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County weighs state, federal cooperation on flood mitigation

Nov 28, 2012 - By Eric Blom, Staff Writer

The Fremont County Commission is considering joining the Wyoming Department of Transportation on a flood mitigation project on the Wind River.

In July 2011, a flood overran the riverbank west of Riverton near mile 104 on Highway 26. Water flooded nearby properties and the Marathon Oil field and undercut the highway.

The flood lowered the riverbank 8 to 12 inches, and road repairs cost $432,000, WyDOT District 5 Engineer Shelby Carlson said during the commission meeting Nov. 20.

The flood mitigation project would make the river flood less frequently and prevent it from cutting a new channel across Highway 26, private property and the Marathon Oil field, Carlson said.

She said WyDOT would pay 25 percent of the project and do the work. She is applying for money from the Federal Emergency Management Agency to pay the balance of the cost.

Fremont County would own the project, she said, and she asked if the county would agree to maintain it. The FEMA application requires a guarantee that an agency will maintain the project, Carlson said.

Three-part plan

She explained the flood mitigation project would have three components. The first is to raise the bank to its height before the flood.

"It's a foot lower," Carlson said. "It's going to flood more."

With banks back to their 2011 height, the river would flood less frequently but still would run over if as much water came down as was seen in 2011.

Carlson said FEMA would only fund the project if crews did not raise the banks higher than they were originally. The agency would consider higher banks a levee, and it does not pay for levees, she said.

Besides flooding, though, the river is slowly carving a new channel pushing the river east. That channel would eventually run through the areas it flooded, over the highway and beyond into more private properties.

"It would cut down through where the flood waters crossed over top the road," she said.

She said that in another flood the river could "cut and run," suddenly carving the channel it has been moving toward.

Bank stabilization

The other parts of the project would keep the river on its current course, especially during a flood, Carlson said.

One step is to cover the river's east bank with fabric and heavy stones, she said. Such armor stops the bank's erosion and the river's eastward meander.

The final part is to install long piles of rocks called "j-hooks." Carlson said these piles would angle away and downstream from one bank to divert water from that side, further preventing erosion.

At the meeting, commission chairman Doug Thompson asked what maintenance would be and much it would cost.

"I can't see much maintenance of it, maybe clearing some debris," Carlson said.

She did not have exact costs.

"The only thing I'm sure of is periodic inspection," said Fremont County Emergency Management Coordinator Kathi Metzler. "Someone goes out there and checks for certain things."

"We have put in a lot of these in the last couple years," Carlson said later. "Maintenance cost is very little."

Thompson said he was concerned that the project would not prevent flooding if the water was as high as in 2011 because the project did not raise the banks.

"If you look at raising this...you cut off flood plain, reduce flood storage," Carlson said. "The water would go downstream. ... It's going to do something more drastic downstream. You kind of need that flood plain."

Weighing options

Fremont County Transportation Department superintendent Dave Pendleton asked what would happen if the county denied the partnership.

FEMA would deny the application, and WyDOT could not fund the project on its own, Carlson said.

"We would take a 'sit back and wait' approach," she said. "By the time it cuts back to the highway, that structure may have served its purpose"

Riverton District Crew Chief Rocky McWilliams said, "If nothing is done it will take its own channel again, it will take the highway out and landowners."

The commission decided to take the issue under advisement while it sought more information.

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