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.
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
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.
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.
of us would prefer not to live through last winter again,” said Tom Lorz of the
Columbia River Inter-Tribal Fish Commission.
that may be the case, said Steve Hall of the Corps’ Walla Walla District.
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.
gas levels stirred up by water plunging into dam tailraces can negatively
affect fish and other aquatic life.
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
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.
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.
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.
emergency releases were a collaboration of the Nez Perce Tribe, the U.S. Fish
and Wildlife Service and Idaho Fish and Game.
CBB, March 24, 2017, “Dworshak Management Balances Downstream Flooding, Making
Room For Future Runoff, Fish Releases,” http://www.cbbulletin.com/438581.aspx
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
is now expected to be back in service by July 1, 2018,” Halls said.
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
February 10, 2017, “TMT Continues Dworshak Combined Generation/Spill; Water
Supply In North Fork Clearwater Downgraded,” http://www.cbbulletin.com/438304.aspx
February 3, 2017, “With Dworshak Generation Down, River Managers Balance
Runoff, Flood Control Targets, Dissolved Gas,” http://www.cbbulletin.com/438280.aspx
September 23, 2016, “Dworshak Oil Spill Into North Fork Clearwater Slows
Turbine Overhaul, Cleanup Continues,” http://www.cbbulletin.com/437598.aspx
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
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