Untitled Document

Culvert repair on Idaho 71 restores Brownlee Creek flow

Roy Grossen of ITD’s Council Maintenance shed discovered a natural wonder while supervising the repair of a culvert serving Brownlee Creek under Idaho 71 northwest of Cambridge last month.

The river channel passes beneath the roadway embankment in a 12-foot wide, 125-foot long half culvert resting on concrete footers. The two long concrete footers hold up the metal culvert. The floor of the channel was rock (riprap). The concrete footers (holding up the metal culvert that holds up the embankment that holds up the road) appeared to be primarily supported by . . . air.

A flood a couple of seasons ago flushed out the riprap from the upstream two-thirds of the culvert. Scour also had undermined the footers.

Tom Haynes, ITD District 3 Maintenance project manager, said that somehow there didn’t appear to be excessive settling yet, which was good because settlement and a collapse would wash out the embankment, severing the road between Brownlee Dam and Cambridge.

Brownlee Creek flows year-round, so repairs were made during low-flow conditions. The repairs were made even more timely because flows were increasing and winter conditions were approaching.

Haynes said only a couple of rocks supported each footer and those were left in place. He added that additional rock stacks may have been added by the contractors’ crew. “It may not have made any difference, but it was just spooky in there,” Haynes explained.

After construction of a diversion dam and pipeline, the culvert was dried and inspected. Western Construction, Inc., of Boise, completed the $196,000 repair. Western constructed new support for the footers with fiber reinforced shotcrete. The riprap floor was reconstructed with hand-placed riprap delivered by a small front-end loader.

“Western provided a significantly better product at less cost and got the job completed early,” said Haynes. He added that “Western was careful and conscientious throughout the project.”