High salinity in the Delta can negatively impact beneficial uses of water. In 2023, all objectives were met at compliance stations and the Fall X2 action was in effect.
The Measure
Water management agencies comply with State Water Resources Control Board objectives for salinity in the Delta for D-1641 and US Fish and Wildlife's 2008 Biological Opinion for X2.
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Expectations
Water management agencies comply with State Water Resources Control Board objectives for salinity in the Delta for D-1641 and X2.
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Performance Metrics
- Monthly electrical conductivity (EC), water temperature, and X2 in the Delta, evaluated annually.
**Station P12: Starting the 2020 water year, exceedance may occur at multiple times between April and August of a water year, but no action may be taken due to several factors. Details explained on the State Water Board's website.
X2 in the Delta
The X2 targets for September and October come from the U.S. Fish and Wildlife Service (USFWS) Delta Smelt Biological Opinion Fall X2 Action and California Department of Fish and Wildlife's (CDFW) Incidental Take Permit (ITP) to maintain the low salinity habitat at or less than 80 km from the Golden Gate Bridge in the fall following wet and above normal water years.
Next Data Update: The data below will be regularly updated soon after the beginning of the water year in wet and above normal water years.
Map of Delta and San Francisco Estuary with kilometer ticks illustrating distance from the Golden Gate Bridge
USFWS Biological Opinions and X2
2019 Biological Opinion**
In 2019, the USFWS released an updated Biological Opinion on the operation of the CVP and SWP that modified X2 to 80 km or less from the Golden Gate in “above normal” and "wet” years in September and October. The updated Biological Opinion also implemented other measures, such as the operation of the Suisun Marsh Salinity Control Gates and fish food enhancement actions, that are expected to achieve ecological benefits. The previous biological opinion had X2 targets at 80 km or less following above-normal years and 74 km or less for wet years in September and October.
X2 is designed specifically to protect the aquatic life of the Delta estuary. X2 is a physical attribute of the estuary used as a habitat indicator for the location of the low salinity zone. X2 is the location in kilometers from the Golden Gate Bridge where water salinity is 2 ppt (parts per thousand) of isohaline salt. The low salinity zone is where freshwater transitions into brackish water. Historically, the low salinity zone was associated with high primary productivity, zooplankton population, and abundance of native species.
CDFW ITP
In March 2020, CDFW issued an ITP to the Department of Water Resources for long-term operations of the State Water Project. The ITP covers four protected species under the California Endangered Species Act: Delta Smelt, Longfin Smelt, Winter-run Chinook Salmon, and Spring-run Chinook Salmon. The ITP authorization will expire on March 31, 2030, unless renewed.
Future Biological Opinion
A new Biological Opinion has been in progress since 2021. It is expected to be completed in 2024 with the goals of supporting species viability, protecting life history diversity, supporting operational flexibility, providing regulatory certainty, supporting science, monitoring, and creating a single, adaptable, coordinated operation for the Central Valley Project and State Water Project.
Salinity in the Delta is an important water quality characteristic affecting municipal, industrial, agricultural, and fish and wildlife water uses. Changes in Delta salinity have far-reaching impacts, from affecting water supply for farmers in the Central Valley to the wildlife and ecosystems of the San Francisco Bay. When salinity exceeds compliance conditions or changes too rapidly, it can have negative impacts on many beneficial uses of water. This includes altered water taste and availability, crop damage and loss, and limitations for recharging groundwater.
The Delta is a transition zone between freshwater and saltwater, serving as an important habitat for hundreds of native terrestrial and aquatic organisms. The amount of freshwater flowing into and through the Delta drives seasonal and annual salinity levels.
Both natural and man-made actions affect salinity in the Delta and Suisun Marsh. Tidal forces, agricultural run-off, exports, and freshwater inflow from the Sacramento and San Joaquin Rivers jointly influence salinity levels of the Delta. The management of salinity is governed by the Department of Water Resources (DWR) and the U.S. Bureau of Reclamation (USBR) due to their roles in managing reservoirs in the watershed and water exports in the Delta. Since DWR and USBR are water right holders for the State Water Project and Central Valley Project, respectively, they must comply with State Water Board Decision 1641 requirements which help protect water quality in the Delta by setting flow and salinity objectives.
Each chapter of the Delta plan includes strategies to achieve the goals of the plan. These strategies are general guidance on achieving the objective laid out in the plan and in the Delta Reform Act of 2009. Associated with these strategies are recommendations. The recommendations describe more specific and implementable actions to support the achievement of Delta Plan strategies. Strategies and recommendations may also have associated performance measures. Delta Plan performance measures track progress in achieving desired outcomes for the Delta Plan. Below are the strategies and recommendations associated with this performance measure.
Delta Plan Strategy
- Protect beneficial uses by managing salinity
Delta Plan Recommendations
- Refer to Chapter 4's functional flows recommendations
Metric
Monthly electrical conductivity, water temperature, and X2 in the Delta and Suisun Marsh, evaluated annually.
Baseline
Average monthly electrical conductivity, water temperature, and X2 at SWRCB compliance points from 1995 to 2015.
Target
- Water management agencies meet SWRCB salinity objectives for ecosystem purposes at least 99 percent of the time at compliance points
- Water management agencies meet all other SWRCB salinity objectives for urban and agricultural beneficial use at least 99 percent of the time at compliance points
- Water management agencies maintain average X2 for September and October at or less than 74 km in the fall following wet years and at or less than 81 km in the fall following above normal years. The monthly average X2 must be maintained at or seaward of these values for each individual month and not averaged over the two-month period.
Methods
- Delta Compliance reports are available from DWR. These reports point out which stations went over the compliance value and for how long.
- The specific locations and objectives are located in SWRCB's Water Quality Control Plan Appendix K
- Salinity measurements can also be viewed at DWR's CDEC.
Additional Details regarding X2:
*2017 Relaxed Targets
From the USFWS memo: Relaxed targets of the 2008 BiOPs were approved by US Fish and Wildlife Service (USFWS). U.S. Bureau of Reclamation operated its facilities to achieve an average X2 distance of no greater than 80 km instead of the 74 km for October 2017.
From the CDFW memo: California Department of Fish and Wildlife (CDFW) determined that the change to the implementation of the fall X2 Action in October 2017 was not consistent with the California Endangered Species Act. The Department of Water Resources committed to keep X2 at 79 km monthly average for October to significantly minimize any short-term habitat effects to Delta smelt.
USFWS 2017 Memo CDFW 2017 Memo
Data Sources
Delta Compliance
Water Quality Control Plan Appendix K
California Data Exchange Center
Synthesis of studies in the fall low-salinity zone of the San Francisco estuary
Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta.
Isohaline Position as a Habitat Indicator for Estuarine Populations.
An Updated Conceptual Model of Delta Smelt Biology: Our Evolving Understanding of an Estuarine Fish.
A Synthesis of Delta Smelt Habitat in the Upper San Francisco