Review of the Proposed Spill Study

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April 19, 2014 Presentation to Council

In response to the Council's request, the ISAB reviewed the spill experiment proposed by the State of Oregon, the Nez Perce Tribe, and others for inclusion in the Council’s Fish and Wildlife Program. This proposal would increase spring spill levels at each mainstem federal Snake and Columbia River hydropower project up to 125% total dissolved gas level in the tailrace of each dam or biological constraints, and then monitor survival effects over ten years compared to the current court-ordered spill program.

The Council asked that the ISAB consider a number of questions. Detailed answers to those questions are provided in the ISAB’s full report. Review materials also available.


Potential Biological or Other Benefits

  • Prospective modeling of the proposed spill test by the CSS team suggests that increasing spill levels up to 125% total dissolved gas may enable smolt-to-adult-return ratios (SARs) to reach the 4% biological goal for steelhead and approach the 4% goal for Chinook.
  • Knowledge gained through experimental spill management could be generalized to inform operations at other dams. 

Potential Biological or Other Risks

  • The spill test may not result in increased SARs as the justification for the proposed test is based on correlative models that do not establish causality.
  • There may be inadequate information gained to justify the cost due to study design limitations and lack of a detailed study and monitoring plan.
  • The spill test could result in unintended consequences, including:
    • greater adverse gas bubble disease (GBD) effects on salmonids, native resident fish and/or aquatic life;
    • increased delay and/or predation of juvenile fish in tailraces;
    • increased fallback and/or passage delays of adult salmon at the dams;
    • difficulty in holding spill levels at desired levels, for example in a low water year;
    • increased spillway erosion problems;
    • possible navigation issues for commercial and juvenile fish transportation barges at dams;
    • possible effect on Federal Columbia River Power System (FCRPS) Biological Opinion (BiOp) operations or smolt transportation actions because increasing spill will reduce the number of fish collected for transportation;
    • future engineering changes to juvenile fish passage at dams could confound results from this spill test.

Additional Issues

  • A detailed study plan needs to be developed by the proponents. The lack of details and lack of synthesis in the material presented leads the ISAB and others to raise questions (see unintended consequences listed above) that might have otherwise been addressed if a comprehensive study plan was developed.
  • The Oregon and Washington water quality standards for total dissolved gas (TDG) would need to be modified with NOAA Fisheries concurring.
  • Regional work and agreement would be needed on:
    • the study design including how long the test should run to provide convincing evidence of an increase in SARs that is due to increased spill;
    • an monitoring and evaluation plan for TDG, biological and physical parameters; and
    • changes to dam-specific spill patterns.

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