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River Managers Agree to Begin Spill on Lower Columbia Dams

by Mike O'Bryant
Columbia Basin Bulletin - April 11, 2003

With a rising water supply forecast and juvenile fish already showing up at dams, the decision this week by the Technical Management Team to begin spill at four dams in the Lower Columbia River was made without challenge.

Federal, state and tribal fisheries managers proposed to federal operating agencies to begin spill at McNary, John Day, The Dalles and Bonneville dams and to start the spill Monday, April 14.

In its final April water supply forecast, released April 8, the Northwest River Forecast Center predicted an available water supply January through July at The Dalles Dam of 85.3 million acre feet of water or about 79 percent of normal. That is an increase over the April early bird forecast, released March 27, which was 82.3 maf.

"Our principle concern right now is with the fish coming out of the John Day and Umatilla rivers that already are in the lower stretch of the Columbia," said Dave Wills, U.S. Fish and Wildlife Service.

He said that because the fish were already present in much of the lower river, that fisheries managers were recommending beginning spill at the four dams all at once, rather than sequence spill at the dams every two days as TMT did at lower Snake River dams just last week. The decision last week to spill at the Snake River dams was much more contentious because the water supply forecast and corresponding expected seasonal flow were just under the NOAA Fisheries biological opinion criteria that would automatically kick-in spill.

The Lower Granite Dam final April water supply forecast also rose to 17.1 maf, April through July, or 79 percent of normal.

Juvenile passage numbers have been on the rise at the John Day Dam for over week, according to the system operations request (SOR). About 13 million hatchery juveniles had been released by April 3 and another 22 million are expected in the next two weeks.

"While the second half of April is not normally characterized as a significant passage period for spring migrating juveniles as a whole, it does represent a period of time when significant proportions of specific stocks are migrating," the SOR reads. It specifically identified stocks from the John Day, Umatilla and Yakima rivers. "If spill is not initiated early enough during the migration season there is a higher likelihood that these stocks will pass under no spill conditions."

A 12-hour spill at McNary Dam begins at 6 p.m. on April 14. When spilling, 50,000 cubic feet per second of water flow will flow through the powerhouse and the remaining water in the river will be spilled up to the total dissolved gas cap of 120 percent.

There will be a one day spill-test April 10 at the John Day Dam from 7 a.m. to 5 p.m., spilling 30 percent of the river for a hydraulic modeling test. Nighttime spill of 60 percent of the river will begin again at 6 p.m. April 14 up to 300 kcfs. Above 300 kcfs, the limit on spill would be the 120 percent spill cap.

A 24-hour 40 percent spill will begin at The Dalles Dam at 6 p.m. April 14. However, a three-week spill test at the dam will cause spill to fluctuate some hours, said Scott Bettin of the Bonneville Power Administration.

Spill at Bonneville Dam will begin at 5 a.m. April 14 to accommodate an adult fallback study. Spill is limited at the dam to 120 percent gas cap during nighttime hours and 75 kcfs or the gas cap during daytime hours.

Related Sites:
Technical Management Team:
Northwest River Forecast Center:

Mike O'Bryant
River Managers Agree to Begin Spill on Lower Columbia Dams
Columbia Basin Bulletin, April 11, 2003

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