PORTLAND, Ore. — Mother Nature can be comforting and calm but this year it seems like she used our first, middle and last name as she scolded (or scalded) us … “Pacific North [emphasis added] West, what in the world were you thinking?!” … for punching our hypothetical little sister (California). Our punishment has been drought, record-breaking temperatures, wildfires and extremely dry conditions throughout the region. Even though the early part of this summer was a scorching hot nightmare, north western Oregon is fortunate to have a consistent flow of water – thanks to the U.S. Army Corps of Engineers’ system of dams and reservoirs in the Willamette Valley.
As of July 13, 2021, water inflow to Corps reservoirs was 1,747 cubic feet per second, whereas water outflow from those same reservoirs was 4,660 cubic feet per second, according to Salina Hart, Portland District Reservoir Regulation and Water Quality Section chief.
“That heat wave would have been extremely detrimental without the augmentation from our reservoirs,” said Hart. “I don’t know where we would have gotten water to support the needs of fish, let alone irrigation or drinking water,” she said. “What will happen in the next 20 years when there’s more demand, less water and potentially limited places to store that water?”
Perhaps our society is too reliant on the extra flow that is only possible during dry months through Corps water management? Without cold water from the deeper part of the reservoirs, Corps water managers wouldn’t have been able to cool down temperatures in Willamette tributaries during the record-setting heat wave in June that had air temperatures hitting 116 degrees in Portland according to climate.gov, nor would the extra volume of water been able to cool the main-stem Willamette temperatures. For instance, Corps water managers were able to reduce the Willamette River temperatures by 0.6 degrees during the first heat wave (from 69.9 to 69.3 degrees) with “pulses” from reservoirs. With that initial experience under their belts, they were able to decrease temperatures even more during the second heat wave in late June, from 75.2 to 71 degrees.
“We were fortunate to have worked with stakeholders and partners this spring to save some water in anticipation of dry conditions,” said Chris Walker, Fisheries Biologist. “This allowed us to manage temperatures during early summer to a certain degree,” he said. “If we hadn’t adapted to the water year, it could have been more detrimental to salmon. Salmon require cool temperatures to survive and cold water from deep in the reservoirs can help us during long, hot summers.”
The city of Salem might be sweating – not only from the heat wave – because it would be getting dangerously close to losing its water supply without Detroit Dam. According to public scoping comments from city officials during a Corps Draft Environmental Impact Statement (page 246) for downstream fish passage at Detroit Dam, the city’s intake for drinking water needs 750 cubic feet per second to operate:
“The intake requires a minimum of 2.5 ft [the City of Salem clarified that this should be 3 ft of head in a later e-mail] of head at its intake structure to function. The filtration system also requires a minimum 2.5 ft [3 ft] of head to provide enough pressure to push water through the sand filters. Based on current channel geometry, the north channel only attains a minimum of 2.5 ft [3 ft] of head with a river flow rate of approximately 750 cfs, as measured at Mehama.”
As of July 13, inflows from the North Santiam River into Detroit Lake were 698 cubic feet per second (outflows from the dam were 2,210 cubic feet per second). The Little North Santiam River was adding 69 cubic feet per second, which would give Salem just enough water. Salem needs the flows to be 767 cubic feet per second to operate its water supply system. But, how long would that last, through this dry summer and its baking temperatures (as of August 24, the combined tributaries were providing 559 cubic feet per second of water)? Lacey Goeres, the City of Salem’s water quality supervisor, says Detroit Lake helps the city meet customer needs.
"The North Santiam River is a dynamic system with regulated flows from stored water behind Detroit Dam, fluctuating and unpredictable unregulated flows from small tributaries and changing sediment deposition, said Goeres. “Regulated flows released from Detroit Dam provide consistent, adequate flows to ensure that the City of Salem is able to meet customer water demands, especially during the hot summer months when demands peak."
That also doesn’t account for any other person, group or entities’ straws in the river. For example, the Oregon Water Resources Department (OWRD) has issued several water rights permits for the N. Santiam River, the two largest entities are the City of Salem (municipal use) and the Santiam Water Control District (irrigation use).
For this year, there's not a lot of impact for users," said Mike McCord, OWRD Northwest Region Manager. "There are multiple variables that could change that in the future." "It's important to remember that water rights holders may not be using all or part of their water right this year, or they may be taking less water out of the system than their water right allows."
The state government issued an executive order directing state agencies to limit water use, July 7. In a news release, Governor Kate Brown encouraged Oregonians to conserve water.
“Through this Executive Order, state government can respond to this growing crisis, lead by example, and show Oregonians that drought is a serious issue—but one that can be managed if we all work together,” said Brown. “Oregon has a strong history of managing and caring for water, but climate change and chronic drought require water conservation and a commitment to working together.”
The Corps has lived up to the Governor’s standards of caring for water this year by working with other federal agencies to conserve water earlier in the season to help with less water later this summer and learning from other dry years. For instance, Corps water managers had worse precipitation than 2015 (another historically bad water year) but managed to keep more water in the system through adaptive management.
However, that was only possible because the U.S. Army Corps of Engineers has the capacity in its reservoirs to conserve 1.59 million of acre-feet of water (one acre-foot equates to about 326,000 gallons, or enough water to cover an acre of land, one foot deep).