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NW Fishletter #372, August 7, 2017

[2] TMT Tries to Manage Dworshak Outflows to Cool Lower Snake River

Part 1

The U.S. Army Corps of Engineers began increasing outflow from Dworshak Dam July 6 to help cool the lower Snake River and aid adult salmon and steelhead migrating upstream to spawning areas.

The summer cooling operation is triggered at Dworshak when temperatures approach 68 degrees in Lower Granite Dam's tailwater and daily average water temperatures recently have hovered just above 67 degrees and reached 70 farther downstream at the temperature station at Anatone, Wash.

Salmon and steelhead don't like water temperatures much above 65.

With warm, dry weather forecast, the Corps models are showing river temperatures continuing to rise in coming days.

Meeting on July 5, the Technical Management Team agreed that the Corps should increase Dworshak outflow from 9 kcf to 10 kcf at beginning midnight July 5, which the Corps did.

The army agency and other TMT members are trying to maintain water temperatures at 67 degrees in the Lower Granite tailwater, and no higher than 68. The TMT guides hydro operations in the Snake and Columbia rivers.

With ample cool water behind Dworshak Dam this year, releasing it into the river sounds simple enough. But it's not so clear-cut. Confounding the operation is the need to release much of the water as spill.

Because Dworshak's Unit 3--the largest of three generating units--is down for repair, more water has to be released as spill, and more spill usually means higher levels of total dissolved gas (TDG) produced as water tumbles over the spillways and combines with air.

The Unit 3 remodel has experienced numerous delays and was slated for completion earlier this spring. Dam operators at the Corps' Walla Walla District obtained a short-term a waiver to release water that results in TDG as high as 120 percent, but not to exceed 121 percent. The normal limit is 110 percent TDG.

Both adult and juvenile fish are sensitive to spill levels. While spill aids juvenile salmon and steelhead passage through the Columbia/Snake system, too much can give them gas bubble trauma, a potentially fatal condition. Adult salmon and steelhead are also susceptible to gas bubble trauma.

Consequently, the salmon managers and other TMT members are attempting to balance cold water releases while maintaining spill TDG at no more than 120 percent.

The interagency TMT will hold a special meeting July 10, in case water temperatures or TDG levels rise, or if TDG or gas bubble trauma becomes a problem at the nearby Dworshak National Hatchery.

Jay Hesse, TMT member from the Nez Perce Tribe, said it wasn't simply a matter of prioritizing cold water or low TDG levels. The panel, he said, had to take into account all factors, including what's happening in the river with adults and juveniles and in the hatchery on a real time basis.

The current FCRPS BiOp and its required 2017 Water Management Plan require the cooling operation, referred to as summer flow augmentation, to protect Endangered Species Act fish originating in the Snake River.

Currently, endangered sockeye are migrating upstream and starting to pass lower Snake River projects. ESA-listed spring/summer Chinook and steelhead are continuing through the lower Snake on their way to spawning areas.

The returns of these Snake River summer salmon and steelhead are expected to be below 10-year averages this year.

As far as Snake River juvenile salmon and steelhead go, most have already passed lower Snake River dams on their way to ocean habitats. However, large numbers of sub-yearling Chinook migrants are still in the river as are the last of the juvenile steelhead.

Dworshak's troublesome Unit 3 is expected to return to service later this year. -Laura Berg


Efforts Continue to Cool Water in Lower Snake River--Part 2

With water temperatures above 68 degrees, dam and salmon managers continue searching for ways to cool water in the lower Snake River.

This time of the year, upstream migrating adult sockeye, spring/summer Chinook and summer steelhead are in the river, along with the last of the downriver migrating juvenile fall Chinook. Water temperatures above 68 degrees can be lethal to these coldwater fishes.

To protect the fish, the U.S. Army Corps of Engineers Walla Walla District has been releasing cold water from Dworshak Dam, most of it as spill because the dam's largest turbine is being reporpaired.

However, the high spill volume has created elevated levels of total dissolved gas downstream, which can be a problem for fish. The Corps had received a waiver to increase allowable TDG levels, but permissible levels have now been reached, so no more cooling water can be spilled from Dworshak.

Adding to the problem are current air temperatures along the lower Snake River, which are not expected to moderate any time soon. Both air temperature and the amount of daylight figure into river temperatures.

weir
How spillway weirs work. Credit: NOAA Fisheries

Finding other ways to help cool the water was the main topic of discussion at the July 11 Technical Management Team meeting.

Idaho Department of Fish and Game biologist Russ Keifer said it was especially important because salmon and steelhead runs are depressed this year.

"Between 70 and 100 percent of the Snake River sockeye run has passed Bonneville Dam by now," he said. "About 400 fish is all we have. Spring/summer wild Chinook numbers are down. Wild B-run steelhead are also down. The adult end of the equation is not very promising this year."

These salmonids have been designated as endangered or threatened under the Endangered Species Act.

Keifer proposed removing surface weirs at Little Goose and Lower Granite dams earlier than usual. Because the weirs are close to the surface, juvenile fish usually have an easier time finding the spillway. But without surface weirs, water goes through deeper, cooler spillways. The resulting cooler water, he argued, would help the passage of both adult fish and the remaining juveniles.

Keifer said spillway weirs were already less effective because juveniles were now moving down the water column to avoid overheated surface waters.

Doug Baus, a Corps TMT member, reminded his colleagues that the 2017 Fish Passage Plan, which operates under the current BiOp, allows for this in-season adaptation, but specifies a flat spill pattern and no change in the amount of spill.

Nonetheless, Keifer's proposal garnered many questions and concerns from TMT members, including:

  • How much temperature improvement would there be?
  • Was this action being done to save adults at the expense of juveniles?
  • With more cool and warm water mixing in the river, would the less temperature-stratified water column inhibit juvenile migration?
  • Would warmer temperatures build at fish-ladder exits?
  • Would the change in spill pattern at Little Goose Dam reduce the strength of the fish-confounding eddies that form below Little Goose Dam?
  • Could the weirs be put back in again this season?

The robust TMT discussion indicated that answers to most of the questions were unknown.

It was noted, however, that next year's installation of surface PIT-tag detectors and the temperature data analysis anticipated this fall from Pacific Northwest National Laboratory would, in the near future, help fish managers develop better criteria for making decisions about when to retract the weirs.

Despite some skepticism, TMT members voted for, or didn't oppose, early removal of surface weirs at the two dams. -Laura Berg


Early August Update

Even though current water temperatures hovering around 69 degrees at Lower Granite and Little Goose dams are higher than is good for fish, they have been lower than temperatures further downstream at Lower Monumental and Ice Harbor dams. Surface weirs have come out for the season, but it's not possible to say if coming out early helped cool the river near Lower Granite and Little Goose. The 11 kcfs discharges--more than half of it spill--from Dworshak Dam are more certain to have contributed to lowering water temperatures despite the recent soaring 100 F plus air temperatures. Total dissolved gas from the spilling water is currently maintained at 119 percent. -L. B.

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NW Fishletter is produced by Energy NewsData.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: Laura Berg
Phone: (206) 285-4848 Fax: (206) 281-8035

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