Lower Deschutes River Water Temperatures Dropping
By Greg McMillan & The Board of Directors of the Deschutes River Alliance It’s mid-July and it’s already been a very hot summer. And a very bad summer for fish. Agencies, anglers and fish advocates are worried about the long-term consequences of large fish kills.
In the upper Columbia Basin, dams are releasing cold water to attempt to cool the Columbia River to try to protect fish. Extra water is being released from dams in Canada, Montana and Washington, according to an article recently posted on Oregon Public Broadcasting’s website.
A coalition of fishing and environmental groups is calling for a blanket closure of all rivers with salmon and steelhead populations if water temperatures exceed 64.4 degrees Fahrenheit (18 degrees Centigrade).
The Oregon Department of Fish and Wildlife, effective July 18, has closed many streams to angling after 2 PM to protect wild fish from heat associated hooking mortality.
Changes in Dam Operations
Back on our own lower Deschutes River, the site of two salmon fish kills, water temperatures are dropping. We would like to acknowledge the release of cold water from Lake Billy Chinook by the dam operators at the Pelton-Round Butte Dam Complex. Portland General Electric and The Confederated Tribes of the Warm Springs Reservation own and operate the dams. This is an important step in an attempt to improve conditions in the lower Deschutes River ecosystem, and possibly provide a cold-water refuge at the mouth of the lower Deschutes for Columbia River migrating fish. The “Deschutes River Near Madras” gauge shown below is located in the tailrace just below the Pelton Reregulation Dam, the last dam of the three dam complex.
Although air temperatures have also been cooler, the cooler dam releases seem to be having an impact at the Moody temperature gauge at the mouth of the Deschutes River.
What Happens When Hot Temperatures Return?
Water temperatures will climb as air temperatures increase. We would like to encourage the dam operators to continue to help mitigate the warm water temperatures in the river with cool water from the bottom of the reservoir, rather than once again warming the river with dam releases. The water temperature at 260 feet of depth in front of Round Butte Dam was 49 degrees on Tuesday, July 14. That is the level at which bottom water is drawn into the Selective Water Withdrawal Tower at Round Butte Dam.
We understand that the dam operators are concerned about depleting the supply of cold water at the bottom of Lake Billy Chinook. Historically, for the 55 years of dam operation prior to implementation of the Selective Water Withdrawal system, this was apparently not a problem. We have studied what happened last year when the dam operators lowered the discharge temperature (the temperature spike in August was due to a lightning strike and subsequent equipment malfunction):
From this graph you can see that it is apparent that the dam operators were able to discharge cool water until the end of September, when decreasing air temperatures cool the river. We would be grateful for that temperature management to be undertaken again this year, when it’s critical for fish survival.
We have had only sporadic reports of single dead fish from guides floating the lower river the past several days. Oregon Department of Fish and Wildlife reports that they found dead spring Chinook, mostly downstream from the confluence of the Warm Springs River with the lower Deschutes. Many of those fish were apparently highly decomposed, which suggests death had occurred several days preceding their observation.
For the Future
We believe that a threshold peak water temperature should be determined so that in the future, when conditions begin to create thermal stress that leads to potentially lethal problems for fish, dam operations would change automatically. Oregon Administrative Rules state that streams with salmon and trout rearing and migration should not exceed a seven-day average maximum temperature of 64.4 degrees Fahrenheit. Discharge temperatures from the Pelton Reregulation Dam did not exceed these temperatures. But river temperatures downstream from the dams did. By discharging colder water using the Selective Water Withdrawal Tower, temperatures downstream from the dams could be proactively and automatically reduced and made safer for fish.
Deschutes River Alliance: Cooler, cleaner H2O for the lower Deschutes River.
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