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Imnaha Creek Fish Passage

Prospect, Oregon

Fish Passage






Weekly Brothers


July/August 2022

Technical Description:

  • BridgeCor® Structural Plate
  • Span: 63-ft. 8-in.
  • Rise: 21-ft. 2-in.
  • Length: 65.25 ft.

Directed by the United States Forest Service (USFS), a structure barring fish from proceeding upstream to spawn in Imnaha Creek needed to be replaced. The USFS provided AECOM, the project's engineer, with the project requirements, which included a minimum span, open area dimensions and an open bottom structure in which the natural streambed could flow.

After researching options, AECOM decided that a 63'-8" x 21'-2" BridgeCor® Structural Plate arch, 65.25' in length, was the best solution because it was economical and structurally sound. Additionally, both the USFS and AECOM were aware that plate structures have been utilized successfully numerous times for similar projects in National Forests. For the past 80 years, Contech MULTI-PLATE® has been the buried bridge standard. BridgeCor enhances the established performance of 6" x 2" MULTI-PLATE by offering nine times the stiffness and three times the strength.

In this particular application, Contech Engineered Solutions designed a custom 3 gage high strength steel BridgeCor deep corrugated (15" x 5.5" corrugations) 2 radius arch with minimum span and area. In order to fit the minimum streambed and backfill zone requirements, a rock embankment on one side of the stream needed to be removed before the new structure was installed.

In order to verify the proper shape was maintained throughout the process, the initial shape dimensions were recorded after assembly. While the structure was being backfilled, Contech provided a shape monitoring technician to monitor the shape. Once the installation was complete, the shape was measured once again in order to ensure it remained within AASHTO tolerances.

In the end, BridgeCor was a great solution for the site remaining within budget and meeting all of the requirements. All parties involved were pleased with the outcome.

“The Contech team was excellent to work with on this project," concluded Andrew Weekly, Representative with Weekly Brothers. "Contech provided the best total value for the project. The proposal process during the bid/design phase was quick and complete. The engineering side at Contech was reasonable and flexible to the project needs and our needs as the contractor. Despite poor market conditions, the ordering and fabrication process was efficient and reduced our administrative effort. Contech provided prompt service with respect to delivery, pre-installation meetings and continued support on technical matters during the installation process. The team at Contech continued to follow up after installation through final documentation and close out of the project. Contech continues to be great to work with when dealing with steel bridges, retaining walls and large plate arch structures."

This project received a "2023 Project of the Year" award from the National Corrugated Steel Pipe Association, NCSPA, in the Structural Plate category. The awards "showcase the very best projects that have been completed over the past year. Winners are announced in 13 different categories ranging from product application to steel coatings."

Technical Description:

  • BridgeCor® Structural Plate
  • Span: 63-ft. 8-in.
  • Rise: 21-ft. 2-in.
  • Length: 65.25 ft.

800-338-1122 |
Project #: 673207


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