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River Managers Stick to Nez Perce/Idaho Dworshak Plan

by Mike O'Bryant
Columbia Basin Bulletin - August 8, 2003

With cooler weather forecasted, fisheries and operations managers of the Technical Management Team this week agreed to again lessen outflows of cool water from Dworshak Dam to about 9,000 cubic feet per second beginning Monday evening.

The operation is on track with a Nez Perce Tribe and Idaho Department of Fish and Game system operations request to save 200,000-acre feet of the dam's cooler water for juvenile and adult fish migrating in early September.

This is the third reduction of the cold water discharge from the dam in as many weeks. NOAA Fisheries' 2000 hydrosystem biological opinion calls for releasing cold water from the dam on the North Fork of the Clearwater River through August to help lower river temperatures downstream at Lower Granite Dam on the Snake River. Under the BiOp all the water available from the reservoir would be used up by Aug. 31, on that date targeting a reservoir elevation of 1,520 feet.

However, a counter operations suggested by the Idaho Department of Fish and Game and the Nez Perce Tribe would instead aim for an Aug. 31 reservoir elevation of 1,535 feet, saving some of the augmentation water for juvenile and adult migrations during the first two weeks of September. TMT has agreed to attempt to meet this operation as long as the tailwater temperature at Lower Granite Dam remains below 68 degrees.

Even with the recent spate of over-100 degree Fahrenheit weather in the Snake River Basin, according to Paul Wagner of NOAA Fisheries, the tailwater temperature at Lower Granite Dam, the most upstream dam of the four lower Snake River dams, has hovered at an average 65.5 degrees, largely due to the 45 degree water released from Dworshak Dam.

"The weather is in our favor and is pumping cooler air across the region," said Kyle Martin of the Columbia River Inter-Tribal Fish Commission. "Instead of the 100-degree weather, it's now down into the 80s and low 90s for the next 10 days, and we could see shots of precipitation through the week. I don't see any return of major heating this year like we saw in July."

Wagner said that the number of juvenile chinook salmon showing up at the dam had increased slightly this week after falling off in previous weeks. 839 juveniles had passed July 31, 1,100 Aug. 1, and this week passage is about 4,500 fish per day. Still, wild chinook subyearling pit tag data is showing that, as of Aug. 4, about 95 percent of those juveniles have passed Lower Granite Dam, 93 percent at Little Goose Dam, 90 percent at Lower Monumental Dam, 87 percent at Ice Harbor Dam and 85 percent at McNary Dam (of those fish that remain in the river).

The U.S. Army Corps of Engineers dropped outflows from 14 kcfs to 12 kcfs the last week of July. Both flow levels require some level of spill. Monday, Aug. 4, it dropped flows again from 12 kcfs to full powerhouse discharge, which is 9.8-9.9 kcfs, according to the Corps' Cindy Henriksen. And, it is likely to drop outflows to about 9 kcfs Monday evening, Aug. 11, contingent on continued favorable tailwater temperatures at Lower Granite Dam and on agreement by TMT fisheries managers. Those managers will review conditions today and, if temperatures have risen, could notify TMT Monday.

That's on track with the Nez Perce Tribe and IDFG SOR, she said, but with a slight variation, which will show up the last week of August when outflows will have to drop lower than the tribes/Idaho operation to about 7 kcfs so that the reservoir elevation level lands on 1,535 feet at the end of August. Outflows will rise to about 8 kcfs, providing more water for early-September migrants.

"The 1,535 feet (elevation at the end of August) is important to us because the difference between that and 1,520 feet is the 200 kaf we're asking for in September," Martin said. The elevation Wednesday morning of this week was 1,561 feet, down 39 feet from full.

Related Sites:
Technical Management Team:

Mike O'Bryant
River Managers Stick to Nez Perce/Idaho Dworshak Plan
Columbia Basin Bulletin, August 8, 2003

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