temperatures in the Lower Granite Dam tailrace have been hovering around 68
degrees Fahrenheit and river and salmon managers took steps this week to hold
the temperature at or below the 68 F threshold to protect migrating endangered
adult sockeye salmon.
both Monday, July 10, and Wednesday, July 12, the interagency Technical
Management Team has been looking for ways to keep the river cool during a spell
of hot weather as the adult sockeye migrate towards central Idaho spawning
grounds. The cool water also benefits other migrating adult fish and juveniles.
settled this week on two actions to lower water temperatures: Increased river
flows from Dworshak Dam and removing two surface spillway weirs.
River sockeye were listed as endangered under the federal Endangered Species
Act in 1991.
temperatures in the area have continued to be hot – in the upper 90s – and that
has both dam operators and salmon managers at TMT worried about water
temperatures at lower Snake River dams that are rising at the same time that adult
sockeye are migrating upstream and subyearling fall chinook are migrating
downstream. Last week, TMT increased the output of cold 44 degree water from
Dworshak Dam from 8,800 cubic feet per second to 10 kcfs.
last week’s water temperature at Lower Granite’s tailrace was just slightly
above 66 degrees, that rose to just higher than the 68 degree threshold last
weekend as the area was hit with hot weather. The 68 degree F limit was set for
salmon in NOAA Fisheries’ 2014 biological opinion for the federal Columbia/Snake
River hydro system.
weekend, the U.S. Army Corps of Engineers, which operates Dworshak Dam on the
North Fork of the Clearwater River, took an additional step and raised the
dam’s output to over 10.5 kcfs when the temperature at Lower Granite Dam’s
tailrace rose to 68.6 degrees, where it remains today, Friday, July 14. (http://www.nwd-wc.usace.army.mil/tmt/documents/ops/temp/summer_ops.html).
takes about three days for Dworshak’s cool water to arrive at Lower Granite Dam
temperatures are expected to remain hot – 97 F to 98 F – through Saturday
before it cools off somewhat early next week, according to Steve Hall of the
Corps’ Walla Walla District. The high temperature Sunday will drop to 93 F, 92
F Monday and 91 F Tuesday.
Corps has been balancing flows from Dworshak with its efforts to keep total
dissolved gas levels under the water quality limit of 120 percent. TDG levels
at the dam have remained somewhere between 118.6 and 119.4 percent, Hall said.
See the Dworshak hourly TDG report at http://www.nwd-wc.usace.army.mil/ftppub/water_quality/dwqi.txt
year, releasing more than 4.7 kcfs from Dworshak requires the dam to spill
water and that drives up TDG levels. Balancing the amount of cold Dworshak
water needed to provide cooling at Lower Granite Dam with TDG limits
complicates how and when TMT releases Dworshak water this summer.
Dworshak Dam’s largest generating unit, is out of service and behind schedule
for coming back online. It is not expected to be in service until later this
year. At this point, the Corps is uncertain when that will be.
TDG levels are harmful to fish below the dam. The higher TDG also impacts
hatcheries downstream, although they are equipped with degassing equipment.
Still, TDG levels at the Dworshak National Hatchery downstream of the dam are
ranging from a relatively safe 103 to 103.7 percent, Hall said. TDG levels at
the hatchery are at http://www.nwd-wc.usace.army.mil/dd/common/dataquery/www/?s=eyJiYWNrd2FyZCI6IjdkIiwidGltZXNlcmllc0xpc3QiOlsiREhDSS4lLVNhdHVyYXRpb24tVERHLkluc3QuMUhvdXIuMC5HT0VTLUNPTVBVVEVELVJFViJdfQ==.
considering the balance of flow and TDG by the Corps at Dworshak, TMT chose at
its Monday meeting to retain flows at 10.5 or greater for now. Dam operators
will continue to balance that flow target with the upper TDG limit, Hall said.
