Operations of the State Water Project and Delta Conveyance Informational Webinar Highlights


State Water Project aerial image

Aerial image of the State Water Project.

The Department of Water Resources (DWR) hosted a series of webinars to provide background information related to preparation of the Draft Environmental Impact Report (EIR) for the proposed Delta Conveyance Project. The first in a series of four webinars was on Operations of the State Water Project (SWP) and Delta conveyance.

To better understand how the proposed Delta Conveyance Project would operate, it’s important to also understand the function and importance of the SWP, including how the SWP develops and delivers water to communities across California - a key component of DWR’s presentation in this webinar. Other presentation topics in the first half of the webinar included the uniqueness of California’s hydrology and how this presents challenges related to water supply and demand.

The second half of the webinar focused on methods to model operations of the proposed Delta Conveyance Project, which will inform the environmental review process, especially for assessment of impacts to water quality and aquatic resources. The presentation also covered the Draft EIR modeling framework, a description and details related to the models used, modeling scenarios and appropriate use of results.


The informational webinars were intended to only discuss methods, not results, so the presentations focused on approaches, methodologies and assumptions being utilized to conduct the ongoing impact analyses in the Draft EIR. Details related to impact findings and specific mitigation measures are still in process as part of the ongoing environmental analysis but will be included in the Draft EIR and future outreach efforts following publication of the document.


As details about the proposed Delta Conveyance Project are collected and shared, it is important to keep in mind the following key pieces of information:


  • The SWP is a vital water delivery system for the entire state, intended to help address some of our unique hydrological challenges
    • The SWP is the backbone of the state's extensive surface water supply delivery system, supplying water to more than 27 million Californians, 750,000 acres of farmland and supporting local water supply resiliency programs. The Delta is the hub of California’s water management system and location of the SWP’s main water infrastructure.
    • The SWP’s primary source of water is runoff from rain and snowmelt in the Sierra Nevada mountains and Central Valley, which eventually moves through the Delta. Water that is not needed for other purposes is diverted from the southern Delta to portions of the Bay Area, Central Coast, San Joaquin Valley and Southern California.
    • The type, timing, location and increasing variability of precipitation in California present several challenges. For example, most of the rain and snow fall in the mountains in the northern and eastern parts of the state but the population centers and greatest demand are in the central, southern and western parts.
    • This is compounded by mismatched seasonal variability between water supply and water demand and increasingly variable annual precipitation totals due to climate change.


  • Annual SWP deliveries vary from year to year due to real-time and projected conditions, including Delta-specific considerations, however, higher priority needs must always be met first
    • The amount of water the SWP can deliver on a yearly basis depends on several factors such as current storage amounts, a conservative estimate of precipitation and forecast runoff, and reservoir releases needed to meet contractual and regulatory obligations. Initial SWP allocations are typically revised during the course of the year as water supply conditions evolve and become more certain.
    • SWP reservoirs capture excess storm flows in the winter and spring and release for delivery in the summer and fall.
    • Freshwater flows through the Delta’s complex system of channels and islands are strongly influenced by SWP/Central Valley Project (CVP) operations. The interaction between saltwater and fresh water is monitored on a daily and monthly basis at water quality monitoring stations throughout the region, which factor into SWP Delta operational considerations.
    • The first priority for water deliveries are in-basin requirements (water quality control plan objectives, existing water contracts, regulatory and endangered species act requirements), and only after these priorities are met is water supply developed for the state and federal water projects.


  • SWP operational considerations in the Delta would remain the same with the proposed Delta Conveyance Project, but the added flexibility with the new diversion facilities would allow for increased capture of large storm flows
    • Water system operations definitions:
      • Excess conditions: the period when the SWP and CVP are developing their supply, including capturing and storing runoff. Under these conditions, releases from upstream reservoirs plus unregulated flow exceed Sacramento Valley in-basin uses, plus exports.
      • Balanced conditions: when the SWP and CVP are actively managing the system and releasing stored water for eventual Delta export. Under these conditions, releases from upstream reservoirs plus unregulated flow approximately equal the water supply needed to meet Sacramento Valley in-basin uses, plus exports.
    • Compliance with Delta water quality requirements would not change with the addition of the Delta Conveyance Project.
    • The same south Delta operating rules for fishery protections would also apply under the Delta Conveyance Project.
    • New operating rules would apply to the proposed north Delta diversion locations for fishery protections.
    • There would be no change to SWP water rights permits (except adding a new point of diversion).
    • There would, however, be increased operational flexibility with the proposed Delta Conveyance Project to provide the SWP with two Delta diversion options (north and south locations), augmenting the ability of the system to capture excess storm flows when available and increasing efficiency in managing to water quality standards during balanced conditions.

  • The Delta Conveyance Project environmental analysis includes a simulation of the proposed project within our intensely integrated water system
    • Models generally attempt to replicate real world conditions through mathematical relationships based on specific inputs, channel configuration, regulations and operational policy, and utilizing recent historical water demand data.
    • Management models (such as those used for the Delta Conveyance Project) include simulation of managers’/operators’ decisions but can only approximate real time operations, which may be partly subjective and may be informed by many different factors, some of which are not incorporated in the models.


  • The modeling for the Delta Conveyance Project considers various scenarios
    • Baseline of existing conditions (2020) and proposed Delta Conveyance Project and alternatives layered onto existing conditions.
    • Baseline of a No Project Alternative (2040) and proposed Delta Conveyance Project and alternatives layered onto the No Project Alternative. The 2040 baseline includes the effects of climate change on precipitation, runoff, evaporation, crop water demands and sea level rise.


  • How to use modeling results
    • Models are not predictive tools and use of absolute values from an alternative and a baseline to evaluate potential impacts is an inappropriate use of model results. Instead, a comparative analysis is undertaken, focusing on the difference in results from two model simulations.
    • Models use statistical measures of flow, storage, diversions and deliveries, and water quality, as metrics to interpret potential project impacts. Statistical measures include:
      • long-term and seasonal average values
      • water year type average monthly values
      • exceedance probability of monthly values


To learn more and stay informed about the Delta Conveyance Project: