Work aims to make Mill Creek a fishier neighborhood

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Often when we think of fish habitat, we think of plunging streams in rural or remote locations. Seldom do we think of concrete.

But the Tri-State Steelheaders and our partners are now embarking on a series of projects aimed at improving fish passage in the concrete-dominated portions of Mill Creek.

The U.S. Army Corps of Engineers completed flood control measures on Mill Creek in the 1940s. The Corps still owns and operates the portion above the Division Dam at the Mill Creek Project Office.

The roughly six miles of channel downstream of the Corps property is maintained and operated by Walla Walla County Public Works. It is this section where our work is focused.

Above the flood control project, upper Mill Creek provides spawning and rearing habitat for reintroduced spring chinook and for summer steelhead and bull trout that are listed as threatened under the Endangered Species Act. Other aquatic species of state concern and cultural significance are also found in Mill Creek.

Though upper Mill Creek is considered to have good to excellent habitat (including the protected watershed), fish managers feel Mill Creek should be producing more fish. It has been assumed for years that poor passage in the flood control channel was a major factor.

The Mill Creek Work Group has discussed these and other issues for years. The group includes representatives from federal, state, local, tribal and non-governmental entities.

The group initiated a formal fish passage assessment of the channel, completed in 2009, that identified the location of fish passage barriers and described the nature of the barriers. While some expected to find a few barriers at specific points, the assessment found a more complex problem. Barriers depend on both the flow in the channel and the location in the channel. Any given section of channel is a barrier at some flows, but not at all flows.

Last year we began on-the-ground work to improve Mill Creek passage with three projects. At Tausick Way, four of the energy-dissipating weirs were notched to provide low-flow passage. High-flow passage is not a problem in this section of Mill Creek.

At Ninth Avenue and at Roosevelt Street, each end of the concrete channel was modified for passage. Baffles in the center trench were reconfigured to eliminate low flow problems related to depth. Roughened surfaces were added to simulate a natural bottomed channel, providing a slower velocity area during higher flows. Resting pools were also added. At all locations, work primarily involved cutting and removing concrete, and replacing with new pre-cast and poured concrete.

These projects were all designed with the caveat that they would maintain or increase the flood control capacity of the channel. These projects were also reviewed and approved by the Corps of Engineers for structural integrity and flood capacity.

After seeing the successful completion of these projects, the Work Group has shifted focus to the concrete channel between Roosevelt Street and Ninth Avenue. At a little over two miles, improving passage in this section will take several projects over several years.

Looking ahead, funding is in place and we are on schedule to construct passage improvements between Spokane and Colville Streets in 2013. We are also applying for additional funds to extend the passage improvements at Ninth Avenue upstream another 500 feet.

Including the assessment, our completed work totals more than $1.3 million to date. Our funding comes primarily through the Salmon Recovery Funding Board, Confederated Tribes of the Umatilla Indian Reservation and Bonneville Power Administration. All of the work has been provided at no local cost.

All of this work is being conducted with the vision of recovering our ESA-listed stocks. Passage in Mill Creek is necessary to fulfill de-listing criteria and to produce more fish.

Recovered stocks and a healthy spring chinook fishery would lead to increased opportunities for recreational fishing and the economic benefits to the community that go along with healthy fisheries.

Brian Burns is project manager for Tri-State Steelheaders.

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