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Evaluate Alternative Operating Criteria for the Ascending or Descending Limb of the Hydrograph During Real-time Operations

COA 10.18.3 In Agency Review Planning

Focal Species

Winter-run Chinook salmon Spring-run Chinook salmon Delta smelt

Operating-criteria evaluation is integrative rather than species-specific: it draws on listed-species responses (winter-run and spring-run Chinook salmon out-migration timing and survival, Delta smelt distribution) synthesized from the covered-species monitoring suite to test how the ascending and descending limbs of the hydrograph drive impact.

Project Effect Links

Far-field. Real-time diversion at the north Delta intakes alters the shape, timing, and rate-of-change of the Sacramento River hydrograph. Differences in impact between the rising (ascending) and falling (descending) limbs — on outmigration cues, routing into the interior Delta, and habitat availability — are the effect this study quantifies so operating criteria can be tuned to minimize take.

Objectives, Research Questions & Hypotheses

By 2030, use aquatic baseline study information to develop and evaluate alternative operating criteria for the ascending and descending limbs of the hydrograph during real-time operations. The study selects an evaluation framework, integrates the joint-operations model (COA 10.21.8), runs candidate operating scenarios, and analyzes biological response to recommend criteria that reduce impact while meeting biological objectives.

  1. Do diversions on the ascending limb of the hydrograph produce measurably different effects on covered-species survival and routing than equivalent diversions on the descending limb?
  2. Which alternative operating criteria, applied by limb, minimize modeled take while satisfying the biological criteria in COAs 11.115–11.117?
  3. Over what range of water-year types do the candidate criteria remain protective, and where do they trade off against water supply?
  • H1: Equivalent-magnitude diversions on the descending limb impose greater incremental impact on outmigrating salmonids than on the ascending limb, owing to altered cueing and reduced transport flow.

Background

Builds on the covered-species monitoring suite (COAs 10.18–10.21) and prior CalSim/DSM2 operations modeling. Pairs with COA 10.21.10, which generates the empirical ascending-vs-descending-limb difference signal this evaluation consumes.

Methods

  • Evaluation Framework Selection
  • Model Integration with COA 10.21.8 Joint Operations Study
  • Operating-Scenario Runs (by limb, across water-year types)
  • Biological-Response Analysis and Criteria Synthesis

Performance Metrics

  • Modeled reach-specific survival under each candidate operating criterion
  • Routing/entrainment probability into the interior and southern Delta by limb
  • Frequency and duration of criteria exceedances by water-year type
  • Water-supply trade-off (delivered volume) per scenario

Data Management

Scenario inputs, model versions, and run outputs are versioned in the DCP operations-modeling repository with provenance back to the contributing baseline studies; analysis notebooks and result tables are archived alongside each Draft/Final Report.

Reporting Requirements

Draft Study Plan and Final Study Plan to CDFW; Draft Report and Final Report, with the Final Report including a proposed set of alternative operational criteria where supported by results.

Agency Review — CDFW 6

4 open 1 addressed 1 resolved

Pinned to: Objectives, Research Questions & Hypotheses

  • C
    CDFW CDFW 2026-03-20 Scope dispute Open

    The objective presupposes that alternative criteria will be developed. Scope should allow for a finding that existing criteria are already protective; do not pre-commit to a change.

Pinned to: Research Questions

  • C
    CDFW CDFW 2026-02-12 Rephrase research question Addressed

    RQ1 conflates "different effects" with "adverse effects." Please rephrase so the question is directional and testable — e.g., specify the survival/routing endpoints and the direction of the hypothesized limb difference.

    • GM
      Greenwood, Marin 2026-03-03

      Rephrased RQ1 to name the survival and routing endpoints explicitly and added H1 stating the expected direction (descending-limb diversions more impactful).

Pinned to: Background

  • C
    CDFW CDFW 2026-05-01 Fix COA cross-reference Resolved

    Background cites the MMRP reference (10.18.2) where the ITP reference (10.18.3) is intended. Please reconcile the cross-reference.

    • GM
      Greenwood, Marin 2026-05-08

      Corrected — both the ITP (10.18.3) and MMRP (10.18.2) numbering are now noted with the discrepancy flagged.

Pinned to: Methods

  • C
    CDFW CDFW 2026-03-20 Model peer-review / documentation Open

    The COA 10.21.8 joint-operations model that this evaluation depends on has not been independently reviewed. Operating-criteria recommendations cannot be accepted until the underlying model is documented and validated.

Pinned to: Performance Metrics

  • C
    CDFW CDFW 2026-02-12 Add / adjust metric Open

    The metric set should report criteria-exceedance frequency AND duration separately by water-year type, not as a single annualized rate. Dry-year exceedances are the operative risk.

Pinned to: Reporting Requirements

  • C
    CDFW CDFW 2026-04-15 Governance / approval Open

    Any proposed alternative operational criteria in the Final Report must be brought to CDFW for written approval before implementation, consistent with COA 11.111.5.

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