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NW Fishletter #386, Oct. 2, 2018

[5] Experts Examine Snake River Temperatures to Help Fish

With the dog days of summer behind us, water temperatures throughout the Columbia River Basin are beginning to drop, bringing relief to migrating salmon and steelhead that rely on cool water for their survival.

That relief also means members of the Columbia Basin Technical Management Team (TMT)--an interagency group of dam operations and fish experts that discusses precise operating plans for U.S. Army Corps of Engineers dams--can take a breather.

After meeting at least weekly since January, the team cancelled its Sept. 5 meeting and will begin meeting every other week through much of the fall. One of their most complicated tasks--determining when and how much cooler water to release from the Clearwater River to best help migrating fish--is winding down for the year.

The Clearwater River--which can be 20 degrees cooler than Snake River water, or more--is held back by Dworshak Dam, a Corps facility that also produces power and helps prevent flooding.

Ann Setter, the Corps' lead biologist for the operations division in the Walla Walla District, said her agency began testing the idea of releasing cooler water from Dworshak back in 1991, when sockeye were petitioned for an Endangered Species Act listing. By 1995 it became standard practice. At the same time, scientists were also studying the impact of the dam on fall Chinook, and whether their outmigration was delayed by holding back the cold water.

The goal is to lower Snake River temperatures to 68 degrees or cooler, which minimizes warm water disease--or columnaris--in all fish species. "It's a bacteria that flourishes when temperatures get to the 68- to 70-degree and above range," Setter said.

She said releasing the cooler water from Dworshak has a lot of impact on temperatures at the Lower Granite Dam, and some influence on temperatures at Little Goose Dam. After that, the impact is steadily reduced as the Snake River makes its way to Ice Harbor Dam and then the Columbia River.

The decisions on how much to release and how much to hold back are based on modeling. "It's a challenge, and that's why they model daily," Setter said, adding, "It's a very busy time for them in hydrology upstairs to meet, what for us is a legal requirement."

But which fish should benefit? Should they save more cool water for later runs, or release more now to help those currently migrating? Should they focus on returning adults, or juveniles heading to the ocean?

"It's an interesting balancing act we do," Russ Kiefer, TMT member who represents the Idaho Department of Fish and Game, told NW Fishletter. "All the runs, including lamprey, are important and fit into our deliberations," he said.

Their decisions are based partly on which fish are currently migrating, and whether this year's run is small, and may need the extra boost. In mid- to late summer, many of their discussions involve Snake River sockeye, which were making a comeback until the disastrously low flows and warm water temperatures in 2015 set back progress.

Idaho's sockeye have some of the toughest migrating conditions of all Pacific Northwest salmon, with a journey of more than 900 miles that includes crossing eight major dams during the warmest months. "It's not that we value them more than other fish. But they are affected more, and they are endangered," Kiefer explained.

The TMT's decisions on how much water to release from Dworshak are also based on unknowns, such as forecasts for air temperatures that influence how warm the water will get, and how much water Idaho Power is releasing through Hell's Canyon Complex.

Ralph Myers, Idaho Power's water quality program supervisor, said in late July and August, the water coming into the Hell's Canyon Complex is usually warmer than what's being released, since the sun and heat warm the shallower river more than it does the deep reservoirs. Typically, water flowing into the complex ranges from 78.8 to 82.4 degrees, while the water flowing out is between 71.6 and 73.4 degrees. Without the complex, he said, the Snake River would be considerably warmer during those months.

Myers also noted that prior to Aug. 7, Idaho Power is providing 237,000 acre feet of water to augment flows for salmon runs in the lower Columbia River. After that, the water coming through the complex is due to demand for power, which goes up in the heat as people use air conditioning, and irrigators turn on pumps.

The variables influencing water temperature at Lower Granite Dam are many, and with climate change, the TMT's job could become even more challenging.

