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New 'Fish Slide' for Lower
Monumental Dam behind Schedule

by Staff
Columbia Basin Bulletin, November 3, 2006

Construction of the latest "removable spillway weir" to be added to the Columbia/Snake river hydrosystem fish passage toolbox is behind schedule by an estimated 32 days, threatening its installation in time for the 2007 spring juvenile outmigration.

The window for completion and installation of the RSW at the lower Snake River's Lower Monumental Dam has shrunk as a result of the lagging fabrication of what will be a nearly 2 million-pound structure. The goal was to have the RSW towed upriver from the Portland area to Lower Monumental, some 280 miles, by Feb. 20.

Achieving that goal is now unlikely, NOAA Fisheries' Bill Hevlin told members of the Implementation Team Thursday. Installation of the RSW is on NOAA's list of things to do in its 2004 biological opinion on the Federal Columbia River Power System. It is among the actions in the BiOp intended to improve fish passage survival. The multi-agency IT helps coordinate timely implementation of the BiOp.

A new goal is for delivery of the RSW by March 9. That is the day before the navigation locks at the eight FCRPS dams are shut down for a two-week period for annual maintenance. During that March 10-24 period that RSW could not be towed upstream.

That maintenance period, done at a time of the least barge and recreational vessel traffic, was moved back by one week to allow extra RSW construction time.

"They're not making any promises," said Kevin Crum, RSW project manager for the Corps of Engineers Walla Walla District, said of the contractors. "But we're hoping that in four months we can make up two weeks" of lost time on the construction schedule.

The subcontractor charged with fabricating the structure is working two 10-hour shifts on the project, Crum said.

Once it arrives at the dam, it is expected to take about a month to install the RSW. The target is to have the fish passage device operational in the dam's spill bay 8 by April 13.

By mid-April the juvenile salmon outmigration from the Snake is beginning to build. Likewise flows begin to grow with the advent of the spring runoff.

The construction will require that the adjacent turbine unit and spill bays to be shut off to provide a safe in-water work environment, Crum said. That would limit the passage options for both water and fish, something that would likely not be acceptable. The bulk of the river flow, and fish, go through units and spillbays on the north side. Fewer normally pass through the 5 spill bays that would remain operational during construction on the south side.

"We would have to decide whether it's worth the risk of starting the installation" later in March, Crum said.

'If they can't make this by March 9 we will not have an RSW at LoMo" in 2007, Jim Ruff of the Northwest Power and Conservation Council staff noted at the IT meeting.

Hevlin said it was important for NOAA, and the region's salmon restoration efforts, to get the new RSW in place.

Biological testing at Lower Granite has shown that its RSW is five times more efficient at attracting juvenile salmon and steelhead than traditional spill. Testing at Lower Granite and Ice Harbor noted an average of 98-percent survival for fish passing the dams via the weirs, according to the Corps.

Spilling less means more power can be generated and sold. Spill is considered by most to be the safest route of passage for the fish. Lower Granite's was the first RSW installed in the system, in 2001. An RSW installed at the lower Snake's Ice Harbor Dam last winter was operation for the 2006 migration. It too has shown promising biological results, Hevlin said.

He said that the Lower Monumental RSW could provide the best results of the three, since most of the approaching fish already zero in on the north-end spillbays.

The Corps of Engineers awarded the $15 million RSW contract to an Oregon City, Ore., company in April. Advanced American Construction Inc. was selected from among two companies submitting proposals. The RSW is being fabricated in Portland at the Cascade General Shipyard by Oregon Iron Works of Clackamas.

Lower Monumental RSW is a floating, surface bypass structure that will be about 120-feet high, 80-feet wide and 70-feet deep in the installed position. The main element of the RSW design is the sloped weir "fish slide," which passes surface water for juvenile fish traveling from the forebay (upstream side) of the dam to the tailrace (downstream side) of the dam, according to the Corps.

The design of a spillway weir is different from existing spillways which open their gates 50 feet below the water surface at the face of the dam and pass juvenile fish under high pressure and high velocities. The RSW passes juvenile salmon and steelhead over a raised spillway crest where juvenile salmon and steelhead pass near the water's surface under lower accelerations and lower pressures.

The RSW is designed to be "removable" by controlled descent to the bottom of the dam forebay. The structure is hinged to allow rotation to the river bottom for removal. This capability permits returning the spillway to original flow capacity during major flood events.

Find more information about the spillway weir and other programs to benefit anadromous fish in the Columbia River Basin at the Corps' " Fish Programs" links on the Walla Walla District's homepage

New 'Fish Slide' for Lower Monumental Dam behind Schedule
Columbia Basin Bulletin, November 3, 2006

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