Mill Creek Fish Passage treatment

Mill Creek fish passage treatment between Clinton and Division shows the various techniques used by the Tri-State Steelheaders to support salmon runs through the concrete channel through Walla Walla, Set. 8, 2021. On the right, roughness patches help create friction and slow the flow of water through the creek, while lateral concrete baffles on the left help control sediment.

The Tri-State Steelheaders are nearing the halfway mark on their work started more than 10 years ago to encourage salmon runs through Mill Creek.

Now, the salmon restoration group is eyeing three more stretches of the concrete channel that controls the creek as it moves through Walla Walla: between Roosevelt Street and Division Avenue, between Sixth and Third avenues, and an underground section between Third Avenue and Colville Street.

They are only the latest phases in a decade-long effort to remediate the artificial concrete channel that Mill Creek flows through to make the waterway passable by summer steelhead, bull trout and reintroduced spring Chinook.

Those salmonid species once spawned freely in Mill Creek and its upstream tributaries but have since been greatly diminished by dams and other man-made structures, said Brian Burns, executive director of the Tri-State Steelheaders.

The 7-mile-long channel, including 2 miles of concrete, was originally built in the 1930s and ‘40s and was designed largely with flood control in mind.

But the way it was originally shaped is not favorable to fish passage, with water moving too fast for adult fish to easily navigate upstream or for juvenile fish to survive the trip downstream, Burns said.

Members of Tri-State Steelheaders have worked for years to remediate this by replacing portions of concrete with “roughness panels” throughout the concrete channel. These have studded projections that create friction and slow the creek.

The group is also planning to do work on the channel’s baffles, which are a configuration that is used to control sediment build up. As the water flows around each baffle, it accelerates and becomes shallower in those sections, making it more difficult for juvenile fish to navigate up and down the waterway to find cooler pools or evade predators.

On Monday, Jan. 11, the Tri-State Steelheaders received landowner agreements from Walla Walla County, which is responsible for the concrete channel itself, for the three upcoming sections of the channel. Those landowner agreements allow the group to apply for grants from the Fish Barrier Removal Board, Burns said.

Bids have already gone out for construction of the first section between Roosevelt and Division. The Tri-State Steelheaders originally received grant funding for the project in 2019, but rising construction costs have prompted the group to prepare to potentially request additional funds, Burns said.

The other two sections could prove trickier than earlier areas of the channel, he added.

The stretch between Sixth and Third avenues runs underneath the Fifth Avenue bridge, which could have complicated attempts to remediate the concrete in that section. Because there is a support pier for the bridge in the channel, new baffles and roughness panels couldn’t be added while still leaving sufficient room for the county’s maintenance vehicles to navigate that space in the future.

But the city of Walla Walla has independently moved forward with plans to remove that bridge, Burns said, providing Tri-State Steelheaders an opportunity to apply fish passage treatment measures to that area.

The final section runs underground between Third Avenue and Colville Street. Tri-State Steelheaders is currently only applying for grant funding to pay for design of that section, Burns said, because that section is differently constructed than the rest of the channel.

“The engineering needs to be adapted to fit the conditions underground,” Burns said. “Looking ahead to construction, we also want a work safety plan in place for people working down there, and there are also structural concerns that we don’t have elsewhere.”

Construction activity would vibrate the channel, and the roof of the underground section needs to be inspected to ensure that construction will not pose a risk, he continued.

The decades-long project to remediate the entire concrete channel is about halfway done, and it’s hard to say what impact it has had while still incomplete, Burns said. The group has focused its funds toward construction, not fish monitoring, he said, and there are a number of sizable gaps in passage treatment that could foil fish attempting to make their way through Mill Creek.

However, there has been some anecdotal evidence that fish are beginning to be seen upstream of the concrete channel, Burns said.

Emry Dinman can be reached at emrydinman@wwub.com or 425-941-5829.

Reporter covering agriculture, Walla Walla city and county government, and other topics.

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