch and helix angle. Next, each of these baffle plates needed to be welded to a footer plate that required a radius matching the pipe. These plates were custom made and shaped at our Eugene plant.

After welding the baffles to the plates, the next step was to drill the holes into the footer plates to align with the 5 x 1 corrugation pattern. Once the final placement was determined, 16 additional 3/4″ diameter holes per baffle were required to be hand drilled into the pipe structure – resulting in over 1,600 hand drilled holes overall! This important step would allow each baffle to attach effortlessly into the required position utilizing the structural plate designed nuts and bolts.

Since this project included drainage upgrades, various diameters and lengths of smaller diameter pipe were manufactured to complete the project. These sizes ranged from 12 inches to 36 inches in diameter. Some diameters required almost 1000 feet worth of pipe. Finally, when adding the required fittings of the project, Pacific Corrugated produced over 2400 feet of CMP material. Today this fish passage is being used to restore and protect the local fish population.

Once again, a terrific example of a corrugated steel pipe solutions being utilized in a unique way while leaving a positive impact on our environment.