PORTLAND, Ore. – The Corps began temperature control spill operations early this morning to change water temperature in the North Santiam River to create optimal spawning and rearing conditions for threatened spring Chinook and winter steelhead.
“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 Reservoir Regulation & Water Quality Section.
Normally, temperature operations using the spillway at Detroit Dam would have commenced on June 1. However, the Corps agreed to delay until June 21 to allow the City of Salem 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.
Last week, the Corps’s water quality team ran temperature modeling that indicated further delay in spill operations for temperature control in the North Santiam River will result in temperatures that may have critical impacts to threatened spring Chinook salmon and winter steelhead.
“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, 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.”
Temperature operations using the spillway are currently the only way to prevent water temperatures in the river downstream of Detroit Dam from exceeding limits for Chinook salmon in the spawning and rearing months of September and October. The spill operations do not increase the amount of water that is regularly released from Detroit Dam on a daily basis.
“It is important to increase temperatures in the summer. If we don’t, water temperatures will be too high in the fall and result in critical impacts to fish,” said Taylor.
Populations of threatened Upper Willamette River spring Chinook and winter steelhead rely on the North Santiam River basin for their spawning and rearing habitat. 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 temperatures. At full conservation pool, opening a spillway gate at Detroit Dam releases warmer water from a depth of approximately 20 feet below the surface of the lake. 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.
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 temperatures.
The Corps, the National Marine Fisheries Service (NMFS), Marion County and the cities of Salem and Stayton have been meeting regularly to talk about mutual operations with regards to public health and the Corps’s 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.
Detroit Dam works together with Big Cliff Dam to also provide flood risk management. Detroit’s other authorized purposes also include hydropower, water quality, water supply, fish and wildlife, navigation, and recreation.
The U.S. Army Corps of Engineers Portland District operates a system of 13 dams and reservoirs in the Willamette River Basin to help protect lives and reduce property damage from floods. The District also works to increase awareness of flood risks and empower the public to take individual actions to reduce their risk.