Spill at Detroit Dam began last week, about
three weeks later than normal. The spill is intended to warm the water in the
North Santiam River downstream of Big Cliff Dam, Detroit’s re-regulating dam.
The change is to accelerate both the rate of
emergence of wild spring chinook and winter steelhead fry below the two dams
and upstream passage of adult chinook and steelhead, according to the U.S. Army
Corps of Engineers, which operates the two dams.
Temperature control spill at Detroit began
June 21 to create optimal spawning and rearing conditions of the spring
chinook, listed as threatened under the federal Endangered Species Act, as well
as for threatened Willamette River winter steelhead. Both emergence and adult
migration have been slowed by the colder water released into the river from the
bottom of the dams. Spill adds warmer water to those releases.
As of June 26, some 44 wild spring chinook and
152 winter steelhead have been counted at the Minto Hatchery, operated by the
Oregon Department of Fish and Wildlife and located downstream of the dams.
“We timed the start of the spill operations to
allow the City of Salem time to take water quality samples near Big Cliff Dam
and to process and analyze the data prior to spill flow reaching the intake at
the Geren Island water treatment facility,” said Salina Hart, Chief of the
Corps’ Reservoir Regulation & Water Quality Section. The water treatment
facility is owned by the City of Salem.
Spill at the dam to create a warmer river
downstream normally begins June 1, but the Corps agreed to the delay to allow
the City of Salem enough time to implement and train personnel on new equipment
and treatment options designed to better test and prevent cyanotoxins from
entering Salem’s water treatment facility, according to a Corps press release.
An algal bloom advisory at Detroit Reservoir
that’s been in effect since June 15 was lifted this week, June 25, by the
Oregon Health Authority, according to Corps’ spokesperson Richard Hargrave. He
said that such a bloom is not uncommon this time of year.
Salem has been under some level of water
advisory for much of June, including a week-long “do not drink” advisory for
vulnerable populations, due to cyanotoxins in its drinking water. The
reservoir’s toxic algae bloom is considered a source of the polluted water,
according to a June 25 update from the City of Salem.
The Corps, NOAA Fisheries, Marion County,
along with the cities of Salem and Stayton have been meeting regularly to talk
about mutual operations with regards to public health and the Corps’
responsibilities associated with threatened salmon and steelhead.
Additionally, the Corps has developed a water
quality monitoring plan during the temperature spill operations and will
continue to provide test results to Marion County and the cities of Salem and
Stayton, as well as provide water retention times in the Big Cliff reservoir,
travel time to the City of Salem treatment facility intake, and daily
operational release schedules.
Temperature modeling by the Corps’ water
quality team found that delaying spill beyond June 21 would result in
temperatures that may have “critical impacts” to spring chinook and winter
“We ran several temperature models to look at
the temperature impacts that additional spill delays would have; waiting will
result in critical impacts to fish,” said Greg Taylor, a Corps fisheries
biologist. “The delays we’ve already made have prolonged the time that
steelhead fry emerge from the gravel by five to eight days and delayed chinook
migration in the North Santiam by three weeks.”
Spilling some of the warmer water from Detroit
Reservoir now is a way to preserve colder water for September and October, a
time when water temperatures could exceed limits for spawning and rearing of
chinook salmon, the Corps said. The spill operations do not increase the amount
of water that is regularly released from Detroit Dam on a daily basis.
The target stream temperature downstream of
the dams is a minimum of 50 degrees Fahrenheit and a maximum of 55 degrees F,
Since 2007, a combination of spill and normal
releases of water for hydropower generation from Detroit Dam has been used to
approximate natural pre-dam North Santiam River water temperatures.
At full conservation pool, opening a spillway
gate at Detroit Dam releases warmer water from a depth of about 20 feet below
the surface of the lake, the Corps said. Cooler water from more than 150 feet
below the surface of the reservoir is released when water passes through the
hydropower turbines, allowing the production of electricity. Detroit Reservoir
is nearly full, according to Corps information at http://www.nwd-wc.usace.army.mil/nwp/teacup/willamette/.
In spilling from the spillway and generating
hydropower at Detroit Dam on a daily basis, warm and cold water mixes in the
small pool between Detroit and Big Cliff dams and is continuously released from
Big Cliff Dam to sustain North Santiam River flows within targeted
In the future, the Corps may have another way
to control water temperatures downstream of the dams, while it also aids
juvenile and adult fish passage. Late last year, it said it is considering
adding a $100 to $200 million water temperature control tower in the Detroit
The tower would aid downstream juvenile
passage with attractor flows in the reservoir and it would help control
discharge water temperatures downstream of Detroit and Big Cliff dams and
beyond into the Santiam River system.
The Corps’ Portland District operates a system
of 13 dams and reservoirs in the Willamette River Basin for power generation
and flood control
--CBB, February 23, 2018, “Corps Considers
Mixing Tower At Detroit Dam, Would Be One Of Three In Oregon,” http://www.cbbulletin.com/440264.aspx
--CBB, December 8, 2017, “Corps Seeking Public
Input On Detroit Dam Fish Passage, Temperature Control Scoping Process,” http://www.cbbulletin.com/439923.aspx
-- CBB, June 16, 2017, “Willamette BiOp For
Fish: Four Subbasins Focus Of Corps’ Salmon Reintroduction Programs Above Dams”