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Dworshak Management Balances Downstream Flooding, Making Room For Future Runoff, Fish Releases
Posted on Friday, March 24, 2017 (PST)

Operators at Dworshak Dam in Idaho dropped flows over last weekend to help reduce the prospect of local flooding downstream in the Clearwater River and further down the Columbia River where water levels are at flood stage at Vancouver, Washington.

 

At the same time and taking advantage of the lower flows, less spill and lower total dissolved gas levels in the North Fork Clearwater River, hatchery operators downstream of the dam released smolting juvenile spring chinook to begin their migration to the ocean and are now releasing some steelhead smolts a month earlier than normal.

 

Thursday, March 16, the U.S. Army Corps of Engineers, which operates the dam, dropped outflow from 22,500 cubic feet per second to 12.5 kcfs, lowering Clearwater River water elevations by about one foot. Outflow at the dam had been at 22.5 kcfs since March 12 as the Corps had begun to reduce the surface elevation in the dam’s reservoir – a flood control precaution – to make room for spring runoff.

 

Inflows to the reservoir are already high due to heavy precipitation and snow melt from lower level mountains, peaking at 52.6 kcfs, according to the Corps. Precipitation in the North Fork Clearwater River basin, where the dam is located, was 214 percent of normal in February.

 

The next day, March 17, the Corps dropped outflow from 12,500 cubic feet per second to 7.5 kcfs for half a day and back up to 8 kcfs to reduce the chance of local flooding, but also to create lower flow and TDG levels that would allow safe conditions to release spring chinook smolts from hatcheries downstream.

 

However, the Corps is still aiming for an April 15 flood control elevation that could be as low as 1,445 feet, an essentially empty reservoir if the April early bird prediction of the basin’s water supply forecast of 3.17 million acre feet persists in the coming week.

 

With the lower outflow, the reservoir has been rising, not dropping to the flood control target, Steve Hall, Water Program Manager for the Corps’ Walla Walla District, told the interagency Technical Management Team at its conference call Monday, March 20. The reservoir elevation was at 1,528.6 Monday, which is 36 feet higher than the end of month flood control target. It was under 1,510 March 15.

 

“We have to move water,” Hall said. “We’re backed up against the wall with no other place to go” but to release more water from the dam.

 

The Corps increased outflow Monday afternoon by 2 kcfs per hour until it reached 25 kcfs later in the day.

 

See Dworshak inflow and reservoir level predictions at https://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?lid=DWRI1.

 

That will not relieve flooding either locally or in the lower rivers, according to the Corps’ Julie Ammon at TMT. There will still be a system flood emergency throughout the Columbia and Snake rivers. Yet flows are dropping off, she said, and all the Corps and Bureau of Reclamation storage projects, such as Dworshak and Brownlee Reservoir on the Snake River, must begin spring system flood management protocols.

 

Ammon said this latest push of water in the system is due to precipitation and low level snow melt. It is not a part of the spring runoff. “We’re back to drafting operations and preparing for the spring freshet,” she said.

 

With the lower flows and much lower TDG levels created by spill at Dworshak Dam over the weekend, the U.S. Fish and Wildlife Service and the Nez Perce Tribe released spring chinook juveniles from the Dworshak and Clearwater hatcheries, according to Jay Hesse of the Tribe.

 

With the lower flows, TDG in the hatcheries had dropped to under 100 percent, said Dave Swank of the Service at the TMT meeting. Degassing equipment at the hatcheries lower dissolved gas levels of the river water used in hatcheries. That compares with hatchery TDG levels of over 104 percent when Dworshak’s outflows were at 22.5 kcfs and TDG at the dam exceeded 120 percent. At 7.5 kcfs, TDG at the dam dropped to106 percent.

 

The operation at Dworshak Dam is complicated because the dam’s largest generator is being repaired. That generator accounts for more than half the generation. Consequently, most of the outflow is through spill, not generators, resulting in higher than acceptable TDG levels in the river and in the hatcheries downstream.

