Drawing down Lower Granite Reservoir during summer heatwaves could be an effective tool to help sockeye salmon and other protected fish by mitigating high water temperatures, according to analysis performed by the Portland-based Fish Passage Center.
But just as it did in a 1992 experiment, a drawdown would also disrupt barge transportation on the lower Snake River, leave some recreational facilities high and dry, and cause some riverside highways and railroad beds to sag and crack.
At the request of the Nez Perce Tribe and the state of Oregon, the center that is funded by Pacific Northwest hydropower ratepayers analyzed the feasibility of lowering the lower Snake River behind Lower Granite Dam from its present elevation of about 733 feet above sea level to as low as 690 feet. Doing so would reduce the surface area exposed to solar radiation, speed the pace of the river and increase the effectiveness of cold water releases from Dworshak Reservoir.
Eric VanDyke, an analyst for the Oregon Department of Fish and Wildlife working on salmon and steelhead passage issues, said last summer’s high water temperatures that wiped out more than 90 percent of the adult Snake River sockeye, an endangered species, are leading salmon managers to seek new tools to help the fish. He said 2014 and 2013 also saw elevated water temperatures that caused problems for sockeye.
“Those problems kind of put us in the space where we are thinking about alternatives and trying to explore reasoned ideas for addressing elevated water temperatures in general and prompted a request to actually analyze what might happen – what-if type scenarios – if we were to try to lower the reservoir at Granite,” he said.
Temperatures in the Snake River have been moderate this year, thanks in part to rain and unseasonably cool weather. On Thursday, the Snake River below Lower Granite Dam was 65 degrees. The U.S. Army Corps of Engineers attempts to keep the river at or below 68 degrees. To do that, it sends cold water from Dworshak Reservoir downstream, where it mixes with the warmer water in the Snake River. Flows leaving Dworshak Dam were reduced because of the recent cool weather.
“This is a good temperature year; nobody is sweating it,” said Paul Wagner with the National Marine Fisheries Service at Portland. “The past few weeks have been cooler, with the result being the temperatures in all of the rivers are substantially cooler.”
Even so, salmon managers expect summer water temperatures in the 70s to be more common as climate change leads to reduced mountain snowpacks, earlier spring runoff and hotter summer days. David Johnson, director of Nez Perce Tribal Fisheries, said there are no immediate plans to request a drawdown. But knowing modeling shows a drawdown would work has value, given that climate scientists predict an upward trend of hot and dry summers.
“If we are starting to see more of those kinds of summers, then I think we are really going to have to rummage around to see what tools we have to ensure those fish can still handle that,” he said. “Knowing that the modeling indicates what it does, is a good thing to have.”
The Fish Passage Center also looked at the possibility of drawing down Dworshak Reservoir farther than the customary 80 feet it is lowered each summer. That would allow more water to be released in July to help sockeye without jeopardizing later releases in September. The study showed lowering the reservoir an additional 5 to 20 feet would slightly reduce the chance of refilling the following spring.
Reducing either reservoir could expose American Indian artifacts that have long been buried. Margaret Filardo, supervisory fisheries biologist at the Fish Passage Center, said the benefits to sockeye have to be weighed against the costs.
“There are ways to address concerns about cultural resources, there are ways to transport commodities and there are ways to extend beaches and boat ramps,” she said. “It all costs money, so it’s a matter of how important meeting a water quality criteria for listed and endangered species is.”
Bruce Henrickson, a spokesman for the corps’ Walla Walla District, said corps officials are aware of the analysis done by the Fish Passage Center but noted it was not addressed or requested by the agency.
Sam Mace of the Save Our Wild Salmon Coalition said if dams are not breached, as her group advocates, reservoir drawdown and similar measures will need to be taken.
“Down the road, it’s very likely to be on the table,” Mace said, “which again begs the question – wouldn’t the region and Clarkston and Lewiston be better served with taking Lower Granite out and being able to utilize that waterfront and be able to restore it and get the best use out of it rather than having seasonal drawdown?”
Representatives from the river shipping system could not be reached for comment.
Contact Eric Barker at email@example.com or at (208) 848-2273. Follow him on Twitter @ezebarker.
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