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.
that is soon to change as the weather forecast calls for cooling air
temperatures later this weekend.
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.
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.
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.
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.
said Sunday air temperatures are expected to drop to about 93 degrees with
thunderstorms, and the area will see even lower temperatures next week (http://forecast.weather.gov/MapClick.php?lat=46.4091851&lon=-117.00815199999988#.WYyUUFGGPIV).
not a dramatic difference in flows, but there is some desire at the hatcheries
to get some relief,” said Paul Wagner of NOAA Fisheries.
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
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
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.
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.” http://www.nwd-wc.usace.army.mil/tmt/agendas/2017/0809_Port_of_Clarkston_Rev_SOR.pdf
washout from the Grand Ronde River in the spring (http://www.nwd-wc.usace.army.mil/tmt/agendas/2017/0809_Attachment_A_4-14-17_What_happened_to_the_highway.pdf) 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.
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).
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
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 (http://www.nwd-wc.usace.army.mil/dd/nwdp/project_hourly/webexec/rep?r=dwr&ago=0). That results in
TDG levels of 118 to 120 percent (http://www.nwd-wc.usace.army.mil/ftppub/water_quality/dwqi.txt).
CBB, July 21, 2017, “Dworshak’s Largest Turbine Out Another Year; Poses
Challenges For Salmon Management,” http://www.cbbulletin.com/439312.aspx
March 17, 2017, “Precipitation, Snowmelt Has River Operators Working To Control
Water Flow Through Mainstem Dams,” http://www.cbbulletin.com/438533.aspx