 

Clean Water Act rules allow a TDG level of 110 percent. Elevated gas levels stirred up by water plunging into dam tailraces can negatively affect fish and other aquatic life.

 

However, with the increase in flows Monday and a corresponding increase in dissolved gas in the river and in the hatcheries, Swank said the hatcheries are planning an early release of steelhead to move the fish out of the high TDG environment.

 

Emergency releases of 1.4 million steelhead at the Dworshak National Fish Hatchery began Monday to remove the fish from the supersaturated conditions in the hatchery, Swank said. The hatchery also released 1.6 million spring chinook Monday for the same reason.

 

By today, March 24, he said all steelhead at the Dworshak Hatchery will have been released upstream in traditional release locations a month early, released directly into the Middle Fork at the hatchery or moved into ponds at the hatchery supplied by reservoir water to mitigate for high gas levels. The 1.1 million fish in the protected ponds will be released on schedule in mid-April into the river at the hatchery.

 

“However, if reservoir water blended with river water does not adequately reduce gas saturation levels, these fish may need to be emergency released as well,” Swank said. “Long-term survival of these fish and the wild fish in the river is hard to estimate, given the early release timing and significant exposure to high saturation levels in the hatchery and in the river system locally and downstream as well.”

 

He said it took the collaboration of the Nez Perce Tribe, the Service and Idaho Fish and Game “to get the fish released and avoid potentially catastrophic losses.”

 

With the increase in flows from storage dams, flooding at Vancouver is predicted to stay above minor flood stage (16 feet) at around 17 feet at least through this week, according to the National Weather Service.

 

A National Weather Service hydrograph of the Columbia River at Vancouver is at http://water.weather.gov/ahps2/hydrograph.php?gage=vapw1&wfo=pqr. Moderate flood stage at Vancouver is 20 feet and major flood stage is at 25 feet. The highest crest was June 13, 1948 when the river reached a level of 31 feet. It hit 27.2 feet February 9, 1996.

 

High river levels are likely to stay with us through spring, according to a NOAA spring outlook, which is predicting moderate flooding this spring over southern Idaho in the Snake River basin. NOAA said Idaho this year had received its second highest recorded snowfall.

 

“Rapid snowmelt from rain storms on top of snowpack has already caused flooding at lower elevations of this region. How long the flooding could last and how intense it will be depends on future precipitation and temperatures,” a NOAA news release said (http://www.noaa.gov/media-release/spring-outlook-risk-of-major-flooding-in-north-dakota-moderate-flooding-in-idaho).

 

Overall in the region, the Columbia River InterTribal Fish Commission and the Oregon Department of Forestry are predicting below average temperatures and above average rainfall from April to June, while NOAA is predicting a more normal spring.

 

“Mountain snowpacks should generally peak at greater-than-average depths and slightly later than usual,” according to Pete Parsons in a March 16 forecast -- https://www.oregon.gov/ODA/programs/NaturalResources/Documents/Weather/dlongrange.pdf – meaning “cooler-than-average conditions should further delay the spring melt-off.”

 

April will bring rain and more snow in the mountains and lower than average temperatures. The month of May will bring below-average temperatures and precipitation ranging from about 150 percent of average along the coast to slightly below average across the eastern zones. Seasonal melting of mountain snowpacks should be delayed, Parsons said. Cooler and wetter conditions will continue into June.

 

CRITFC meteorologist Kyle Dittmer released a similar spring forecast, predicting slightly colder than average temperatures and higher rainfall. He predicted 105 percent of normal rainfall in April, 120 percent of normal in May and 110 percent of normal in June.

 

Also see:

 

--CBB, March 17, 2017, “Precipitation, Snowmelt Has River Operators Working To Control Water Flow Through Mainstem Dams,” http://www.cbbulletin.com/438533.aspx.

 

-- CBB, March 10, 2017, “Dworshak Reservoir Emptied To Prepared For Snow Melt; Snowpack Above Average Throughout Basin,” http://www.cbbulletin.com/438450.aspx

 

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