Water Unavailability Methodology for the Delta Watershed, 2021-2023
Due to then critically dry conditions in the Sacramento-San Joaquin Delta (Delta) watershed which resulted in insufficient water supplies to meet all water demands, water quality objectives, and flow requirements, the State Water Board developed the Water Unavailability Methodology for the Delta Watershed (Water Unavailability Methodology for short) in May 2021. The Water Unavailability Methodology identified when supply and demand data indicated that water was unavailable for diversion by water right holders at their priorities of right.
The Water Unavailability Methodology was used to support the issuance of curtailment orders to water right holders and claimants in the Delta watershed when warranted by conditions between August 20, 2021 and April 3, 2023, pursuant to an emergency regulation that expired by operation of law on August 14, 2023. To see which water rights and claims were previously curtailed, see the Delta Watershed Curtailment Status List.
The Water Unavailability Methodology improved upon the approach used during the drought years of 2014 and 2015, and was further refined in response to public comments and updated information. Additional refinements may also occur in the future if better data and improved tools become available.
Please see our Frequently Asked Questions for more information regarding water unavailability in the Delta watershed and the related Water Unavailability Methodology.
Announcements
- April 2, 2024 - Beta version of the 1/19/2023 Water Unavailability Methodology for the Delta Watershed released in Python code (see link at the bottom of the Methodology Resources section below), along with Excel Workbook compiling the history of emergency regulation Curtailment Statuses.
- April 3, 2023 – Curtailment and Reporting Orders Rescinded for the Sacramento-San Joaquin Delta Watershed. For more information, please visit the Delta Watershed Curtailment Status List section on the Delta Drought webpage.
Methodology Resources
| Resource (Date Last Updated) | Resource Description | Prior Versions |
|---|---|---|
Summary Report Summary Report Redline Comparison |
The summary report outlines the methods used to develop the tool and describes the data sources, assumptions, and the bases for the assumptions used to develop the methodology. The redline comparison shows changes between the prior and current versions of the summary report. |
06/27/2022 04/19/2022 11/15/2021 09/27/2021 08/20/2021 07/23/2021 06/15/2021 05/12/2021 |
|
Technical Appendix A: Methodology Spreadsheet Description Technical Appendix A Redline Comparison |
The appendix describes the data sources used to develop the methodology, calculation steps used in the analysis, and outputs used to create the visualizations. It is presented as a data dictionary for the Water Unavailability Methodology Spreadsheet (see below). The redline comparison shows changes between the prior and current versions of appendix A. |
06/27/2022 04/19/2022 02/18/2022 11/15/2021 09/27/2021 08/20/2021 07/23/2021 06/15/2021 05/12/2021 |
|
Technical Appendix B: Demand Data Development Process (04/19/2022) |
The appendix describes how user-reported data from 2018 and 2019 was collected and processed for the water demand dataset used in the methodology. |
11/15/2021 09/27/2021 07/23/2021 06/15/2021 05/12/2021 |
|
Appendix C: Summary of Public Comments
(11/15/2021) |
The appendix summarizes the substantive technical, factual, or legal comments that were received prior to the release of the July 23, 2021 version of the summary report. |
07/23/2021 06/15/2021 |
|
Technical Appendix D: Assessment of Water Unavailability Issues Within the Legal Delta Technical Appendix D Redline Comparison |
The appendix provides additional background information used to evaluate water unavailability in the Legal Delta portion of the Delta watershed. The redline comparison shows changes between the prior and current versions of appendix D. |
06/27/2022 09/27/2021 08/20/2021 Redline Comparison 09/27/2021 to 6/27/2022 |
|
Water Unavailability Methodology Spreadsheet (01/31/2023)* |
The spreadsheet contains the supply and demand datasets and analyses used to implement the methodology and create the visualizations. *The Water Unavailability Methodology is run frequently in order to determine curtailments based on the most up-to-date water supply forecasts. To obtain a copy of the spreadsheet supporting current curtailments or for a specific date, please send an email to Bay-Delta@waterboards.ca.gov with ‘Request for Water Unavailability Methodology Spreadsheet’ in the subject line. |
01/19/2023 06/27/2022 04/19/2022 02/18/2022 11/23/2021 11/18/2021 11/15/2021 09/27/2021 08/20/2021 07/23/2021 06/16/2021 05/12/2021 |
Public Comments
State Water Board staff held several workshops to receive public input on the Water Unavailability Methodology between May 2021 and March 2023. Staff also received and reviewed numerous written public comments, which informed subsequent updates to the Methodology.
To request a copy of written public comments on the Water Unavailability Methodology for the Delta Watershed, please send an email to Bay-Delta@waterboards.ca.gov.
Previous Events
- March 10, 2023 – Staff Workshop on Potential Legal Delta and Return Flow Water Supply Refinements to the Water Unavailability Methodology for the Delta Watershed (Notice | Presentation Slides | Video)
- Technical Document: Water Unavailability Methodology for the Delta Watershed: Possible Legal Delta Supply Adjustments (February 24, 2023)
- Technical Document: Water Unavailability Methodology for the Delta Watershed: Return Flows (February 24, 2023)
- Technical Document: Updated Water Unavailability Methodology Spreadsheet with Possible Legal Delta Supply Adjustments (February 24, 2023)
- November 9, 2022 – Staff Workshop on Proposed Refined Watershed Analysis and Friant Priority Date Adjustments in the Water Unavailability Methodology for the Delta Watershed (Notice | Presentation Slides | Video)
- Technical Document: Water Unavailability Methodology for the Delta Watershed: Refined Watershed Analysis (October 11, 2022)
- Technical Document: Water Unavailability Methodology Spreadsheet with Refined Watershed Analysis (October 11, 2022)
- Technical Document: Updated Water Unavailability Methodology Spreadsheet with Refined Watershed Analysis (November 16, 2022)
- May 12, 2022 – Staff Workshop on Updated Water Unavailability Methodology and Draft Emergency Regulation for the Delta Watershed (Notice | Presentation Slides | Video)
- October 20, 2021 - Staff Workshop on Potential Changes to the Water Unavailability Methodology (Notice | Presentation Slides | Video)
- June 1, 2021 – Board Meeting Informational Item: Update on Water Unavailability Methodology (Video)
- May 21, 2021 – Staff Workshop on Water Unavailability Methodology (Notice | Video)
How to Report an Unauthorized Diversion
The State Water Board relies on the public to help identify unauthorized diversions, diversions by junior water right holders that impact senior water right holders, diversions in violation of permit and license conditions, diversions that constitute the waste or unreasonable use of water, and diversions that cause adverse impacts to public trust resources, such as fish and wildlife.
If you have information that an unauthorized diversion may be occurring, you can submit a complaint through the CalEPA Environmental Complaint website.
Please visit the Complaints Program webpage for more information on water rights enforcement complaints.
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