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Washington Ecology’s Draft EIS Raises Gas Cap To Allow More Spill For Fish At Columbia/Snake Dams
Posted on Friday, February 01, 2019 (PST)

A flexible spill agreement signed in December by federal agencies, states and a tribe promises additional spring spill to total dissolved gas limits, known as gas caps, beginning this spring at Columbia and Snake river dams. The additional spill is thought to aid juvenile salmon passage.


A part of the agreement is for states to change their TDG standards. Washington’s current standards call for a limit of 120 percent TDG in the tailrace of dams and 115 percent in the next downstream forebay. The state’s Department of Ecology is considering eliminating the forebay standard and raising the tailrace standard to 125 percent and it is currently in the process of completing its environmental impact statement for the changes.


TDG limits are intended to protect young fish from gas bubble trauma in the dams’ tailraces during spill.


Ecology has put the draft EIS out for review that it says would allow the additional spill over eight federal dams in the lower Columbia and Snake rivers.


“The move could help improve the survival of juvenile salmon migrating to the ocean, increasing the availability of food for the struggling Southern Resident orcas,” Ecology says.


Ecology is responsible for regulating the levels of dissolved gases in the dam water. This temporary change for the 2019-2021 spring spill seasons at the dams would test the potential benefits for fish passage when higher levels of dissolved gases, mainly oxygen and nitrogen, are allowed. Dam operators could increase the amount of water they spill over the dams to help fish migrating downstream, but unlike the additional spill of last spring, dam operators would seek higher spill levels without reducing power generation.


“Helping more juvenile salmon survive the journey to the ocean is one of many steps we want to take to protect and restore salmon. Our hope is this will also support the recovery and sustained health of our orcas,” said Washington Gov. Jay Inslee. “This is an important short-term action we can take to help inform our decisions about what will work over the long-term.”


Although spring and summer spill has to some extent been a part of Columbia and Snake river operations for years, more recently the initial request for injunctive relief for spring spill to gas cap levels was enjoined with an earlier case argued in U.S. District Court in Oregon. The initial case, heard by Judge Michael H. Simon, resulted in a May 2016 remand of the federal Columbia River power system biological opinion for salmon and steelhead listed under the Endangered Species Act.


The spill plea was initiated in January 2017 by plaintiffs in the original case, the National Wildlife Federation and the State of Oregon, among others. 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 the dams.


One of the issues for the Corps during the 2018 spring spill to gas caps was determining what the forebay TDG level would be if spill in the upstream dam saturates water to 120 percent TDG. There are too many variables that influence downstream TDG – barometric pressure, wind and temperature – so it is difficult to predict the forebay TDG, Dan Turner of the Corps told the Technical Management Team Dec. 19 at TMT’s end of year review.


Spring spill at the eight dams this year will occur at higher gas cap levels for 16 hours a day and at lower levels called performance standard spill for eight hours a day, according to the spill agreement. Each of the eight dams has its own spill levels (details are available in the 2019-2021 Spill Operation Agreement at


In general, higher spill would occur at times of day when power demand and prices are at their lowest. Spill levels would drop when more power is needed and when that power is most profitable – typically morning and evening hours. The operation would help passage of juvenile salmon when spill levels are high while keeping power generation losses due to the spill at a minimum.


“As always, science is our guide and we need to balance the potential benefits to juvenile salmon without too great of risk to other fish,” said Maia Bellon, director of Ecology. “We want to be intentional and informed about any actions that significantly alter this complex ecosystem.”


An environmental impact statement provides extensive information on current available science, research, and data related to total dissolved gas, Ecology said. Drafts of the environmental impact statement and short-term modification are available for public comment through Feb. 28 at


In addition, Ecology is holding two public hearings:


Wednesday, February 13, 2:30 PM

Washington State School for the Blind, Fries Auditorium (Old Main Building), 2214 East 13th Street, Vancouver.


Tuesday, February 19, 6:00 PM

Public hearing via webinar at 6 p.m. (register for the webinar at


After reviewing the comments, Ecology will release the final EIS and make a decision on the short-term modification.


Additional information on this proposal is available on Ecology’s blog at


In addition, Oregon is expected to ask the Oregon Department of Environmental Quality to raise TDG tailrace limits up to 125 percent.


The new flexible spill agreement will be in effect until federal agencies complete in 2020 a federal Columbia River power system environmental impact statement and biological opinion for salmon and steelhead listed under the Endangered Species Act.


In the interim, the agreement will be tucked into a 2018 BiOp NOAA Fisheries had planned to complete by the end of this year. That additional work will delay the BiOp to about March 2019.


Also see:


-- CBB, January 11, 2019, “Following Presidential Directive, Feds Shorten Columbia/Snake Hydrosystem EIS Schedule By One Year,”


-- CBB, December 21, 2018, “Parties Sign Agreement On Flexible Spill For Fish Passage At Columbia/Snake Dams,”

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