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NW Fishletter #374, October 2, 2017

[1] Draft Results From Model Show Benefits With and Without Snake River Dams

This year's draft Comparative Survival Study dives directly into one of the region's most contentious issues, breaching four dams on the lower Snake River.

The CSS biostatisticians simulated salmon population trends under both breached and impounded hydro system conditions, subject to a variety of spill and flow levels.

Dam breaching, along with spill, is hugely controversial in the Northwest, with advocates convinced that it is necessary for the recovery of Snake River salmonids and opponents equally certain dam removal will hurt local economies and regional power supplies.

This is the first time the CSS has ventured into an analysis of dam breaching. The study is an ongoing, long-term study of salmon and steelhead survival, and is part of the BPA-funded Columbia Basin Fish and Wildlife Program. The annual CSS results are used to measure the program's progress towards mitigation for the federal hydro system.

The CSS is produced by the Comparative Survival Study Oversight Committee and the Fish Passage Center under the leadership of Michele DeHart. Oversight committee members are from the Columbia River Inter-Tribal Fish Commission, Idaho Department of Fish and Game, Oregon Department of Fish and Wildlife, U.S. Fish and Wildlife Service and Washington Department of Fish and Wildlife.

The draft 2017 CSS said last year's federal district court decision in National Wildlife Federation v. National Marine Fisheries Service [01-640], which highlighted dam breaching as a potential area of investigation, warranted an initial analysis of the fish survival benefits of dam removal.

On May 4, 2016, the U.S. District Court for the District of Oregon ordered the National Marine Fisheries Service, aka NOAA Fisheries, to prepare an EIS that complies with National Environmental Policy Act (NEPA). A complete EIS, the federal ruling implied, would examine breaching as one the alternatives to avoid jeopardy under the Endangered Species Act.

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Assessing the effects of total dissolved gas (TDG) on salmonids. Credit: FPC

"Although the court is not predetermining any specific aspect of what a compliant NEPA analysis would look like in this case, it may well require consideration of the reasonable alternative of breaching, bypassing, or removing one or more of the four Lower Snake River dams," said Judge Simon's May 4, 2016 order.

"This is an action that NOAA Fisheries and the action agencies have done their utmost to avoid considering for decades," Simon wrote. District Judge James Redden, who was Simon's predecessor, "repeatedly and strenuously encouraged the government to at least study the costs, benefits, and feasibility of such action, to no avail," Simon added.

The draft 2017 CSS analysis acknowledges it is "focused solely" on estimating the fish survival benefits, not costs or feasibility, of breaching the lower four Snake River dams--Ice Harbor, Lower Monumental, Little Goose and Lower Granite.

CSS scientists use a life-cycle model to predict the long-term effects of four experimental spill alternatives on population recovery and then the long-term effects of those spill levels assuming the lower four Snake River dams were breached.

The four spill levels--defined in terms of the limits of total dissolved gas (TDG) produced at each project--analyzed are 1) spill levels according to the regulations consistent with the current BiOp; 2) increase spill up to limits of 120 percent TDG in the tailraces and 115 percent TDG in the forebays; 3) increase spill up to a limit of 120 percent TDG in tailraces and forebays; and 4) increase spill up to a limit of 125 percent TDG in tailraces and forebays.

Each spill level is evaluated at three flow levels (high, average and low flow), resulting in twelve spill scenarios with the four lower Snake River dams in place and twelve scenarios with the four dams breached.

The draft describes the data, methods, model fitting, assumptions and other aspects of the analysis. The Independent Scientific Advisory Board will evaluate these important details as well as the overall modeling and conclusions.

The fish and wildlife program calls for science reviews of the Fish Passage Center's analytical products, including the annual results of the Comparative Survival Study.

Here are some of the CSS simulation results.

"This analysis provides insight into the potential for dam breach to play a role in the recovery of Snake River spring/summer chinook," the draft study says.

The simulation models the Grande Ronde/Imnaha spring/summer Chinook Major Population Group (MPG), which consists of six Snake River populations.

"The results presented demonstrate the relative sensitivity of survival and long-term return abundance to changes in hydro-system operations.

"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 study authors write.

The results estimate smolt-to-adult returns (SARs) in the 4-6 percent range under most breached spill levels, when powerhouse passage is low and water travel time is in the 8-15 day range.

The impounded scenarios, with various levels of spill, estimate 3-5 percent SARs, with powerhouse passage and water travel times almost double the breached values.

The SAR objectives in the Northwest Power and Conservation Council's fish and wildlife program are 2-6 percent.

The study found "that the most significant benefits to in-river survival rates and smolt-to-adult returns occurred at the highest TDG limit spill levels, and that benefits under breached conditions at BiOp spill levels were higher than under impounded conditions at 125 percent spill levels."

Comments on the draft CSS report are due Oct. 15. The final 2017 CSS report is due Dec. 31. -Laura Berg

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NW Fishletter is produced by Energy NewsData.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: Laura Berg
Phone: (206) 285-4848 Fax: (206) 281-8035

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