How the Army Corps tries to keep Detroit Lake full without flooding the Willamette River
Heavy rains and snow melt combine to raise the water in Detroit Lake more than 40 feet in five days. Salem Statesman Journal
The U.S. Army Corps of Engineers is one of Oregon’s favorite punching bags, particularly in the Willamette Valley and at Detroit Lake.
The federal agency is loathed by many anglers, sued by environmental groups and often blamed for keeping the reservoir east of Salem too low for summertime recreation.
But this week, the Corps reminded everyone why its system of dams exists: to stop massive floods from destroying Oregon’s largest cities.
There was certainly damage. Evacuations were issued for 464 properties in Lane County. Highways were flooded in Corvallis. There will be expensive impacts to homes, roads and parks, in addition to a number of people needing rescue from high water.
But given the amount of rain and snowmelt, it’s clear it could have been a lot worse, especially here in Salem. Detroit Lake reservoir rose by 45 feet over five days last week, which means its dam prevented a whopping 41 billion gallons of water from roaring into the Santiam and Willamette rivers.
“We hate to see any flood damage or impact to people’s property,” said Erik Petersen, operations manager for the Willamette Valley dams project. “But what we’re about is preventing the massive, catastrophic events that would have occurred had this system not been in place.”
This week's events laid bare one of the toughest questions Oregon is likely to face in a future with a growing population, a warming climate and more demands than ever on water: should Western Oregon risk the danger of floods to store more water?
The importance of Detroit Lake
Take a close look at Detroit Lake, and you’ll see how many different ways it impacts our lives in Salem.
The 11-mile reservoir stores drinking water for Salem and Stayton that is released gradually via the North Santiam River. A scenario without reservoir storage could mean water shortages and curtailment during late summer in Salem, according to a report by the city.
Detroit Lake also provides hydropower and irrigation for at least 800 farms. Most notably, it provides recreation and a major tourist economy in Detroit and the Santiam Canyon.
For decades, the setup has worked fairly well — Salem grew, major floods became rare and agriculture has a dependable source of water.
(The major downside has been the decline of native salmon and steelhead and harm to wildlife in the Santiam and Willamette rivers).
The vast majority of those uses, both now and into the future, favor a full reservoir, especially in summer. Each spring, thousands across Oregon watch Detroit Lake's water level, hoping for a full pool.
Low water becomes increasing issue
The problem is that during the past five years, Detroit Lake has struggled to reach its traditional summertime water level; when it doesn't get there, the local economy takes an estimated $11 million economic hit, according to a study by Oregon State University.
The lake didn't reach “full pool” in 2015, 2016 and barely reached in 2018 before quickly dropping lower than normal. As recently as April 1, it appeared likely that would happen again this year.
The development led many to suggest the Corps should change the way it stores water.
Right now, the Corps follows a rule curve for Detroit Lake that keeps the reservoir almost empty until Feb. 1, when it slowly begins filling. It depends on spring rain to reach its “full pool” and a healthy snowpack to keep it full.
By tweaking the rule curve, or by starting to fill earlier or more quickly, Detroit Lake could have more water at its disposal. In a future of growing populations and a drier climate, demands on water in Oregon are only expected to increase, making the idea appealing.
The Corps hear the idea a lot, said spokesman Tom Conning, and will study it during coming years as they examine how to divvy up Willamette basin water.
With the water level that is 40 feet below normal, many are concerned the lake will not recover in time for the summer tourist season. Wochit
The problem with too much water
What's the problem with the Corps storing a little more water behind the dam? Last week provided a pretty good illustration.
Detroit Lake was way behind, well below its rule curve and in danger of another low-water summer as recently as April 1. Other major reservoirs, including Green Peter and Foster, were also behind.
At the same time, reservoirs in the southern Willamette Valley, such as Dorena, Fern Ridge, Lookout Point and Hills Creek, were right on track or even slightly above normal.
And then came last weekend.
There were hints the system would bring a lot of rain, but it wasn’t until the 24 hours before that forecasters realized the system would bring as much as 4 to 8 inches of rain.
The deluge, combined with melting snow, brought a nearly unprecedented amount of water into the system in April. The Corps was forced to dump water from Dorena Reservoir at a historic level to keep it from overfilling, leading to flooding that prompted more than 400 evacuations along the Row River and Coast Fork Willamette.
On Friday, the Corps opened the floodgates at Fall Creek Reservoir.
Flooding 2012: PHOTOS: Views of Salem flooding in 2012
Meanwhile, reservoirs such as Detroit were able to absorb an astonishing amount of water, buffering what might otherwise have been much worse flooding, especially along the Santiam and Willamette River in Salem.
In other words, having Detroit at such a low level ended up being an awfully fortunate thing.
Taken together, the 13 Willamette Basin dams have been remarkably successful at stopping major floods since they all came online in 1969. Of the 20 highest river levels on the Willamette in Salem, only six have come since 1969. All of the highest water levels were recorded in the 1800s.
The highest recorded crests were in 1891 and 1861, when the river apparently reached 47 feet. To put that in context, during the historic 1996 flood, the Willamette only reached 35 feet in Salem.
At some point, Oregonians in the Willamette Valley will likely weigh in on a simple question: Should we roll the dice with more water behind our dams to provide more economic security to places like Detroit and the Santiam Canyon?
Or, should we keep Detroit Lake at low levels to prioritize the prevention of floods that occur fairly rarely?
“This is an event that we should remember,” Petersen said of this week's rainfall. “We work really hard to balance the tension between all the competing demands on the reservoirs, but ultimately, our mission is to protect people, infrastructure and a way-of-life downstream.
“We take that mission seriously.”
Historic crests on the Willamette River in Salem
(1) 47.00 ft on 12/04/1891
(2) 47.00 ft on 12/04/1861
(3) 45.10 ft on 02/05/1890
(4) 43.30 ft on 01/16/1880
(5) 37.78 ft on 12/23/1964
(6) 35.09 ft on 02/08/1996
(7) 32.32 ft on 01/17/1974
(8) 31.50 ft on 01/15/1901
(9) 31.30 ft on 02/06/1907
(10) 30.60 ft on 01/02/1943
(11) 30.50 ft on 11/25/1909
(12) 30.30 ft on 01/08/1923
(13) 30.23 ft on 01/22/1972
(14) 29.42 ft on 01/21/2012
(15) 29.28 ft on 01/02/1996
(16) 28.75 ft on 12/30/1998
(17) 28.35 ft on 12/30/1945
(18) 27.47 ft on 01/09/1948
(19) 26.87 ft on 04/11/2019
(20) 26.17 ft on 01/20/1953
Zach Urness has been an outdoors reporter, photographer and videographer in Oregon for 11 years. To support his work, subscribe to the Statesman Journal.
Urness is the author of “Best Hikes with Kids: Oregon” and “Hiking Southern Oregon.” He can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on Twitter at @ZachsORoutdoors.