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River Operations in Review: Environmental Factors Make Spilling To Gas Cap Tricky Business
Posted on Friday, January 11, 2019 (PST)

Every day, between April 3 and June 20 last year, the U.S. Army Corps of Engineers had to determine what amount of spill would bring the lower Snake and Columbia rivers up to state-mandated total dissolved gas limits while not exceeding those limits.


Dan Turner and Laura Hamilton, both of the Corps’ Reservoir Control Center, were charged with making the decision 79 times, 7 days a week during the spring of 2018.


The additional 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.


Maintaining spill at the gas cap, according to Turner, was difficult due to environmental factors that changed the gas saturation levels between spillways and forebays. Turner spoke to the interagency Technical Management Team at its year-end review of river operations last month, in Portland (his presentation is at


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.


Turner’s presentation was among nine reviewed in the day-long session.


The daily grind for the Corps began each day looking back at what happened the day before and then looking forward to what could be expected in river flow, air and water temperature, wind and barometric pressure changes, Turner said.


“We wanted to operate up to maximum spill that was up to but not exceeding water quality standards for the states of Washington and Oregon,” Turner said.


Oregon standards, he said, were 120 percent TDG in the dams’ tailraces with two hours not to exceed 125 percent TDG.


Washington’s TDG criteria are the most restrictive with 120 percent in the tailrace, but just 115 percent in the downstream forebay, all calculated on a rolling 12-hour average, a standard that was difficult to maintain, he said.


“We calculated for both state standards and figured out where the most restrictive locations would be,” Turner said.


The Corps had less control in the downstream forebays due to environmental factors. Those factors included:

-- barometric pressure – as pressure rose, so did TDG;

-- wind speed – the higher the wind speed the more degassing would occur, reducing TDG;

-- temperature, the higher the temperature, the higher the TDG.


Of the lessons learned, Turner said there is no one spill cap: “environmental conditions drove the train.” Another lesson is that it is not possible to keep TDG at a constant level as saturated water travels downstream.


“We have an imperfect understanding of how spill influences TDG and we have an imperfect understanding of how environmental factors will influence TDG,” he said.


The daily process was arduous, beginning with looking back at the data, flow and weather from the day before, and then looking at the weather and flow forecasts for the current day. With that information, the Corps estimated the maximum spill level for the day that meets but does not exceed the gas cap when considering the daily spill and TDG relationship, the forecasted environmental factors, the most restrictive gauge and water travel time (3.5 to 4.5 days between dams).


Then the Corps coordinated with NOAA Fisheries, notified each project (dam) and the Bonneville Power Administration about daily operations and posted the spill caps on the web.


In addition, the Corps coordinated weekly with TMT and each month reported to the District Court.


A Dec. 18 agreement signed by federal and state agencies and a tribe could make the process easier (see CBB, December 21, 2018, “Parties Sign Agreement On Flexible Spill For Fish Passage At Columbia/Snake Dams,”


Although start and end dates will be the same as last year, daily timing of the spill in 2019 will now be flexible as to dam and time of day in order to reduce costs to the Columbia River basin power system. The new agreement could be for as many as three years, or until federal agencies complete in 2021 a federal Columbia River power system environmental impact statement and biological opinion for salmon and steelhead listed under the Endangered Species Act (the completion date was changed this week to September 2020).


In the interim, the agreement will be tucked into a 2018 biological opinion NOAA Fisheries had planned to complete by the end of 2018. That additional work will delay the BiOp to about March 2019, according to NOAA spokesperson Michael Milstein. NOAA Fisheries personnel are currently on furlough due to the government shutdown and it is unknown at this point if the shutdown will cause further delays in completing the BiOp.


Agreeing to the new flexible spill regime are the states of Oregon and Washington, the Nez Perce Tribe, the Bonneville Power Administration, U.S. Army Corps of Engineers and the Bureau of Reclamation.


In addition, the states of Idaho and Montana reviewed the agreement and are supportive of the flexible operation, a federal agency joint statement said.


With the spring runoff at The Dalles Dam calculated at 118 percent of normal, not all spring spill at the dams was controlled. For a long period in May and early June, spill was involuntary and the river’s natural flow exceeded gas caps. Roughly, controlled spill to the gas cap at Snake River dams occurred April 3 to May 6 and June 3 to June 20. The period between May 6 and June 3 was involuntary spill. The exception was Ice Harbor Dam, which had controlled spill to gas caps April 8 to May 6 and June 8 to 10, and involuntary spill at other times.


Controlled spill at Columbia River dams was April 10 to 28 and June 7 to 15.


“There was quite a bit of snowpack heading into the runoff, especially up north,” said Julie Ammon, Chief of the Corps’ Reservoir Control Center, in her presentation to TMT ( “There was a lot of late precipitation in the headwater basins in April, and in May higher than normal temperatures triggered the runoff.”


Runoff at Lower Granite Dam in May was 149 percent of normal and the April through July water supply volume was 23.1 million acre feet, 116 percent of normal.


Runoff in May at The Dalles Dam was 176 percent of normal with an April through August water supply volume of 101 MAF, 116 percent.


She added that June was relatively dry and warm, and that later flows in the basin in June through August were below average.


Also see:


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


-- CBB, June 29, 2018, “Corps’ Second Spill Report To Court Details Impacts Of High Flows, Involuntary Spill In May,”


-- 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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