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Restoring the Lower Snake River

salmon1.massFriday, Oct. 06, 2017

An annual study that looks at salmonid survival through Snake and Columbia river dams for the first time evaluated juvenile fish survival in the Snake River with and without the presence of the four lower dams on the river, as well as the impact on survival if spill is increased, as it may beginning next year.

The Fish Passage Center released a draft of its annual Bonneville Power Administration-funded Comparative Survival Study in late August and is asking for comment from fisheries managers and the public by October 15. The final CSS is scheduled for completion by the end of December.

The study weighs in on two court-ordered issues: a requirement to consider an option for recovering Snake River salmon and steelhead by breaching the four lower Snake River dams and the value of more spill.

The study says that its analysis provides insight into the potential for dam breaching and whether it can play a role in recovering the Snake River spring/summer chinook that are listed under the federal Endangered Species Act.

“The results presented demonstrate the relative sensitivity of survival and long-term return abundance to changes in hydrosystem operations,” the draft CSS says. “Relying on the empirical estimates of life cycle model parameters, and particularly the finding that powerhouse passage is a significant determinant of in-river survival and early ocean survival, we demonstrated that dam breaching and increased spill can benefit population recovery in relative proportion to the productivities and capacities of the populations.”

The analysis predicts that average return abundances and smolt-to-adult returns increase at higher levels of spill and when dams are breached. That is “owing to the empirical finding that survival is higher when powerhouse passage and water transit times are lower.”

The draft study also says that the results are preliminary because the future conditions simulated by the CSS model are speculative and have a strong influence on predicted survival, but also because the passage assumptions after breaching the dams have not been empirically tested.

“The predicted outcomes represent approximations of the relative magnitude of increased survival and return abundance that are predicted relative to expected passage and water transit time values under flow, spill, and breach conditions,” the draft study says.

In a river that still has the four dams in place, the report predicts a 2 to 2.5 fold increase in return abundance when spill is increased beyond levels called for in the latest biological opinion for the federal Columbia/Snake river power system, and up to levels that would result in total dissolved gas levels of 125 percent.

If the lower Snake River dams – Ice Harbor, Lower Monumental, Little Goose and Lower Granite dams – are breached and the remaining four lower Columbia dams – McNary, John Day, The Dalles and Bonneville dams – operate at BiOp spill levels, then the CSS analysis predicts a 2 to 3 fold increase in abundance above that predicted at BiOp spill levels in a river where the four dams remain. If the TDG limit at the Columbia River dams is increased to 125 percent, then the analysis predicts a 4-fold increase in abundance without the Snake River dams.

“This analysis predicts that higher SARs and long-term abundances can be achieved by reducing powerhouse passage and water transit time, both of which are reduced by increasing spill, and reduced further when the lower four Snake River dams are breached,” the draft CSS concludes.

This part of the analysis was triggered by two decisions in U.S. District Court in Portland by Judge Michael H. Simon.

In May 2016 Simon rejected the 2014 biological opinion for salmon and steelhead for the Columbia River hydropower system and ordered a new BiOp be completed by the end of 2017. In addition to sending federal agencies back to the drawing board to redo the BiOp, Simon said that in the National Environmental Policy Act process that was to follow and is currently underway, that the U.S. Army Corps of Engineers should analyze breaching the four lower Snake River dams as a reasonable and prudent alternative to retaining the dams.

In addition, conservation groups, the state of Oregon and the Nez Perce Tribe asked for injunctive relief that resulted in court-ordered earlier spring spill in a January 9 filing, enjoining the BiOp case.
The draft CSS study analyzes both dam breaching and spill from a biological perspective by estimating fish survival benefits of the breaching. It will leave to others to analyze the costs of breaching.

It analyzed four spill levels – BiOp spill; increased spill up to 120 percent TDG in tailraces of the dams; 120 percent TDG spill; and up to 125 percent TDG spill, and three flow levels.

The Independent Scientific Advisory Board will evaluate the study and its methodology.

In Chapter 5 of the draft CSS, it examines the association of SARs to life-cycle productivity for wild spring/summer chinook and steelhead.

“Major population declines of Snake River spring/summer Chinook and steelhead are associated with SARs less than 1 percent, and increased life-cycle productivity has occurred in years that SARs exceeded 2 percent,” it says. “Pre-harvest SARs in the range of 4 percent to 6 percent are associated with historical (pre-FCRPS) productivity for Snake River spring/summer Chinook. Historical levels of productivity for John Day river spring Chinook are associated with pre-harvest SARs in the range of 4 percent to 7 percent.”

The “Comparative Survival Study of PIT-tagged Spring/Summer/Fall Chinook, Summer Steelhead, and Sockeye DRAFT 2017 Annual Report,” can be found at

Comments should be sent by October 15 to Michelle DeHart at

The study’s project leader is the FPC’s DeHart, but the report is compiled by the Comparative Survival Study Oversight Committee and the Fish Passage Center. Contributors include Jerry McCann, Brandon Chockley, Erin Cooper and Bobby Hsu of the FPC; Howard Schaller and Steve Haeseker are from the U.S. Fish and Wildlife Service; Robert Lessard is with the Columbia River InterTribal Fish Commission; Charlie Petrosky is from the Idaho Department of Fish and Game; Eric Tinus, Erick Van Dyke and Adam Storch are from the Oregon Department of Fish and Wildlife; and Dan Rawding is with the Washington Department of Fish and Wildlife.

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