All three generators at Dworshak Dam tripped
off Tuesday, July 24, at 11 a.m. and, although one generator, Unit No. 1, the
largest of the dam’s generators, was back online within a couple of hours, the
other two were not restored until 10 p.m. Tuesday night, according to Alfredo
Rodriguez of the U.S. Army Corps of Engineer’s Walla Walla District.
With just one generator running, the Corps
passed only 5,500 cubic feet per second of Dworshak’s cool 45 degree Fahrenheit
water, causing warming in the hatcheries downstream of the dam, located on the
North Fork of the Clearwater River, as well as an anticipated warming of
tailwater temperatures at Lower Granite Dam.
The outage was repeated yesterday afternoon
(Thursday, July 26), according to a Corps email. Flows dropped to 3.2 kcfs of
spill but the problem was resolved and flows are back up to 12.9 kcfs.
Several days prior, with blistering air
temperatures expected in the Snake River basin, water temperature began rising
in the Lower Granite Dam tailwater, so the Corps increased the outflow of
Dworshak’s cold water Sunday, July 22, from 10.5 kcfs to 12.9 kcfs. The cold
water takes three days before it reaches Lower Granite. With the 12.9 kcfs, the
Corps saw a temperature improvement at Lower Granite, Rodriguez said.
The upper temperature limit allowed by the
Federal Columbia River biological opinion for salmon and steelhead in Lower
Granite Dam’s tailwater is 68 F. The maximum limit, among other things, helps
to protect Snake River sockeye salmon which are listed as endangered under the
federal Endangered Species Act.
Rodriguez said the Corps had to evacuate the
powerhouse for the first two hours of the outage due to a CO2 alarm, but once
that was over Corps personnel immediately set to work to get the generators
back on line while at the same time bringing flows from the dam back up to 12.9
That included spilling water and at one point
total dissolved gas in the dam’s tailwater rose to nearly 125 percent (110
percent is the Washington state water quality standard). TDG limits are
intended to protect young fish from gas bubble trauma in the dams’ tailraces
As a result of the sudden outage, water
temperature at the Nez Perce hatchery downstream from the dam on the Clearwater
River rose by 10 degrees, threatening juveniles as well as steelhead kelts,
according to Jay Hesse of the Nez Perce Tribe. Kelts are spawned Snake River
steelhead that are being reconditioned at the hatchery and will be released for
“We were not notified that there would be a
10K reduction in flow,” Hesse said, adding that a heads-up would have helped
the hatchery prepare. The reduction in flow and increase in temperature, he
continued, brought the hatchery to “the threshold of not being OK.”
Hesse suggested the Corps and hatchery
managers work together to determine how to communicate if such an event occurs
Rodriguez indicated that Corps models show
there will be a small spike upwards above the 68 F threshold water temperature
in the Lower Granite tailrace until Dworshak’s colder water reaches the dam,
but then temperatures will quickly fall back below 68 F.
“We had 10 hours with just one unit running
and we set up a schedule to gradually get flows back up to 12.9 (kcfs)” to
protect the migrating endangered sockeye in the Snake River, Rodrigues said.
“We did a heck of a good job on this.”
He said the Corps is still uncertain what
caused all three generators to trip, but some speculation is pointing to either
a transmission issue or a relay.
Migrating adult sockeye hit a thermal block in
2015 as river temperatures rose considerably above the 68 F limit set by the
BiOp. Some 90 percent of sockeye died before reaching Ice Harbor Dam, the lower
of the four Snake River dams. Idaho Department of Fish and Game, NOAA Fisheries
and the Nez Perce Tribes set up a rescue project at Lower Granite Dam to trap
the adults and haul them to the Eagle Hatchery.
As of Thursday morning, July 26, Dworshak
outflow was 13 kcfs, with 9.7 kcfs of that flow through turbines and 3.2 kcfs
being spilled. TDG was at 108.1 percent. The reservoir level is at about 1,578
feet in elevation and the Corps is aiming for 1,535 feet at the end of August,
according to Rodriguez. The tailwater temperature at Lower Granite was 66.93 F.
Air temperatures near Lewiston, Idaho will
continue to be in the upper 90s and Sunday will hit 100 F and Monday 104 F,
according to NOAA’s Weather Service.
--CBB, July 13, 2018, “With Temps Rising,
Corps Cools Snake River With Dworshak Water To Aid Endangered Snake River
--CBB, April 1, 2016, “Corps Report On 2015
Columbia/Snake Warm Water, Fish Die-Off Will Discuss Actions To Avoid Repeat,” http://www.cbbulletin.com/436358.aspx
-- CBB, September 11, 2015, “Snake River
Sockeye: Lowest Return Since 2007, Captive Broodstock Program Increases
-- CBB, June 12, 2015, “NOAA Fisheries
Releases Snake River Sockeye Salmon Recovery Plan: 25 Years Of Actions At $101