TDG rises with warmer air temperatures and falls as it cools.
more contentious step for fishery managers was to remove the surface spillway
weirs at both Lower Granite and Little Goose dams. The immediate effect was to reduce the amount of warm water going over the spillway and instead put more water under the spillgate. That’s cooler water and so cools the river an additional degree.
weirs primarily provide safer passage downstream through the dam for migrating
juvenile salmon and steelhead. Right now most of the juveniles are migrating
subyearling fall chinook, according to Russ Kiefer of the Idaho Department of
Fish and Game. The weirs are generally removed each year about August 1, so the
action calls on the Corps to remove them a couple of weeks early.
managers worried that there was not enough information to fully understand what
the impact on the juveniles would be with their early removal.
there is insufficient data on temperature and depth to judge when to shut off
the use of surface weirs for the subyearlings,” Kiefer said. “I am optimistic
that we will have good information at some point, but the challenge we face is
this year” as he supported the weirs’ removal as soon as possible.
added that the temperature effect will also be felt through the dams downstream
of Lower Granite and Little Goose dams.
managers agreed, some more reluctantly than others due to the lack of
information, to shut the surface weirs down immediately.
Corps was able to make the change at Lower Granite Wednesday afternoon, since
opening and closing the weir at that dam is simple. However, removal at Little
Goose will require a full crew and about half a day’s work, according to the
Corps’ Julie Ammann. That weir cannot be removed until next week and its timing
will be contingent on staff availability, so the exact date is uncertain.
addition to the actions taken at TMT this week, Mary Mellema of the Bureau of
Reclamation said that the annual upper Snake River flow augmentation began
Tuesday this week.
amounts to 487,000 acre feet of water out of the upper Snake basin, as well as
from the Boise River and Payette River basins. Augmentation water from the
upper Snake will conclude by the end of July and water from the Boise and
Payette basins will conclude by the end of August, she said.
early season sockeye salmon forecast was 198,500 fish, with 1,400 of those
heading to the Snake River. However, the U.S. v Oregon Technical Advisory
Committee downgraded that forecast last week to just 90,400 fish. It is unknown
how many are Snake River fish.
at Bonneville as of July 12 was just 83,824 sockeye, fewer than expected.
Typically, half the run passes the dam by June 25. Last year on July 12, 331,073
fish had passed the dam and the 10-year average is 301,226.
fewer have made it as far as the lower Snake River. Some 329 sockeye had passed
Ice Harbor Dam, the lower of the four dams, by July 12. Last year the count was
792 and the 10-year average is 660. Just 135 had passed Lower Granite Dam by
July 12, the upriver of the four dams. Last year the count was 555 and the
10-year average is 526.
2015, temperatures soared in the river to over 70 degrees F, effectively
stalling sockeye adults that had made it that far upriver and setting in motion
a rescue operation by the Nez Perce Tribe and Idaho Department of Fish and Game
of trapping and hauling the fish to Eagle Hatchery.
more than 500,000 sockeye passed Bonneville Dam in 2015, just 4,000 of those
were destined for the Snake River’s Sawtooth Basin and even fewer completed the
long journey due to unusually low and warm water conditions, despite management
attempts to cool the water. Some 56 adults were trapped in the Sawtooth Basin
and 35 were trapped at Lower Granite and hauled to Eagle, Idaho.
CBB, December 4, 2016, “Post-Mortem 2015 Snake River Sockeye Run; 90 Percent Of
Fish Dead Before Reaching Ice Harbor Dam,” http://www.cbbulletin.com/435642.aspx
July 7, 2017, “Corps Begins Cool Water Discharges For Returning Snake River
Sockeye; Dam Passage Below Average,” http://www.cbbulletin.com/439224.aspx
June 9, 2017, “With Dworshak Maintenance Schedule Uncertain, Plans Made For
Providing Cool Water (Spill) For Sockeye,” http://www.cbbulletin.com/439058.aspx