A recent study led by Daniel Isaak examining changing river temperatures concludes that while most Northwest rivers will continue to provide suitable salmon habitat for the foreseeable future, "it also appears inevitable that some river reaches will gradually become too warm to provide traditional habitats."

Isaak, a fisheries research scientist at the Rocky Mountain Research Center, told NW Fishletter that water temperatures in the largest rivers in the Northwest--like the Columbia and Snake rivers--appear to be getting warmer.

"The story is, pretty much, over the last 20 to 40 years, you can see a climate warming signal during the summer and fall months," he said. That includes the lower Snake River, he said. But, like other rivers, that trend has actually cooled in some locations--often just below highhead dams--where, like Dworshak, water is being used to cool the river water downstream.

"Many of them are having to release larger and larger amounts of cold water to try and mitigate the effects," Isaak said, adding, "Flows have also been getting lower in the summer, on average. It comes down to the local capacity managers have to change the knobs and dials on the system they're managing. Dworshak has people managing temperature by using models, and they're doing the best they can to keep below the temperature threshold."

High temperatures in the lower Snake River are nothing new, according to Joseph Saxon, a Corps spokesman, pointing to temperature data from the 1950s, prior to construction of dams on the Snake River. The Corps' data shows that temperatures exceeded 71 degrees every year from 1952 through 1957, including a high of 79 degrees on Sept. 19, 1956.

Water temperatures in both the Snake and Columbia rivers are now under scrutiny, as the Environmental Protection Agency works to develop a plan to improve warm water, which "sometimes approach the upper limits of tolerance for cold water fishes, including salmon and steelhead," the agency says.

The EPA, which is in charge of enforcing the Clean Water Act, notes that stream temperature is affected by many factors, including the natural variation in weather and river flow, the reservoirs behind dams which slow the river, increased temperatures in tributaries, water management by dams, diversions for irrigation, discharges by cities and industries, and climate change.

One example of the impact from tributaries is the Yakima River, a major Columbia River tributary that saw 12 of the 30 hottest river temperatures ever recorded at Prosser, Wash., this summer, according to a release from the Washington State Department of Ecology. For 12 days in July, the average temperature was 80 degrees. "Over the last four years, the rise in river temperatures is notable. In fact, 20 of the 30 warmest river temperatures recorded since 1990 at Prosser were from the years 2015 to 2018," the agency's release said.

Ecology is working with the Benton Conservation District, the Yakama Nation and the U.S. Geological Survey to identify the cool water refuges in the lower river to help preserve them for fish.

Similarly, the Corps is taking advantage of the cooler water released from Dworshak to both cool the Snake River and to aid migrating fish by using that water to lower temperatures at Lower Granite Dam's fish ladders. Installed in 2016, the modifications draw cooler water from 20 meters below the water and pump the water to the surface, where it's sprayed over the ladder. The changes have resulted in lower water temperatures in the fish ladder, and less temperature differentials between the ladder and the river.

IDFG's Kiefer said to add one more complication, holding back cold water, has actually slowed the growth of fall Chinook that spawn naturally in the lower Clearwater River, causing them to migrate later than other fall Chinook in the system. In response to this finding, the TMT also tries to retain enough of the cold water behind Dworshak to cool off the Snake once those subyearlings start heading downstream, he said. "This thing is a tangled web," he said. "You've got to think about all these different pieces."

Kiefer added the TMT's decisions on how much Dworshak water to release rely on the Corps' modeling, and explanations from its TMT representative, Steve Hall.

At the TMT's latest meeting on Aug. 29, Hall had good news for the group. Water temperatures at all of the locations near Lower Granite Dam were below 70 degrees and dropping, and most were below 68 degrees.

In addition, Idaho Power was releasing less water from the Snake River, allowing the cooler water to have a larger impact. Weather forecasts called for clear skies, with highs around 80 degrees and lows in the 50s and 60s. September looks to stay relatively cool.

As for operations at Dworshak Dam, Hall said, "We're planning to reduce discharge, so we prolong the availability of cool water." -K.C. Mehaffey

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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