Maintaining court-ordered spring spill at
maximum state-allowed total dissolved gas levels, known as gas caps, at eight
federal dams continues to challenge the U.S. Army Corps of Engineers.
A three-judge panel of the Ninth Circuit Court
of Appeals ruled April 2 in favor of an April 2017 U.S. District Court
injunction allowing more spring spill at four lower Snake and four lower
Columbia river dams. With the decision, spill to the gas cap began April 3 at
lower Snake River dams and at lower Columbia River dams April 10. The
additional spill through June 15 is designed to aid migrating juvenile salmon
Nearly every day since the Corps began the new
spill regime at the dams, TDG levels have exceeded state water quality
standards – 120 percent in the dam’s tailrace and 115 percent in the downstream
dam’s forebay. Staying at those levels without at some point during the day
exceeding them is difficult, Dan Turner of the Corps’ River Control Center told
the interagency Technical Management Team at its meeting Wednesday, May 2.
Percentage caps on total dissolved gas (caused
when spill plunges into the river) are intended to protect young fish from gas
bubble trauma during spill.
The Corps has developed levels of spill –
spill targets – that it believes would result in the allowed TDG levels. Those
targets change as flow increases or decreases. For example, the spill target
April 20 at Lower Granite Dam was 45,000 cubic feet per second of spill. That
created TDG of 119 percent in the dam’s tailrace (within TDG limits), but it
was resulting in 116 percent TDG in Little Goose Dam’s forebay, which exceeds the
115 percent gas cap limit. These exceedances extended through April 28 until
river flows began to drop and the gas cap spill target dropped to 33 kcfs April
29, resulting in 115 percent TDG in both the tailwater at Lower Granite and the
forebay at Little Goose.
The same issues occurred at each lower Snake
and Columbia river dam, except at Bonneville Dam where there is no downstream
dam forebay (see Snake River overview table at
http://pweb.crohms.org/ftppub/water_quality/12hr/snake_river.html and Columbia
River overview table at http://pweb.crohms.org/ftppub/water_quality/12hr/columbia.html).
Generally, Turner said, water that goes
through the powerhouse passes TDG levels that existed in the forebay upstream,
but when water is passed over the spillway it creates more TDG.
As the Snake and Columbia rivers become
saturated with gas, calculating TDG from the tailwater at one project to the
forebay several days travel time to the next forebay can be daunting.
It’s not just spill. TDG reacts with the
atmosphere, Turner said, and so there are several other factors that contribute
to the levels of TDG in the river, as well: barometric pressure, temperature
and wind speed.
As a rule of thumb, as barometric drops, TDG
rises by up to 3 percent and it will drop again with a rise in barometric
Also a rule of thumb, Turner said, is that the
percent TDG will rise by 2 percent for every degree the water warms.
And then there is degassing by increasing wind
speeds. As wind picks up from zero miles per hour to 10 mph, TDG that is at 115
percent will decline by about 0.2 percent per hour, but as wind picks up even
more, its effect on TDG levels rises. A wind change from 0 to 20 mph will drop
TDG by 2 percent per hour and wind increases from 0 to 30 mph drops TDG 2.2
All of these elements contribute to the
difficulty of predicting TDG levels in the river and it will continue to change
as flows are expected to increase in the coming week to levels that could
result in uncontrolled spill (spilling more water than desired to maintain TDG
at gas caps because power house capacity has been reached and more water has to
For example, as snow begins to melt, total
flow at Lower Granite, which on May 2 was about 107 kcfs, is predicted to rise
to about 140 kcfs by May 12, a big swing in flow in just one week.
The Dalles flow, which on May 2, was about 327
kcfs is predicted to rise to about 380 kcfs by May 12.
And, each dam is different.
“At McNary Dam, we initially thought that the
tailwater would control TDG in the river, but it’s not,” Turner said. “Looking
downstream four travel days to the John Day forebay, TDG was actually higher
and so the J.D. forebay became the controlling TDG” with spill at The Dalles.
“This is very different for us,” said the
Corps’ Julie Ammann. “There is a lot that is out of our control.”
One event this week was expected to drive TDG
even higher at Lower Granite Dam. On Wednesday, the day of the TMT meeting, all
water passing the dam would have to be briefly spilled as Bonneville Power
Administration was making emergency repairs at its substation in the area. That
repair called for shutting down all turbines at the dam, prohibiting passing water
through the powerhouse. The Corps
expected TDG to rise as high as 131 percent in the dam’s tailrace while repairs
Storing some water during the repairs in the
pool behind Lower Granite, allowing the reservoir to rise above minimum operating
pool (MOP), may have tempered the TDG impacts.
Finally, salmon managers at TMT requested a
change to the Corps’ spill priority list, moving The Dalles Dam to the top of
the list, meaning spill would be initiated at the dam first – before other dams
– when the system lacks load.
The spill priority list is used to reduce
generation when there is no market for the energy and the only option is to
increase spill within the hydrosystem, according to Paul Wagner of NOAA
“This often happens at this time of year when
flow is high and loads are low,” he said. “The spill priority list puts a
priority on where to put that spill as part of an effort to balance the TDG
created by the spill across the hydrosystem.”
The current priority for allocating spill
followed the sequence of Lower Granite, Little Goose, Lower Monumental, Ice
Harbor, McNary, John Day, The Dalles and Bonneville.
“The request to change that priority to put
The Dalles at the top of the list was in response to the desire to have The
Dalles spill more than it had been under the current operation when possible,”
Wagner said. That’s because The Dalles Dam is not fit with a bypass system for
juvenile fish and TMT’s salmon managers believe that when more spill is needed
in the system, it should begin at that dam.
BPA has said the additional spring spill to
gas cap levels will cost the power system as much as $40 million in lost
revenue this year because the water will be spilled and not used for
generation. This week BPA Administrator Elliot Mainzer in his quarterly
business review said the agency is studying a spill surcharge to recover the
cost increases resulting from the spill. He expects BPA to release a plan later
this month for public review. He mentioned during the conference call Tuesday,
May 1, that cost savings from Fish and Wildlife programs could be an element in
recovering those costs.
See more on BPA’s quarterly business review at
--CBB, April 13, 2018, “Court Ordered Spring
Spill For Fish Begins On Four Lower Columbia River Dams,” http://www.cbbulletin.com/440516.aspx
-- CBB, April 6, 2018, “Appeals Court Rules In
Favor Of More Spill For Juvenile Salmon, Steelhead At Columbia/Snake Dams” http://www.cbbulletin.com/440480.aspx
--CBB, April 6, 2018, “New Court-Ordered Spill
Regime Based On Dissolved Gas Caps Begins This Week,” http://www.cbbulletin.com/440479.aspx
--CBB, March 23, 2018, “Ninth Circuit Hears
Arguments On More Spill For Juvenile Salmon/Steelhead At Columbia/Snake Dams,” http://www.cbbulletin.com/440399.aspx
- CBB, December 8, 2017, “Briefs Filed In
Appeals Court To Expedite Challenge To Increased Spill For Juvenile Salmon,