As the snow melt-off progresses and nears an
end in some areas, river flows in the Snake and Columbia rivers are declining
and so is involuntary spill at eight dams on the rivers that in May forced
total dissolved gas levels higher than Washington and Oregon clean water
Lower flow at most dams is allowing the U.S.
Army Corps of Engineers to begin to return to court-ordered spring spill up to state
mandated total dissolved gas levels, known as gas caps – 120 percent TDG in
tailraces and 115 percent TDG in the downstream dam’s forebay.
Higher than normal flows, spill and TDG that impacted
the spill cap operations in May are returning to lower levels, according to Dan
Turner of the Corps’ River Control Center, speaking at the interagency
Technical Management Team meeting Wednesday, June 6.
Even with falling stream flows (flow at Lower
Granite Dam on the Lower Snake River is 110,000 cubic feet, 10 percent below
the 30-year forecast), the water supply outlook through early summer is looking
good with forecasts at all major dams higher than the 30-year average.
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 and
With lower stream flows at Snake River dams,
the Corps is again managing to spill targets. It has now hit that target at
Lower Granite Dam (31,000 cubic feet per second) since June 3 and has kept TDG
levels at or slightly under gas cap levels since June 1. TDG in Lower Granite’s
tailwater reached 126 percent May 26 and 27. The Little Goose Forebay hit 120
percent May 28 and 29.
Flow on June 3 at Lower Granite was 110 kcfs,
but had been over 200 kcfs at one point in May. It is forecasted to drop
precipitously by July 1 to under 60 kcfs, according to Turner.
The Little Goose spill target is 26 kcfs,
which the Corps nearly hit June 5 and 6 when TDG levels fell within gas-cap
levels. TDG in the tailwater hit 127 percent May 27 when the river was spilling
81 kcfs. The downstream forebay at Lower Monumental Dam hit 127 percent the
“LoMo is in transition,” Turner said, noting
that the Lower Monumental Dam spill target has yet to be hit, but TDG levels
were within the gas cap June 6. Tailwater TDG a LoMo hit 128 percent May 23 and
the downstream forebay at Ice Harbor Dam hit 123 percent May 28 and 29.
Ice Harbor Dam, the lower dam on the Snake
River, has for the most part met its spill target of 80 kcfs since June 3, but
the forebay at the next downstream dam, McNary, on the Columbia River continues
to exceed the 115 percent TDG cap. TDG at Ice Harbor’s tailwater hit 130
percent May 27 and the forebay at McNary hit 125 percent May 23 and 24.
Flow at The Dalles Dam on June 3 was about 350
kcfs. At one point in May, flow exceeded 500 kcfs. The forecast is for a flow
level of about 225 kcfs by July 1.
Although flows are also dropping in the
Columbia River, involuntary spill is continuing and TDG at all four lower
Columbia River dams – McNary, John Day, The Dalles and Bonneville dams –
continue to exceed water quality standards set by the states.
Water supply forecasts remain high with an
April – August forecast at The Dalles Dam of 105,908,000 acre feet, which is
121 percent of the 30-year average (1981 – 2010).
Other water supply forecasts are:
-- Lower Granite Dam on the lower Snake River,
April – July, 23.878 MAF, 120 percent of the 30-year average.
-- Libby Dam on the Kootenai River, April –
August, 7.213 MAF, 122 percent of the 30-year average.
-- Dworshak Dam on the North Fork Clearwater
River, April – July, 2.966 MAF, 122 percent of the 30-year average.
-- Grand Coulee Dam on the upper Columbia
River, April – August, 69.008 MAF, 122 percent of the 30-year average.
-- Albeni Falls Dam on the Pend Oreille River,
April – August, 17,692 MAF, 143 percent of the 30-year average.
--CBB, May 18, 2018, “Court-Ordered Spring
Spill Now Moot As High Columbia/Snake Flows Forcing Involuntary Spill At Dams,”
--CBB, May 4, 2018, “Maintaining Court-Ordered
Spill At Columbia/Snake Dams Without Exceeding Gas Caps Proves Challenging,” http://www.cbbulletin.com/440650.aspx
--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,