Once the clock starts ticking this spring, crews on an Oregon Coast highway project will have just 75 days to get the job done.
The U.S. 101-Fraser Creek Fish Passage Culvert Project, located at milepost 104 on the central coast, calls for workers to dig out a section of the highway and install a 105-ft. (32 m) long, 12 by 10 ft. (3.7 by 3 m) double barrel box culvert beneath it.
“When the highway was built in the 1950s, the raised elevation of the roadway created, in essence, a dam that blocked the historic tidal flow of Fraser Creek,” said Richard Little, spokesman of the Oregon Department of Transportation. “This project will restore the tidal flow and the natural estuary wetlands, benefitting endangered Coho salmon and other species in the important coastal river system.”
The original plan called for a single diversion lane with 24/7 flagging, which was expected to be a challenge in the area that sees an average of about 3,000 daily trips. Just a mile south, the traffic volume jumps to 13,500 to 15,000. But contractor LaDuke Construction LLC, of Talent, Ore., was instead able to devise a plan that will divert both lanes of traffic and eliminate the need for lane closures or flagging.
Work on the diversion lane is already under way, with trees removed and the site graded. The U.S. Forest Service, the lead agency on the project, has stockpiled the trees to use as habitat. Construction on the culvert is set to begin May 1 and finish by mid July.
“There’s very strict construction time requirements,” said Ken Kohl, ODOT project manager. “We have somewhat conflicting requirements depending on which side of the highway we are working on. In-water work periods are more tidal influenced. The east side of the highway is more of a river system. We have slightly different work periods. In-water work periods are typically early summer. We’re telling them when they can get in there and work in the water and they still have to isolate it. Out of water work we can do anytime. However, you still have the challenges of the weather on the coast and the particular soils.”
Ideally, crews would do the work during the summer at low tide, Kohl said. But environmental restrictions won’t allow that.
“Environmental permits regulate when you can work on streams based on what the fish are doing. So we’re trying to mitigate those conditions as best we can.”
The $1.37 million project calls for crews to dig at least 8 ft. (2.4 m) below the bottom of the stream channel, then fill in the culvert with 3 ft. (.9 m) of rock and bedding to be more fish friendly.
“The soils are not ideal,” said Kohl. “Historically, the soils are not very suitable for building much of anything. The mud flats you deal with are very soft. A lot of times you have to go very deep to find competent soil. We have to cast in place the box to make sure we can adequately deal with the subgrade and provide for a stable foundation to put the road back on top of the box.
“We’re having to spread the load of the highway onto the soils. We can’t just build steep side slopes. We’re removing excess material below the culvert and putting back base material, rock material that will better hold up and distribute the load.”
Crews will excavate the stream bed using a standard excavator and other small equipment. The challenge is to pour the concrete in place and then go back and put them stream material in the culvert itself, Kohn said. The smaller Bobcat equipment will be moving material around, then they’ll cast the top of the culvert and put it in place, he said.
“When all is said and done, you shouldn’t see anything but brand new pavement and the shoulder slightly wider to accommodate the guardrail. When we are done the diversion goes away, and after being blocked for more than 50 years, the natural tidal flow of Fraser Creek will be restored.”
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