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Tripped Generators At Dworshak Temporarily Interrupts Water Releases Cooling Clearwater, Lower Snake
Posted on Friday, July 27, 2018 (PST)

All three generators at Dworshak Dam tripped off Tuesday, July 24, at 11 a.m. and, although one generator, Unit No. 1, the largest of the dam’s generators, was back online within a couple of hours, the other two were not restored until 10 p.m. Tuesday night, according to Alfredo Rodriguez of the U.S. Army Corps of Engineer’s Walla Walla District.

 

With just one generator running, the Corps passed only 5,500 cubic feet per second of Dworshak’s cool 45 degree Fahrenheit water, causing warming in the hatcheries downstream of the dam, located on the North Fork of the Clearwater River, as well as an anticipated warming of tailwater temperatures at Lower Granite Dam.

 

The outage was repeated yesterday afternoon (Thursday, July 26), according to a Corps email. Flows dropped to 3.2 kcfs of spill but the problem was resolved and flows are back up to 12.9 kcfs.

 

Several days prior, with blistering air temperatures expected in the Snake River basin, water temperature began rising in the Lower Granite Dam tailwater, so the Corps increased the outflow of Dworshak’s cold water Sunday, July 22, from 10.5 kcfs to 12.9 kcfs. The cold water takes three days before it reaches Lower Granite. With the 12.9 kcfs, the Corps saw a temperature improvement at Lower Granite, Rodriguez said.

 

The upper temperature limit allowed by the Federal Columbia River biological opinion for salmon and steelhead in Lower Granite Dam’s tailwater is 68 F. The maximum limit, among other things, helps to protect Snake River sockeye salmon which are listed as endangered under the federal Endangered Species Act.

 

Rodriguez said the Corps had to evacuate the powerhouse for the first two hours of the outage due to a CO2 alarm, but once that was over Corps personnel immediately set to work to get the generators back on line while at the same time bringing flows from the dam back up to 12.9 kcfs.

 

That included spilling water and at one point total dissolved gas in the dam’s tailwater rose to nearly 125 percent (110 percent is the Washington state water quality standard). TDG limits are intended to protect young fish from gas bubble trauma in the dams’ tailraces during spill.

 

As a result of the sudden outage, water temperature at the Nez Perce hatchery downstream from the dam on the Clearwater River rose by 10 degrees, threatening juveniles as well as steelhead kelts, according to Jay Hesse of the Nez Perce Tribe. Kelts are spawned Snake River steelhead that are being reconditioned at the hatchery and will be released for spawning.

 

“We were not notified that there would be a 10K reduction in flow,” Hesse said, adding that a heads-up would have helped the hatchery prepare. The reduction in flow and increase in temperature, he continued, brought the hatchery to “the threshold of not being OK.”

 

Hesse suggested the Corps and hatchery managers work together to determine how to communicate if such an event occurs again.

 

Rodriguez indicated that Corps models show there will be a small spike upwards above the 68 F threshold water temperature in the Lower Granite tailrace until Dworshak’s colder water reaches the dam, but then temperatures will quickly fall back below 68 F.

 

“We had 10 hours with just one unit running and we set up a schedule to gradually get flows back up to 12.9 (kcfs)” to protect the migrating endangered sockeye in the Snake River, Rodrigues said. “We did a heck of a good job on this.”

 

He said the Corps is still uncertain what caused all three generators to trip, but some speculation is pointing to either a transmission issue or a relay.

 

Migrating adult sockeye hit a thermal block in 2015 as river temperatures rose considerably above the 68 F limit set by the BiOp. Some 90 percent of sockeye died before reaching Ice Harbor Dam, the lower of the four Snake River dams. Idaho Department of Fish and Game, NOAA Fisheries and the Nez Perce Tribes set up a rescue project at Lower Granite Dam to trap the adults and haul them to the Eagle Hatchery.

 

As of Thursday morning, July 26, Dworshak outflow was 13 kcfs, with 9.7 kcfs of that flow through turbines and 3.2 kcfs being spilled. TDG was at 108.1 percent. The reservoir level is at about 1,578 feet in elevation and the Corps is aiming for 1,535 feet at the end of August, according to Rodriguez. The tailwater temperature at Lower Granite was 66.93 F.

 

Air temperatures near Lewiston, Idaho will continue to be in the upper 90s and Sunday will hit 100 F and Monday 104 F, according to NOAA’s Weather Service.

 

Also see:

 

--CBB, July 13, 2018, “With Temps Rising, Corps Cools Snake River With Dworshak Water To Aid Endangered Snake River Sockeye,” http://www.cbbulletin.com/441108.aspx

 

--CBB, April 1, 2016, “Corps Report On 2015 Columbia/Snake Warm Water, Fish Die-Off Will Discuss Actions To Avoid Repeat,” http://www.cbbulletin.com/436358.aspx

 

-- CBB, September 11, 2015, “Snake River Sockeye: Lowest Return Since 2007, Captive Broodstock Program Increases Spawners,” http://www.cbbulletin.com/434944.aspx

 

-- CBB, June 12, 2015, “NOAA Fisheries Releases Snake River Sockeye Salmon Recovery Plan: 25 Years Of Actions At $101 Million” http://www.cbbulletin.com/434233.aspx

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