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River Operations in Review: Balancing Spill For Juvenile Salmon With Adult Passage At Little Goose
Posted on Friday, January 11, 2019 (PST)

At one point last spring, the level of court-mandated spring spill designed to aid downstream passage of juvenile salmon stalled the passage of adult salmon at Little Goose Dam on the lower Snake River.


The fix, according to the interagency Technical Management Team at its meeting in late May 2018, was to balance spill for juvenile salmon with reduced spill to encourage spring chinook salmon “lost” in the Lower Monumental Dam pool downstream to move up and pass Little Goose Dam.


The problem in both 2017 and 2018 was a disparity between the number of fish passing Lower Monumental and those expected to pass the next dam upstream, Little Goose Dam, and the culprit was too much spill. In fact, there were about 6,000 to 7,000 fewer fish than expected at Little Goose, Doug Baus of the U.S. Army Corps of Engineers told TMT at its year-end review of river operations last month.


Baus was one of four speakers addressing the issue of Little Goose Dam in the day-long session and was among four speakers covering the lessons learned from the altered operations at the dam. Others included Eryck Van Dyke of the Oregon Department of Fish and Wildlife, Daniel Deng of the Pacific Northwest National Laboratories and Paul Wagner of NOAA Fisheries.


TMT is made up of fisheries and hydro/reservoir managers from state, federal and tribal agencies. Every December the group looks back at actions taken during spring and summer in managing Columbia and Snake river federal hydro/fish operations.


The additional spring spill to state TDG limits, known as gas caps, was mandated at lower Columbia and Snake river dams by an April 2017 order from Judge Michael H. Simon of the U.S. District Court of Oregon. Simon had ordered 24-hour spring spill for one year, 2018 only, beginning April 3 at lower Snake River projects and April 10 at lower Columbia River projects, and ending June 20 on the Snake River and June 15 on the Columbia River.


The disparity in counts from one dam to the next upriver dam is why from May 30 through June 3 TMT changed operations at Little Goose to encourage the lost fish to move up into the dam’s fish ladders.


(See CBB, June 1, 2018, “River Managers Make Spill Changes To Improve Spring Chinook Adult Passage In Lower Snake,”


It was a complicated operation for several days that combined a reduction in daytime spill at Ice Harbor to encourage adult spring chinook to move to the dam’s fish ladders, along with a higher operating pool upstream to accommodate the reduced river flow through the dam, and then returning to the higher spill later in the day.


Care had to be taken when reducing spill because without spill juveniles can find their way past dams through the powerhouse and, according to Baus’ presentation, “Each juvenile powerhouse encounter reduces subsequent SAR by a relative 9-13 percent.”


The operation, which was also employed during spring spill in 2017, was to drop the spill level at the dam from 45 percent to 30 percent of the river from 4 am to noon, store the remaining inflow in the Little Goose pool above the 1 foot minimum operating pool (MOP) range of 633 feet to 634 feet as needed, depending on inflows.


From noon to 4 pm, spill was increased to pass the river’s inflow. From 4 pm to 4 am, spill was increased as needed to draft the Little Goose pool back to MOP while remaining under 130 percent total dissolved gas, which was a spill level of about 125,000 cubic feet per second. The TDG level of 130 percent is higher than that allowed by Washington and Oregon state standards of 125 percent.


Overall, the operation saw 26 hours when the pool level was above MOP, Baus said, adding that the experimental operation, which was in effect from May 30 to June 3, was successful.


“As spill was reduced, we saw more adults at the fish ladder,” researcher Deng told TMT at its review meeting.


In a study of 2018 fish passage at Little Goose, Deng and his associates found that adult fish prefer to enter the fish ladder during the daytime. Of 400 acoustic-tagged fish that made it to Little Goose, some 95.26 percent entered the fish ladder between 4 am and 7 pm.


From May 21 to 25 when the spill level at the dam was 35 to 40 percent of the river spilled, 30 to 50 percent of adults in the tailrace entered the fish ladder, and when spill was at 45 percent of the river May 25 – 29, just 20 percent of adults in the tailrace entered the fish ladder, Deng said.


After TMT ordered less daytime spill and spill was dropped to 30 percent, 40 to 65 percent of adults in the tailrace entered the fish ladder, and more of those fish entered the North Shore fish ladder than did at the South Shore fish ladder, he said.


Baus, in his presentation, said that in “the event there is the delay of adult chinook salmon in periods of high spill in 2019 going to 30 percent spill in a more timely manner and storing above MOP would likely reduce the delay of adult chinook salmon in the LGS tailrace.”


According to Wagner, spill at Little Goose to 45 percent of the river began by court order in 2005 and as “it got to early summer, the fish slowed down.” The fish between Lower Monumental and Little Goose should pass the upper dam within 3 days.


In addition, more fish experienced fallback during 2018 (9.8 percent) compared to the 2008 (3.9 percent) and 2013 (7.5 percent) studies, Baus said in his presentation


Baus’ and Deng’s presentations are at


Also see:


-- CBB, July 27, 2018, “Court-Ordered Spill Completed In June; Corps Sends Judge Last Of Three Reports Detailing Operations,”


-- CBB, June 8, 2018, “NOAA Fisheries Delivers First Court-Ordered Spring Spill For Fish Report; Shows Complex Operations,”


-- CBB, June 15, 2018, “Fish/River Managers Have Differing Interpretations On What ‘Spill To The Gas Cap’ Looks Like,”


--CBB, May 18, 2018, “Court-Ordered Spring Spill Now Moot As High Columbia/Snake Flows Forcing Involuntary Spill At Dams,”


--CBB, April 13, 2018, “Court Ordered Spring Spill For Fish Begins On Four Lower Columbia River Dams,”


-- CBB, April 6, 2018, “New Court-Ordered Spill Regime Based On Dissolved Gas Caps Begins This Week,”


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