Flood mitigation

Flood mitigation efforts around Colorado Gulch have warped the Big Wood River’s flow through the area.

The Blaine County commissioners approved a stream alteration permit application from the Wood River Land Trust on Tuesday, authorizing long-proposed plans to revert a stretch of the Big Wood River within the popular Colorado Gulch Preserve back to its natural state.

The project—first floated  by the Land Trust in 2018 after the Colorado Gulch bridge was wiped out by floods the year before—will  involve recreating a 400-yard historic side channel on the east side of the river, excavating over 100 cubic yards of basalt riprap and reconnecting the river to its natural floodplain habitat.

Work should get underway in mid-November, according to Wood River Land Trust Restoration Specialist Ryan Santo.

“We envision restoring this part of the Big Wood by removing confining structures that artificially constrict the river,” Santo said. “If we can connect the [river] back to its natural floodplain, we can slow it down and allow water to filter down to the aquifer.”

Today, the historic eastern side channel only fills during high-water periods, Santo said, leaving ideal trout spawning habitat dry most of the year. Bank-armoring efforts in response to major flooding events over the years have further restricted floodplain habitat, he told the Express.

 “The county has used riprap as a bank-hardening tool since the early 1980s,” Santo said. “The thought is that they don’t want that bank to move or the river to encroach into it.”

The Land Trust also has plans to address long-term effects of erosion this fall, using bank stabilization devices such as apex jam (or log-bundle) structures and brush trenches.

“Healthy riparian habitat doesn’t only serve fish. Seventy percent of birds at some point of their life history spend time in floodplain habitat,” Santo said. “And river corridors are often used as migration routes for elk, deer and moose.”

Bridge options under review

For decades, motorists and pedestrians had used the former Colorado Gulch bridge—a popular access point for hikers, bikers and hunters—to access Bureau of Land Management land to the west. The original 80-foot steel bridge failed in 2017 after floodwater was funneled toward the abutments. Portions of concrete footings are all that remain of the structure today.

“The bank-hardening efforts didn’t allow the river to come east at all, which led to the demise of the bridge,” Santo said.

A replacement pedestrian bridge will likely be installed after river restoration work wraps up this winter. The Land Trust is currently evaluating three different nonmotorized bridge options, including a 500-foot suspension bridge from the preserve’s parking area to the original bridge site,  a shorter 350-foot bridge across the river with an access path, and a 120-foot suspension bridge accompanied by a series of shorter bridges over side channels.

Of the three options, the 500-foot bridge is the Land Trust’s top pick, as it would enable residents to access Colorado Gulch during high flows. The only drawback is cost, Santo said. That type of suspension bridge would likely cost between $1 million and $1.2 million.

“The county does have around $250,000 from the [Federal Emergency Management Agency], which leaves about one million,” Santo said. “I’m unsure how we would fundraise for the new bridge, but I would imagine it involves several public meetings onsite, possibly public tours and a fundraising event.”

Santo said because Blaine County maintains a right-of-way through the preserve along the riverbank, including the approach to the bridge site, the county would own the future bridge and provide input on its design in coming meetings.

On Tuesday, Jacob Greenberg, chairman of the county commissioners, said he was concerned that the 500-foot bridge option would rack up considerable maintenance costs every year and the multiple-bridge option could “mess up” the Land Trust’s proposed restoration work.

Commissioner Dick Fosbury disagreed.

“This project that the [Land Trust] has designed is not going to interfere with a future bridge,” Fosbury said.

The Land Trust purchased the 150-acre Colorado Gulch Preserve, mostly cottonwood forest, in 2016 from the Stevens Family Ranch, effectively lengthening the southern reach of the Hailey Greenway by about a mile. Since then, the Land Trust has kept the cottonwood forest preserve open to the public during the daytime.

Email the writer: ejones@mtexpress.com

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