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Dworshak’s Largest Turbine Out Another Year; Poses Challenges For Salmon Management
Posted on Friday, July 21, 2017 (PST)

Dworshak Dam’s largest turbine will 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 U.S. Army Corps of Engineers must spill more water for both summer and winter operations and that could mean higher than allowed levels of total dissolved gas.

 

If flows from the dam, located on the North Fork of the Clearwater River, need to be higher than 4,700 cubic feet per second (the output of the dam’s two smaller turbines), the Corps will spill the additional water, raising the TDG levels in the river downstream.

 

This summer the Corps and fishery managers at the interagency Technical Management Team have found a balance between spill and the right amount of TDG (under 121 percent). However, saturated gas levels this last winter exceeded water quality limits when higher than normal flows in the North Fork of the Clearwater basin forced more spill and that forced hatcheries to release some juvenile steelhead and salmon early.

 

“All of us would prefer not to live through last winter again,” said Tom Lorz of the Columbia River Inter-Tribal Fish Commission.

 

Unfortunately, that may be the case, said Steve Hall of the Corps’ Walla Walla District.

 

“The turbine will be largely dismantled this winter, so no, it will be the same as last year,” Hall said, explaining that without the turbine in place there can be no flow through the Unit-3 power house and so when higher flows are needed the dam will need to spill more water.

 

Elevated gas levels stirred up by water plunging into dam tailraces can negatively affect fish and other aquatic life.

 

Unit-3 is the largest of Dworshak’s three turbines, rated at about 220 megawatts. Its outage limits the powerhouse capacity at the dam to about 45 percent of normal and also limits the amount of discharge from the dam to about 4.7 kcfs through turbines.

 

In March 2017, spill was causing high levels of TDG in the river that exceeded water quality limits and that was impacting juvenile salmon and steelhead in the Clearwater and Dworshak national hatcheries.

 

The Dworshak National Fish Hatchery began releasing 1.4 million steelhead March 20 to remove the fish from the supersaturated conditions in the hatchery. The hatchery also began releasing on the same day 1.6 million spring chinook for the same reason. The releases were a month earlier than normal.

 

Steelhead from the Dworshak Hatchery were either released upstream in traditional release locations, released directly into the Middle Fork of the Clearwater River 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 that were placed in the protected ponds were released into the river on schedule in mid-April.

 

The emergency releases were a collaboration of the Nez Perce Tribe, the U.S. Fish and Wildlife Service and Idaho Fish and Game.

 

See CBB, March 24, 2017, “Dworshak Management Balances Downstream Flooding, Making Room For Future Runoff, Fish Releases,” http://www.cbbulletin.com/438581.aspx

 

Refabrication in Austria of some parts needed for the turbine is in progress and on schedule. Hall said this work is moving along smoothly. Crews at the dam will wrap up work by the end of September and return in February to begin assembly when the parts arrive.

 

“Unit-3 is now expected to be back in service by July 1, 2018,” Halls said.

 

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

 

--CBB, February 10, 2017, “TMT Continues Dworshak Combined Generation/Spill; Water Supply In North Fork Clearwater Downgraded,” http://www.cbbulletin.com/438304.aspx

 

--CBB, February 3, 2017, “With Dworshak Generation Down, River Managers Balance Runoff, Flood Control Targets, Dissolved Gas,” http://www.cbbulletin.com/438280.aspx

 

--CBB, September 23, 2016, “Dworshak Oil Spill Into North Fork Clearwater Slows Turbine Overhaul, Cleanup Continues,” http://www.cbbulletin.com/437598.aspx

 

--CBB, May 13, 2016, “Needed Work, Low Flows At Dworshak Dam Pose Challenge As Water Needed For Juvenile Sockeye Migration,” http://www.cbbulletin.com/436712.aspx

 

--CBB, April 8, 2016, “Agencies Set For Spill Tests At Dworshak To Judge Impacts To Hatchery Fish During Generator Overhaul,” http://www.cbbulletin.com/436412.aspx

 

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