A $32 million project is under way at the Mid-Columbia’s Chief Joseph Dam aimed at reducing total dissolved gas that can harm aquatic organisms, including protected salmon and steelhead, in the river below.

Work began recently to install spillway deflectors at the bottom of each of the dam’s 19 spillways. A crew of about 20 will be working five days a week for the next 2 ½ years, with occasional Saturday shifts, to complete the work.

When it is finished, the long-envisioned improvements will allow the Corps of Engineers to spill more water through the bays while reducing an unhealthy side effect of the practice, the creation of TDG.

The project includes a so-called power swap with the Bureau of Reclamation’s Grand Coulee Dam that should also serve to reduce gas concentrations in the river. Once the flow deflectors are operational, Grand Coulee would begin pushing more water through its generators during high flow periods, and spilling less. Grand Coulee does not have spill deflectors.

In essence Chief Joe, the next dam downriver, would spill the water Grand Coulee would have spilled, and Grand Coulee would generate the power that Chief Joe would have generated with the spilled water. Grand Coulee has a much higher powerhouse capacity than Chief Joseph.

“That’s very significant,” NOAA Fisheries’ Mark Schneider said of the potential gas reductions at both Chief Joe and Grand Coulee. The idea was first posed in 1997 and made formal in NOAA’s 2000 biological opinion on Federal Columbia River Power System operations. An updated BiOp issued in 2004 also called for the flow deflector installation.

The Corps, which developed the project, has estimated that the total dissolved gas reduction could exceed 15 percent under extremely high flows. Prototype testing of the deflectors after the installation contract is complete will provide data to check the accuracy of the TDG model, according to the Corps Dick Devlin.

The goal of the project is to reduce TDG concentrations downstream of Chief Joseph to 120 percent, the maximum allowed under frequent flows up to the seven-day, 10-year flood event.

Unlike other dams, Chief Joseph and Grand Coulee only employ “involuntary” spill forced by high spring flows, low power demand or maintenance outages. NOAA BiOps call for spill at most of the other dams in the federal Columbia-Snake system to facilitate salmon passage. Salmon passage to the upper Columbia has been blocked since the completion of Grand Coulee in 1941.

Fish benefiting from the gas reduction would benefit include the Upper Columbia spring chinook salmon and Upper Columbia steelhead, listed as endangered and threatened, respectively, under the Endangered Species Act. Those stocks swim the mainstem Columbia on their way to tributaries such as the Methow, Entiat and Wenatchee rivers.

The Corps estimates that the gas reduction will benefit stocks as far as Priest Rapids Dam, nearly 150 miles and four dams downstream.

TDG supersaturation generated by spill increases the potential for gas bubble trauma in fish exposed for an extended period. The gas comes out of solution within the fish, forming bubbles in the body tissue. Such trauma can be lethal at high saturation levels or result in chronic impairment at lower levels.

The flow deflectors, shaped similarly to ski jumps, will deflect the spillway water jet along the surface of the tailwater. That will reduce “plunging” of the jet, which entrains gas in the water below.

Upon completion of the installation, a final test will be carried out to verify the deflector performance. That test will employ from 180,000 to 220,000 cubic feet of water.

The project has been supported by NOAA, the Bonneville Power Administration, the Environmental Protection Agency, Washington Department of Ecology, Confederated Tribes of the Colville Reservation, and other resource agencies throughout the Columbia basin. The project will be funded through the Corps’ Columbia River Fish Mitigation Program. Funds for the program are appropriated by Congress. BPA, which markets power generated at the federal dams, reimburses the U.S. Treasury for the CRFMP costs.

Traylor Brothers Inc., was awarded the spillway deflector installation construction contract by the Corps on Aug. 19, 2005. Work activities will be centered on the face of the spillway near the dewatering caisson — the cofferdam that allows workers to construct spillway deflectors in the dry.

Meanwhile, the Corps is trying to reduce impacts to the public’s access to the river. Work on the right bank has been limited to a fenced area, and new access stairs have been installed.

Changes in river and reservoir management may be required to ensure worker’s safety below the spillway, according to the Corps. Spill may be necessary during the during the construction contract, but may be confined to a group of gates away from the work area, rather than across the whole spillway.

The Corps expects that any small changes in the river downstream of Chief Joseph Dam and the Rufus Woods Lake level will have minimal impacts to fish, wildlife, and water quality, and they should not affect recreation, fishing or irrigation.

Tribal anglers will experience some changes in fishing access over the period of the construction. The Corps is planning to meet with tribal anglers Tuesday, June 27, from 4 to 5 p.m. at the Long House in Nespelem, Wash., to discuss the construction schedule and potential construction impacts to bank access and traffic. The Corps is coordinating this meeting with the Confederated Tribes of the Colville Fish and Wildlife Department, which will provide further information. The tribes’ Fish and Wildlife office will answer questions regarding the meeting. This office can be contacted at (509) 634-2110.

More information about Chief Joseph Dam can be found at http://www.nws.usace.army.mil/PublicMenu/Menu.cfm?sitename=cjdam&pagename=mainpage