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Actions Continue To Aid Snake River Sockeye: Removing Spillway Weirs, Increasing Dworshak Flows
Posted on Friday, July 14, 2017 (PST)

Water 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.


Meeting 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.


They settled this week on two actions to lower water temperatures: Increased river flows from Dworshak Dam and removing two surface spillway weirs.


Snake River sockeye were listed as endangered under the federal Endangered Species Act in 1991.


Air 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.


Although 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.


Last 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. (


It takes about three days for Dworshak’s cool water to arrive at Lower Granite Dam


Air 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.


The 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


This 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.


Unit-3, 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.


High 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


After 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.


A 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.


The 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.


Salmon managers worried that there was not enough information to fully understand what the impact on the juveniles would be with their early removal.


“Currently, 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.


He added that the temperature effect will also be felt through the dams downstream of Lower Granite and Little Goose dams.


Salmon managers agreed, some more reluctantly than others due to the lack of information, to shut the surface weirs down immediately.


The 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.


In 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.


Augmentation 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.


The 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.


Passage 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.


Far 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.


In 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.


Although 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.


See, CBB, December 4, 2016, “Post-Mortem 2015 Snake River Sockeye Run; 90 Percent Of Fish Dead Before Reaching Ice Harbor Dam,”


Also see:


--CBB, July 7, 2017, “Corps Begins Cool Water Discharges For Returning Snake River Sockeye; Dam Passage Below Average,”


--CBB, June 9, 2017, “With Dworshak Maintenance Schedule Uncertain, Plans Made For Providing Cool Water (Spill) For Sockeye,”

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