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
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
(www.fpc.org) 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 http://pweb.crohms.org/tmt/agendas/2017/1212_Agenda.html 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
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
In both cases – Little Goose and Lower
Monumental – a gas spill cap was not attainable during involuntary spill,
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
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.
--CBB, February 3, 2017, “With Dworshak
Generation Down, River Managers Balance Runoff, Flood Control Targets,
Dissolved Gas,” http://www.cbbulletin.com/438280.aspx
--CBB, December 22, 2016, “Year-End Assessment
Matches 2016 Water Supply, Stream Flow, Fish Conditions With Juvenile