Science Supports State Board Delta Flows Proceeding

In August, the State Water Resources Control Board, as required by SBX7 1, will provide flow criteria for the Delta ecosystem necessary to protect public trust resources which include fish, wildlife, recreation and scenic enjoyment. The Water Board held a three-day public proceeding in March to inform its development of flow criteria and identified the key issue for the informational proceeding as “what volume, quality, and timing Delta outflows are necessary for the Delta ecosystem under different hydrologic conditions.”

As a member of the Delta Environmental Flows expert group, Delta Stewardship Council Lead Scientist Cliff Dahm provided an overall technical introduction to the proceeding. He explained what flows are-and aren’t-in his presentation and offered suggestions on how flow criteria can be improved:

  1. Environmental flows are more than just volumes of inflows and outflows.

    • Timing, duration, frequency, and rate of change of flows need consideration

    • Scientific basis for setting flow criteria for rivers has advanced substantially

    • Flow criteria for estuaries are especially challenging with tidal, fluvial, and landscape components

  2. Recent flow regimes both harm native species and encourage non-native species.

    • Enhancing variability and complexity across the estuarine landscape supports native species

    • Evidence suggests that flow stabilization harms native species and encourages non-native species

  3. Flow is a major determinant of habitat and transport.

    • Floodplain activation - flows that connect floodplains and channels are beneficial

    • In-Delta net channel flows - dominated by tides but net flows biologically relevant

    • Net Delta outflow - higher seasonal outflows provide variable habitats favorable for native fish communities

  4. Recent Delta environmental flows are insufficient to support native Delta fishes for today’s habitats.

    • Important benefits from adequate winter-spring inflows and outflows to native fish populations are documented

    • Flow and physical habitat interact in many ways but they are not interchangeable

    • Consider habitat restoration and flow requirements jointly

  5. A strong science program and a flexible management regime are essential to improving flow criteria.

    • Current science provides enough insight to act

    • Role of uncertainty - Uncertainty always exists but good science can reduce key uncertainties

    • Managing uncertainty - Adaptive management with emphasis on integration, synthesis, and action

    • Support new science targeted to where better answers are most needed

After the introductory presentations, the public informational proceeding convened five half-day panels. The panel topics were 1) hydrology, 2) pelagic (open water) fish, 3) anadromous fish, 4) other stressors, and 5) hydrodynamics. Dahm participated in a panel discussing other stressors and in response to a State Board member’s request for summary recommendations, he listed these three next steps:

  1. Restore a more normal hydrograph to water entering the Delta

  2. Reduce ammonium loads within the Delta

  3. Get on with large-scale habitat restoration

The Delta flow criteria will be finalized by the Board in August and will then be submitted to the Delta Stewardship Council within 30 days.