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Temperatures To Cool In Lower Snake River, Riverboat Needs Higher Pool At Port Of Clarkston
Posted on Friday, August 11, 2017 (PST)

Daily high air temperatures have been hovering around 100 degrees Fahrenheit in Lewiston, Idaho, causing the lower Snake River to heat up to nearly 70 degrees F at the Lower Granite Dam tailrace this week despite continued releases of cold water from Dworshak Dam on the North Fork of the Clearwater River.


However, that is soon to change as the weather forecast calls for cooling air temperatures later this weekend.


Cold water releases from Dworshak Dam have kept water at the Snake River dam’s tailrace as cool as it is, but those releases are also elevating the level of total dissolved gas in the river below Dworshak dam (119 – 120 percent). The U.S. Army Corps of Engineers, which operates the dam, has been releasing water at a rate of 11,000 cubic feet per second, but due to an overhaul on its largest turbine, the majority of the water released comes from spill, which saturates the river with gas. That has been stressing juvenile salmon in the Dworshak National Fish Hatchery downstream. TDG in the hatchery, which uses water from the river, has remained consistently above 103 percent.


Hatchery operators have found some fish with gas bubbles in their gills, but are finding no abnormal mortalities and the fish continue to feed well, according to Dave Swank of the U.S. Fish and Wildlife Service. Still, a reduction in flows at Dworshak would be welcome, he said.


The Corps is shooting for a reservoir elevation behind the dam of 1,535 feet at the end of August, but the current output of 11 kcfs would overshoot that goal, said Steve Hall of the Corps’ Walla Walla District at the interagency Technical Management Team meeting Thursday, August 10. The current elevation, as of Thursday, was 1,561 feet.


As the air temperature in the area declines, Hall proposed dropping flows from Dworshak Dam to 10 kcfs Saturday at midnight and holding that flow until Lower Granite tailwater temperatures drop to 68 degrees or lower. He then asked TMT to consider a second drop in flows to 9 kcfs at its meeting next week.


Hall said Sunday air temperatures are expected to drop to about 93 degrees with thunderstorms, and the area will see even lower temperatures next week (


“That’s not a dramatic difference in flows, but there is some desire at the hatcheries to get some relief,” said Paul Wagner of NOAA Fisheries.


Few adult salmon and steelhead are affected by the current higher water temperatures. Russ Kiefer of Idaho Department of Fish and Game said that the agency is pretty confident that all endangered Snake River sockeye have passed Lower Granite.


Doug Baus of the Corps said that adult steelhead and fall chinook passage won’t pick up until September. However, some subyearling chinook salmon continue to migrate downstream.


What could impact migrating juveniles was a System Operational Request from the Port of Clarkston to raise the Lower Granite reservoir level one foot for 11 hours to accommodate a cruise boat visiting the Port next week.


The SOR asks to “Raise Lower Granite pool from Minimum Operating Pool (MOP) to MOP + 1 and hold for the 11 hour period from 0600 August 15, 2017 to 1700 August 15, 2017 before resuming normal operations.”


A washout from the Grand Ronde River in the spring ( filled parts of the Port with sediment, severely limiting space at its docks for cruise boats, an industry that brings about 27,000 people to the area every year. On August 15 there will be no space at the docks without raising the reservoir and the cruise boat arriving that day has agreed to stay just the 11 hours.


But providing the MOP + 1 level in the reservoir will take much longer and be more difficult than just adjusting for an additional one foot for an 11 hour period. An abrupt change to add the one foot would impact spill that aids juvenile passage, so the Corps suggested and fisheries managers agreed to take three days to raise the reservoir the one foot and also to take about three days to bring it back down to MOP, an operation that would be as close to “spill-neutral” as possible (meaning the total amount of spill would not be impacted).


The Corps announced in July that Dworshak’s largest turbine would be out of service for nearly another year, until July 1, 2018. Initially, the Unit-3 overhaul was to be completed July 15, 2017. Without the turbine, which accounts for more than half the dam’s power output, the Corps must spill more water for both summer and winter operations and that could mean higher than allowed levels of TDG.


Anytime flows at the dam need to be higher than 4.7 kcfs (the output of the dam’s two smaller turbines), the Corps will spill the additional water, raising the TDG levels in the river downstream. Currently, flows from Dworshak are made up of the 4.7 kcfs through the two small turbines, plus an additional 6.6 kcfs with spill ( That results in TDG levels of 118 to 120 percent (


Also see:


-- CBB, July 21, 2017, “Dworshak’s Largest Turbine Out Another Year; Poses Challenges For Salmon Management,”


--CBB, March 17, 2017, “Precipitation, Snowmelt Has River Operators Working To Control Water Flow Through Mainstem Dams,”


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