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Flows Managed To Aid ESA-Listed Chum Salmon Continuing To Arrive Below Bonneville Dam
Posted on Friday, December 14, 2018 (PST)

With more than 300 threatened chum salmon still hanging out in spawning areas downstream of Bonneville Dam, the interagency Technical Management Team this week put off a decision on whether to transition from the chum spawning operations that began early last month to incubation flows.

 

The most recent surveys by Washington Department of Fish and Wildlife biologists of Bonneville spawning areas found 322 of the fish near Ives/Pierce island complex on Dec. 4, and 61 chum at Horsetail, 5 at Marker 85, 120 at Multnomah Falls and 5 at St. Cloud, all on Nov. 28. Some 126 chum have passed over Bonneville Dam as of Dec. 11.

 

(See maps of chum spawning areas at http://pweb.crohms.org/tmt/agendas/2018/0117_Ives_Island_Spawning_Areas_2017.pdf)

 

The chum, listed as threatened under the federal Endangered Species Act, arrived early this year and chum operations to protect the fish and their redds (nests) began Nov. 2, about a week earlier than normal. Operations for the chum go on for about five months, but generally transitions in late-December from spawning to chum incubation flows.

 

“Typically this week of December we think about ending (spawning) chum flows,” said Tony Norris of the Bonneville Power Administration during the TMT meeting Wednesday, Dec. 12. “But we’re still seeing about 300 live chum and some ‘green’ fish in the area.”

 

Still, TMT could decide next week as early as Tuesday whether it’s time to transition to incubation flows, which are designed to protect the redds through incubation. Last year that operation called for an 11.8 foot minimum tailwater elevation at the dam at all hours for as long as up to April 10, 2018, or through incubation.

 

Spawning flows will end automatically Dec. 31 if TMT doesn’t purposely make the transition earlier, said BPA’s Scott Bettin.

 

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.

 

Spawning operations maintain the dam’s tailwater elevation at a minimum 11.3 feet so that the fish can move into spawning areas near Hamilton Creek and Ives Island.

 

However, a special operation was adopted by the U.S. Army Corps of Engineers, with the approval of WDFW, Dec. 7 when down power at the Columbia Generation Station required the Corps to move an additional amount of water through the system, according to a memo from the Corps’ Doug Baus.

 

“Due to generally dry conditions we are making a small adjustment to the chum operation to minimize the risk of chum spawning at higher elevations while this water moves through the system,” the memo says.

 

To do that, the Corps narrowed the daytime tailwater elevation from 11.3 to 13.0 feet down to 11.3 to 12.0 feet in order to keep the daytime tailwater below elevation 12.0 feet and move any additional water at night.

 

The situation eased by Tuesday, Dec. 11, and chum operations returned to a 24-hour tailwater elevation of 11.3 to 13 feet, Baus said.

 

He said that precipitation in the basin has generally been below normal: 81 percent of normal in the Snake and Clearwater river basins and 78 percent of normal above The Dalles Dam.

 

Although rainfall has been skimpy in the Columbia River basin, water flow will remain sufficient to maintain the chum operations, at least for the next 10 days. The short-term weather (5-day) forecast includes some but not a lot of precipitation, the longer 10-day forecast looks better. “The good news,” Baus said, “is that we’re finally getting some precipitation to the basin.”

 

Flows at Bonneville are currently at about 128,000 cubic feet per second and that is expected to change slightly with a 10-day flow forecast of 128 kcfs to 140 kcfs (see NOAA’s River Forecast  Center at https://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?id=BONO3).

 

Also see:

 

-- CBB, November 2, 2018, “ESA-Listed Chum Salmon Arrive Early Below Bonneville Dam; Flow Operations Begin To Protect Spawning,” http://www.cbbulletin.com/441754.aspx.

 

--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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