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ESA-Listed Chum Salmon Arrive Early Below Bonneville Dam; Flow Operations Begin To Protect Spawning
Posted on Friday, November 02, 2018 (PST)

Although the count varies by day, as many as 137 chum salmon were counted on one day in late October downstream of Bonneville Dam where they are expected to build redds (nests) and spawn during November and into December.

 

The early arrival of chum, listed as threatened under the federal Endangered Species Act, led to the request from fisheries managers and the decision this week by the interagency Technical Management Team to begin the annual chum operations that will continue through the next five months, transitioning to chum incubation flows in late December.

 

Chum operations at the dam began today, Friday, Nov. 2, at 6 am. The operations will maintain the dam’s tailwater elevation at 11.5 feet so that the fish can move into spawning areas near Hamilton Creek and Ives Island.

 

The chum were counted in late October, but tailwater levels at the time were under 10 feet and much of the spawning area that will be available to them as of today was unusable due to shallow water. Some 60 chum were counted by Washington Department of Fish and Wildlife biologists Oct. 22 and the biologists saw 137 chum Oct. 25. Three chum have passed over Bonneville Dam.

 

Annual chum operations ensure that enough water will flow over chum redds to protect the redds and fertilized eggs until they emerge in spring. Initial spawning operations seek flows high enough to protect chum as they build their redds, but not so high that chum would have been encouraged to spawn in areas that could be dewatered when flows drop.

 

Last year, TMT began chum operations Nov. 7. Due to the early arrival of the chum, operations this year are beginning one week early.

 

TMT met for an unscheduled conference call Monday, Oct. 29, to consider an early start to the chum operations. At that time, flows at Bonneville were just 98,000 cubic feet per second, but rain over the next 10 days, according to Doug Baus of the U.S. Army Corps of Engineers, should bring flows up to about 128 kcfs.

 

The Northwest River Forecast Center had forecasted Bonneville Dam flows today to hit about 123 kcfs and predicts flows will rise to about 133 kcfs by Nov. 5 (see https://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?id=BONO3), but that’s without initiating the chum operations.

 

With local rain, flows by Tuesday had risen to about 103 kcfs, with a tailwater elevation of 9.4 feet. Baus said precipitation over the 10-day period will be 110 to 175 percent of normal in southwest Washington and Northwest Oregon, with three-quarters to 1-1/4 inches expected into this weekend alone.

 

More than two weeks ago when TMT last met to discuss chum operations, the outlook was much different as the river operating group was looking at a continued dry fall (see CBB, October 12, 2018, “Providing Water Cover For ESA-Listed Chum Salmon Redds Below Bonneville Dam Could Be Tough This Year,” http://www.cbbulletin.com/441644.aspx). Flows were at 91.3 kcfs with a tailwater elevation of 8.7 feet as of Oct. 8. TMT wondered if a significant amount of flow augmentation would be needed from the Grand Coulee Dam’s Lake Roosevelt.

 

“Two things have changed” over the last two weeks, Baus said. “The weather forecast and the arrival of the chum,” explaining why TMT was meeting to consider an early start to chum operations.

 

To raise the tailwater level up to 11.5 feet may take some additional water from Grand Coulee, but with the rain this week, it is likely that less than one foot of the reservoir level will be needed to augment chum flows, according to Scott Bettin of the Bonneville Power Administration.

 

Chum operations began at 6 am this morning. The Corps will maintain a tailwater elevation of 11.5 to 13 feet. Actual flow at the dam at 6 am this morning was 146.5 kcfs and the tailwater elevation was at 12.1 feet.

 

As flows rise, TMT has adopted tiered guidance for the operation:

 

If flows rise and if necessary, the tailwater can go to 16.5 feet during the night (5 pm to 6 am), concentrating the highest elevation around midnight.

 

With even higher flows, the tailwater can rise to 18.5 feet during the night.

 

“Then, if increasing river flow precludes the ability to manage tailwater within the steps above, operate to provide a tailwater in the range of 13 to 16.5 feet during the day (6 am to 5 pm) and up to the maximum within project 24-hour ramp rate limits during the night,” the coordinated chum operations for 2017/18 says (http://pweb.crohms.org/tmt/agendas/2018/1003_Agenda.html).

 

Once started, TMT will continue flows and tailwater elevation to protect the chum redds into mid- to late December and then transition to similar flows to protect the redds through incubation.

 

Also see:

 

--CBB, January 19, 2018, “Agencies Identify Spawning Areas For Chum, Confirm Safe Water Levels Over Redds,” http://www.cbbulletin.com/440103.aspx

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