Snake River air and water temperatures are
remaining cool this week as operations at Dworshak Dam prepare to drop flows of
the dam’s cold water beginning Sept. 1 in order to preserve water for
Overall this summer, despite a string of
extreme temperature days and warm water flows at times from Idaho Power’s Hells
Canyon Dam, the temperature in the tailrace at Lower Granite Dam has remained
at or below the target temperature of 68 degrees Fahrenheit set by the 2014
salmon/steelhead biological opinion for the federal power system.
Much of the U.S. Army Corps of Engineers’
success at keeping river temperatures under control has been releases of cold
water from Dworshak Dam, located on the North Fork of the Clearwater River.
With Clearwater and Salmon river water
temperatures dropping, and releases from Hells Canyon Dam dropping, Steve Hall
of the Corps’ Walla Walla District told the interagency Technical Advisory
Committee at its meeting this week that flows from the dam will drop from the
current 7,500 cubic feet per second to 5 kcfs as of Sept. 1.
All is lining up for the transition: the water
temperature in the Lower Granite tailwater was about 67 degrees, the reservoir
was at an elevation of 1,537.4 feet the day of the meeting, Aug. 29, and “on
track to meet the 1,535 foot target by Aug. 31,” and the weather forecast is
clear and cool, with highs in the 80-degree range and lows into the 50s and
60s, he said.
“Things are cooling off nicely, so we will be
managing with less water,” Hall said.
Over the course of several days – Sept. 1 – 4
– the Corps will drop flows from Dworshak to about 5 to 5.5 kcfs.
Water temperatures below 68 degrees are
designed to aid salmon and steelhead passage, both adult and juvenile fish, at
the lower Snake River dams.
One of those stocks is the Snake River sockeye
salmon, listed as endangered under the federal Endangered Species Act.
According to Russ Kiefer of the Idaho Department of Fish and Game, the fish are
still arriving in the Sawtooth Valley. IDFG and the Shoshone Bannock Tribes
have now trapped 79 sockeye in the valley. Eleven of those are natural fish.
That’s an increase over the past week of 26 fish.
Last week at TMT, Kiefer said that by Aug. 20
each year 54 percent of the fish had been trapped. The 10-year average for
total trapped fish is 661.
Some 193,810 sockeye passed Bonneville Dam
this year, 60 percent of the 10-year average of 321,934 fish. Last year’s tally
at the dam was 87,678.
Fall chinook are slowly showing up at Lower
Granite, said Paul Wagner of NOAA Fisheries. Some 445 passed the dam as of Aug.
28. That’s 38 percent of the 10-year average of 1,180 fish. Last year on Aug.
28, 536 fish had passed.
As a precursor to what the run of fall chinook
might be in 2019, 49 fall chinook jacks have passed the dam, 27 percent of the
10-year average of 228.
Some 3,022 steelhead had passed Little Goose
Dam, apparently a better indicator of the current run since many steelhead will
hold downstream of Lower Granite, Wagner said. That’s 17 percent of the 10-year
average of 17,951 on Aug. 28. Last year’s passage on this date was 2,293.
Some 183 lamprey had passed Lower Granite,
much higher than the 10-year average of 40. Passage last year was 311. Lamprey
passage at Bonneville this year is 42,496, also far higher than the 10-year
average of 29,203, but lower than last year’s tally of 80,947 lamprey.
--CBB, August 24, 2018, “Lower Granite Water
Remains Cool; Snake River Sockeye Run Nearly Complete At 272 Fish,” http://www.cbbulletin.com/441376.aspx
--CBB, Aug. 10, 2018, “River Managers Opt To
Save Cool Dworshak Water For Upcoming Salmon/Steelhead Migration,” http://www.cbbulletin.com/441255.aspx