US 95 Spalding Bridge over Clearwater River

Lewiston, Idaho
Scour Protection
Owner:
Engineer:
Contractor:
West Companies
Technical Description:
• 24-in. A-Jacks®
• Units: 14,982
Installation:
August 2014

The US 95 Spalding Bridge spans 1200' over Clearwater River and is a vital connection for the region. Built in 1962, the historic Spalding Bridge was identified as one of the top 10 most scour-critical bridges in the state of Idaho. Over the years, several of the bridge's eight piers became undermined, or were in danger of becoming undermined. The piers in danger required a solution to enhance stabilization and provide protection.

As the best solution, 14,982 - 24" A-Jacks® concrete armor units were installed in the high flowing water conditions. The A-Jacks units stabilized the piers, while also protecting the sensitive habitat of the riverbed's delicate ecosystem.

During the planning stages of the project, it was noted that Clearwater River was flowing at 12,900 cfs, but since the area was a sensitive habitat for several threatened fish species, which provided sustenance for the local Nez Perce tribe, it was impossible to divert the river. Since even temporarily diverting the river in a localized area wasn't an option, an alternate plan was needed. For this reason, the A-Jacks units were installed under the water with the use of an excavator on a barge and pushed by a tugboat. Modules of 24" A-Jacks units were installed in water depths ranging from 4-14' in water flow conditions of 6-12 ft/sec. The conditions at Pier 7 were the most significant with the pier severely undermined.

"A-Jacks mats were needed to shield the bridge piers against further erosion from water flow," stated Reed Hollinshead, Public Information Specialist with the Idaho Transportation Department. "Moreover, research indicates that voids in the mats provide a support system for the river gravels and help to promote fish habitat. Fish, particularly steelhead and salmon, are a vital part of the local ecosystem and needed to be protected during critical bridge safety work."

Overall, the project was completed in 29 working days and well ahead of the deadline imposed by NOAA Fisheries. In addition, there weren't any turbidity exceedances, and the cost of the project was $30,000 under the original contract amount. In 2015, the project was the winner of the 2015 AASHTO President's Transportation Award and named an AASHTO Innovative Initiative for technologies able to be used by other state transportation departments.

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