Delta Conveyance Project Fisheries Informational Webinar Highlights


Sacramento River Winter-Run Chinook Salmon

Sacramento River winter-run chinook salmon

As planning and environmental review efforts continue to support the Department of Water Resources’ (DWR) determination of whether a single tunnel option to modernize Delta conveyance should be approved, an important component of the environmental review process is to assess environmental resource impacts within the Sacramento-San Joaquin Delta’s (Delta) estuary. The Delta provides habitat important to the survival of many fish and wildlife species, and DWR’s environmental review will evaluate significant impacts to aquatic resources and consider all feasible mitigation measures to reduce potentially significant effects.

To help keep the public and interested stakeholders informed about the progress of environmental review for the Delta Conveyance Project related to potential impacts to aquatic species, DWR hosted an Informational Webinar on Fisheries - one in a series of four webinars to provide background information related to preparation of the Draft Environmental Impact Report (EIR) for the project.

The Fisheries Informational Webinar presentation focused on environmental setting details for sensitive fish species, migration patterns and fish life cycles. The presentation also included a discussion of fish screen considerations, models, and data and analytical methods being used for evaluation of potential impacts related to the proposed Delta Conveyance Project.

As information about the Delta Conveyance Project is collected and shared, it is important to keep in mind these critical aspects of the project:


  • The proposed project is in the early stages of development and assessment
    • During this time, DWR is evaluating and proceeding with appropriate approaches, methodologies and assumptions for each environmental resource, which are being used to conduct the impact analyses in the Draft EIR, currently in progress. 
    • At this initial stage of design and evaluation, proposed project details are subject to refinement and no decisions will be made regarding whether the project or any project alternative should be approved until the conclusion of the environmental review process.


  • The proposed project, which includes a single tunnel and smaller pumping capacity, is substantially different than California WaterFix
    • Modernizing the state’s water delivery infrastructure by pursuing a smaller, single tunnel project through the Delta will protect water supplies from sea-level rise and saltwater intrusion into the Delta, as well as earthquake risk.
    • The smaller facility size may limit impacts on local Delta communities and fish.
    • This strategy will also build water supply resilience for the State Water Project (SWP) that will have benefits across the state.


  • A variety of fish screen options are under consideration
    • Several types of fish screens were considered, including cylindrical tee screens and vertical flat plate screens.
    • Several items were considered when comparing the various fish screen types including structure and footprint details, flow control capabilities, screen cleaning, noise, operations and maintenance, potential effects to aquatic species, supplier information and others.
    • DWR selected cylindrical tee screens for the proposed project because they result in a shorter in-river diversion structure, have better screen cleaning with less operations and maintenance needs, have better flow control over the full range of diversion flows and produce no noise.

  • DWR has identified preliminary operational criteria to initiate analysis of environmental effects on aquatic resources
    • DWR developed the preliminary operational assumptions to try to avoid or reduce effects of the proposed project and alternatives on sensitive fish species. DWR will analyze the potential environmental effects of these operational criteria in the Draft EIR on resources like water quality and aquatic resources. If this analysis finds significant environmental impacts, DWR may modify operational criteria to reduce or avoid impacts.
    • Subsequent permitting efforts under the Endangered Species Act and California Endangered Species Act may further modify the operational criteria to avoid or reduce effects to sensitive species.
    • All proposed and eventual final Delta Conveyance Project operations will be required to meet applicable Delta standards and policies, including current legal requirements such as the Bay-Delta Water Quality Control Plan and State Water Resources Control Board Decision 1641, which includes requirements for water quality and Delta outflow to meet beneficial uses, and export to inflow ratio requirements. The proposed Delta Conveyance Project would also need to follow applicable requirements in the biological opinions and incidental take permit for Long-Term Operations of the Central Valley Project and SWP.
    • The Delta Conveyance Project would operate in coordination with existing south Delta diversions – a concept known as dual conveyance operations. Dual conveyance would enhance operational flexibility. DWR is assuming that during the winter and spring, the SWP would first divert water at the south Delta facilities and divert excess flows in the north Delta at the Delta Conveyance Project diversion facilities only during high flow periods. During the summer and fall, DWR may divert a small amount of water at the Delta Conveyance Project diversion facilities instead of the south Delta to better manage salinity and realize potential carriage water savings (while continuing to meet water quality requirements).
    • DWR’s preliminary operational criteria include:
      • Fish screen approach and sweeping velocity criteria: requirements on how fast diverted water can move into and past the fish screens, respectively. These criteria minimize near-field operational effects on vulnerable fish and rely on criteria set by the fishery agencies.
      • Bypass flows: requirements on the flows remaining in the Sacramento River and bypassing the Delta Conveyance Project diversions. Allowable operations would range from zero diversions during low flow periods, with diversion rates slowly ramping up as Sacramento River flows increase. These requirements protect survival of fish migrating in the intakes reach and through the Delta.
      • Pulse protection: the Delta Conveyance Project proposes inclusion of pulse protections to further reduce diversions for short periods (beyond what is required through the bypass flow requirements). During key winter flow periods, diversions would decrease to low level pumping when larger concentrations (“pulses”) of migrating winter-run Chinook salmon juveniles have historically been shown to move down the Sacramento River.
      • Low level pumping: the lowest identified diversion levels that are intended to limit operations such that they have no, or only minimal effects on aquatic resources. Low level pumping ranges from 0%-6% of Sacramento River flow.

Learn more and stay informed about the Delta Conveyance Project with the resources below: