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River Ops Review 2017: Big Runoff, Involuntary Spill, Elevated Gas Levels, Quicker Fish Migration
Posted on Friday, December 22, 2017 (PST)

High flow, involuntary spill, high dissolved gas and early migration of juvenile salmon and steelhead mark mainstem Columbia/Snake river 2017 winter/spring operations.


Rain and runoff in the Snake River basin in late winter and spring this year resulted in high flows, involuntary spill and, at times, high total dissolved gas (TDG) all the way downriver to Bonneville Dam.


In general, Oregon and Washington water quality standards call for TDG of 110 percent and some biologists believe that fish could be subjected to gas bubble disease at higher levels.


Precipitation in the Clearwater River basin was 224 percent of normal in March, driving Snake and Clearwater river runoff at Lower Granite Dam up to 8.5 million acre feet in March alone, which was 254 percent of normal, according to Dan Turner of the U.S. Army Corps of Engineers.


Overall, the April to July runoff volume was 145 percent of normal, about 29 MAF, at Lower Granite, the upper of the four lower Snake River dams.


In addition to Turner’s assessment of runoff, flow and spill in 2017, Brandon Chockley of the Fish Passage Center ( described how the higher flows and more spill rushed salmon and steelhead downriver slightly earlier than the 10-year average. He said that looking at runoff January to July at Lower Granite, the year was ranked ninth of 89 years of recordkeeping.


Turner and Chockley spoke at the Technical Management Team’s Year End Review, December 12, in Portland, recapping this spring’s lower Snake and Columbia river flow and total dissolved gas levels, as well as juvenile passage through the lower Snake and Columbia river dams.


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 and Chockley’s presentations were among nine reviewed in the day-long session. Go to to see all presentations.


The high flows scoured river banks bringing debris downriver where it was trapped in lower Snake dam forebays, he said, and that had an impact on juvenile salmon and steelhead (separator mortalities and transport loading mortalities), as well as on generation, as generators were shut down while forebays were swept clean of the debris.


The 2017 Fish Operations Plan (FOP) calls for spill at Lower Granite of 30,000 cubic feet per second daytime and 18 kcfs nighttime beginning in early April: this year that would have resulted in total flow of about 110 – 115 kcfs.


However, involuntary spill March through June at times dwarfed that flow. At one time in mid-March Lower Granite saw 192 kcfs of water, but that dropped quickly as the region dried out and as the snowpack diminished in late June. By August 12, the dam was operating at minimum generation levels.


Little Goose Dam on the Snake River was hit hard by debris. At one point in early May two of the dam’s four units were taken out of service while Corps workers raked trash and debris from forebay screens. FOP spill at Little Goose is the lesser of 30 percent of the river or a spill cap based on holding total dissolved gas at or below 120 percent. Involuntary spill reached about 180 kcfs in early March, whereas FOP spill would have been closer to 120-125 kcfs. TDG in early May and in early June rose to over 130 percent.


Lower Monumental Dam, also on the lower Snake River, was similar: TDG reached about 127 percent in early May and again in early June.


In both cases – Little Goose and Lower Monumental – a gas spill cap was not attainable during involuntary spill, Turner said.


McNary Dam on the Columbia River had a similar profile, with FOP calling for daytime spill of 40 percent of the river and 50 percent at night, beginning in early April. That would have resulted in flows close to a peak of 350 kcfs. However, involuntary spill beginning the first part of March drove flows up, peaking twice over 450 kcfs.


For two weeks in early April, TDG at McNary was 124 to 129 percent, and from May 7 to 16, TDG was 129 to 130 percent.


TDG at the John Day Dam was 136 percent from May 8 to May 11. FOP spill at the dam is 30 percent of the river in the daytime and 40 percent at night.


With spill exceeding FOP, conditions in the river created higher TDG than is allowed by Oregon and Washington water quality standards. However, the flows helped to speed juveniles migrating downstream so that passage at all of the dams was slightly earlier and quicker than in lower flow years, Chockley said.


Juvenile timing is affected by the timing of hatchery releases -- some hatcheries in the Clearwater and Snake rivers released spring chinook juveniles and a few steelhead about a month early -- flows, temperature, spill volume and survival, Chockley said.


At Lower Granite Dam, yearling chinook and steelhead arrived earlier and, since transportation doesn’t begin until May 1, about 56 percent of the chinook and 58 percent of the steelhead had already passed Lower Granite when barging began. Subyearling chinook also arrived about a week early. Even after May 1, only about half of the remaining juveniles hitched a ride downstream.


Sockeye arrived in two batches, but Chockley said those arriving in April were likely kokanee that escaped Dworshak reservoir while the dam was spilling water in March and April. Hatchery releases of sockeye didn’t begin until April 19 and the first PIT-tagged sockeye smolt didn’t show up at Lower Granite until April 30. The first detection of a wild sockeye was May 6.


In the mid-Columbia where runoff ranked eighth in the last 89 years (The Dalles Dam), McNary Dam passage saw the same basic pattern, Chockley said, with 50 percent of the fish passing the dam by about May 6, while the 10-year average for 50 percent passage is closer to May 14. Steelhead were also about a week early and sockeye were slightly early, but closer to the 10-year average.


The 50 percent and 90 percent passage marks for yearling chinook at Bonneville Dam were about a week earlier than the 10-year average, as was steelhead. Sockeye were about 10 days ahead of average for both the 50 percent and 90 percent passage marks.


Lower Granite had the highest mortality for both subyearling chinook and coho juveniles in the last 10 years, Chockley said. Steelhead mortality at McNary was the highest in the last 10 years, as was sockeye mortality at Rock Island Dam on the upper Columbia River. Lamprey had the lowest mortality in the last 7 years at McNary and Bonneville dams.


Yearling chinook suffered the highest descaling in 10 years at Little Goose, while coho had the highest descaling in 10 years at John Day Dam. Coho and steelhead had the lowest descaling in 10 years at Rock Island.


Subyearling chinook and steelhead had the highest incidence of injury in nine years at Lower Granite: yearling chinook and coho had the second highest. Lamprey had the lowest injury rate in six years of data at McNary. Most injuries for salmon and steelhead are fin injuries, which the FPC defines as any cut or abrasion, laceration, swelling or other injury to the fins, Chockley said.


TDG monitoring was done at six projects: Lower Granite, Little Goose and Lower Monumental on the Snake River, and Rock Island, Bonneville and McNary dams on the Columbia River.


Criteria, according to Chockley, for reducing spill would be when more than 15 percent of juveniles show signs of bubbles on fins or 5 percent show severe signs of gas bubble trauma (GBT). Even considering the extended spill from Dworshak Dam, while some fish showed signs of GBT at Lower Granite Dam, severity was low and it was still below the 15 percent criteria.


TDG at Little Goose was 120 percent most of the spring and it was higher than 115 percent in the Lower Monumental forebay, rising to 132 percent May 10. One fish sample exceeded the 15 percent criteria and, although spill should have been stopped, it was impossible with the amount of flow in the river.


McNary had three of 33 fish with GBT, but all were of low severity.


Some 24 of 33 samples at Bonneville had signs of GBT, but all were low level.


Over 20 years of sampling for GBT, just 35 of 2,771 fish (1.3 percent) have exceeded the action limit, Chockley said. Of 303 samples collected when TDG was over 125 percent, just 27 (8.9 percent) exceeded the GBT limits.


Also see:


--CBB, February 3, 2017, “With Dworshak Generation Down, River Managers Balance Runoff, Flood Control Targets, Dissolved Gas,”


--CBB, December 22, 2016, “Year-End Assessment Matches 2016 Water Supply, Stream Flow, Fish Conditions With Juvenile Migration,”


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