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Fish Passage Improvement Slated for the Dalles Dam by CBB Staff Columbia Basin Bulletin - September 12, 2003

The U.S. Army Corps of Engineers has awarded a $4.2 million contract to improve juvenile fish passage at The Dalles Lock and Dam on the Columbia River.

Robert B. Goebel, general Contractor from Spokane, Wash., was awarded the contract to construct two walls extending from the dam's spillway into the Columbia River, and repair some erosion damage at the base of the northern-most spill bay.

Construction mobilization efforts will begin immediately, however physical work in the water will take place after Nov. 1 to avoid potential impacts on migrating fish. Work is scheduled to be completed by March 2004, the beginning of the spring salmon migration.

The primary wall -- to be built between spill bays six and seven -- will be 193-feet long, 43-feet high and 10-feet wide. An existing 8-foot-wide secondary wall, located at the north end of the spillway, also will be lengthened 47 feet as part of this work.

Unlike other Columbia and Snake river dams, The Dalles Dam does not have a juvenile bypass system and the primary route for juvenile salmon passage is through the spillway. Research has revealed that juveniles are injured at higher rates going through the spillway at The Dalles than at other spillways in the system. Research found injury rates as high as 14 percent for fish passing The Dalles Dam spillway while similar research at other Columbia and Snake river dam spillways show injury rates typically to be less than 5 percent.

Fishery research conducted at The Dalles Dam and at the Corps' Hydraulic Research Laboratory in Vicksburg, Miss., between 2001 and 2003 identified lateral flows at the spillway base that are potentially harmful to juvenile fish as they pass the dam during their journey to the sea. This condition keeps juvenile fish in the turbulent water at the base of the spillway longer, thus increasing the chance for injuries from contact with concrete structures and predation.

The walls are designed to improve the flows in the northern-most six of the 23 bays to more quickly and safely move the juvenile fish into the main river channel downstream. In the future, the Corps will confine spill to these six bays until river flows exceed their capacity, at which time it will open additional bays as necessary.

Additional research is under way to identify other promising improvements for fish passage at The Dalles Dam.