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New Court-Ordered Spill Regime Based On Dissolved Gas Caps Begins This Week
Posted on Friday, April 06, 2018 (PST)

Spring spill to aid juvenile salmon and steelhead migrating past lower Snake River dams began this week with a twist: instead of a designated target spill at most of the four dams, as was the case last year, the new court-ordered spill target will be to the maximum total dissolved gas levels allowed by state water quality standards, known as gas caps.


A three-judge panel ruled Monday in favor of an April 2017 U.S. District Court injunction allowing more spring spill at eight lower Snake and Columbia river dams. With the decision, spill to the gas cap began April 3 at lower Snake River dams and it will begin April 10 at lower Columbia River dams.


The plea for more spring spill to the gas cap was brought to District Court Judge Michael H. Simon in January 2017. Simon agreed that more spring spill would benefit ESA-listed fish, but delayed the action until 2018 while federal agencies completed a spill plan for lower Snake and Columbia river dams. That plan was submitted to the court Dec. 8, 2017 and Simon affirmed the plan in a January 8 order.


Simon’s final spring spill order is at


The plan changes spring spill at Lower Granite Dam from a spill target of 20,000 cubic feet per second day and night ( to the U.S. Army Corps of Engineers’ target gas cap spill of 45 to 47 kcfs, which is producing a TDG level in the tailrace of the dam of about 118 percent, according to Dan Turner of the Corps. Turner spoke to the interagency Technical Management Team Wednesday, April 4.


The allowable gas cap level downstream of the tailrace of Lower Granite Dam at Little Goose dam’s forebay (on the upstream side of Little Goose) is 115 percent, but it will take 3.5 days of travel time before higher gas levels reach Little Goose’s forebay. Lower Monumental and Ice Harbor dam forebay TDG level increases also will need to wait some 2.8 days for Little Goose and 2.9 days for Ice Harbor.


At Little Goose the change is from spilling 30 percent of the river day and night to a daily average spill target of 42 kcfs, which is producing about 118 percent TDG in the dam’s tailrace.


At Lower Monumental spill will change from last year’s gas cap spill day and night with targets ranging from 20 to 29 kcfs to this year’s daily average spill of 40 to 43 kcfs. It was at 41 kcfs Wednesday, which is producing TDG levels around 116 percent, Turner said.


Ice Harbor spill had a two-tiered spill schedule. April 3 to April 28 last year called for 45 kcfs daytime spill and spill to the gas cap at night. April 28 to June 20 called for 30 percent of the river to be spilled day and night. That is changing to a target daily average spill of 90 kcfs, although as of April 4, spill was at 62 kcfs, producing TDG of 115 percent.


Simon, in his order, also approved earlier PIT-tag monitoring of juvenile salmon, beginning March 1 (the monitoring is one month earlier than the timing called for by NOAA Fisheries’ 2014 biological opinion for the Federal Columbia River hydroelectric System). The monitoring is underway at three of the dams – Little Goose on the Snake River, and John Day and Bonneville on the Columbia River.


Percentage caps on total dissolved gas (caused when spill plunges into the river) are intended to protect young fish from gas bubble trauma during spill.


Also at the TMT meeting, Paul Wagner of NOAA Fisheries said that transportation at Snake River dams will begin April 23, with collection of juveniles beginning April 23 and the actual barging beginning the following day, April 24.


The Independent Scientific Review Board has said that when it comes to leaving juveniles in the river or transporting them the best option is to spread the risk, Wagner said, and that means about 50 percent of the fish should be transported. “Over half of the fish have generally passed by May 1,” he added.


According to the 2017 Fish Passage Plan, 50 percent of yearling chinook juveniles had passed Lower Granite Dam in 2016 by April 26, while 50 percent of subyearling chinook passage was by June 9. The 10-year median for subyearling passage is May 9 and for subyearlings June 1.


The median for 50 percent passage of unclipped steelhead is May 20 (passage last year reached 50 percent May 2): for hatchery steelhead the 10-year median 50 percent passage is May 4 (last year it was April 26), for coho May 15 is the 10-year median (last year it was May 8), and for sockeye the 10-year median is May 19 (last year it was May 22).


Also see:


--CBB, March 23, 2018, “Ninth Circuit Hears Arguments On More Spill For Juvenile Salmon/Steelhead At Columbia/Snake Dams,”


- CBB, December 8, 2017, “Briefs Filed In Appeals Court To Expedite Challenge To Increased Spill For Juvenile Salmon, Steelhead,”


-- CBB, June 23, 2017, “Litigants In Salmon BiOp Case Working Together To Develop Court-Ordered Spill-For-Fish Plan In 2018,”


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