Tracing salinity through the southern Sacramento-San Joaquin River Delta, California using continuous salinity monitoring, high-speed salinity transects, and ion fingerprinting

Project ID: 23026
Principal Investigator: Grace Windler
Research Topic: Water Quality
Funded Fiscal Years: 2023 and 2024
Keywords: None

Research Question

This project will address the questions: how does salinity mix and disperse through the southern Sacramento-San Joaquin River Delta channels and what are the best strategies for improving water quality there under different environmental conditions? The project will leverage the targeted and comprehensive monitoring efforts currently underway to help develop salinity management practices in an area where water quality is impacted by Reclamation's Central Valley Project and DWR's State Water Project.

Need and Benefit

Water quality, specifically salinity, has been a concern in the interior southern Delta waterways for decades (U.S. Water and Power Resources Service & South Delta Water Agency, 1980; State Water Resources Control Board, 1999; U.S. Bureau of Reclamation, 2011). Water quality objectives for this area are set by California's State Water Resources Control Board (State Water Board) in the Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary, a.k.a. the "Bay-Delta Plan" (State Water Board, 2018). The State Water Board holds Reclamation and DWR partially responsible for meeting those water quality objectives, due to potential operational impacts from the Central Valley Project and State Water Project.

As climate change progresses, California's already drastic shifts between wet and dry conditions are getting stronger. The length and frequency of drought are likely to increase, thus jeopardizing Reclamation's water supply and our ability to provide adequate flows to the Central Valley System, including the Delta. Multi-year droughts, such as the current 2020-2022 drought felt across California, reduce the amount of carry over storage in upstream reservoirs resulting in decreased flow and degraded water quality downstream. Interior southern Delta salinity is highest during periods of low flow, particularly on the San Joaquin River; therefore, southern Delta water quality objectives are most difficult to meet during periods when water supply and the potential for assimilative capacity are low. Additionally, local in-Delta sources of salinity are not well quantified.

This proposal is crucial to identifying point sources of salinity, areas/times of concern, and strategies for addressing the degraded water quality in the southern Delta. Without ion and isotope data to fingerprint salinity sources as proposed here, assimilative capacity will likely be considered the primary path to meeting interior southern Delta salinity objectives via upstream water supply. The Stanislaus River is the last major tributary to the San Joaquin River upstream from the southern Delta. Reclamation operates New Melones Reservoir on the Stanislaus, which is often regarded by stakeholders as a source of dilution flows to improve water quality in the Delta; however, New Melones Reservoir is over allocated and slow to fill, emphasizing the need for alternative salinity management strategies to assimilative capacity.

This project will immediately fill spatial and temporal salinity monitoring gaps in the southern Delta waterways, which will provide Reclamation and DWR with a more complete understanding of how salinity moves through the system under different flow, tidal, or seasonal conditions. This monitoring effort will provide Reclamation and DWR with a way to immediately evaluate how regionally representative the current fixed monitoring stations are of salinity in the southern Delta channels.

The knowledge gained from this monitoring effort will be used to develop strategies for improving salinity management in the southern interior Delta. Reduced salinity during periods of low flow will reduce impacts to fish and wildlife, agricultural, and municipal and industrial beneficial uses in the southern Delta. Additionally, improved salinity management strategies will have the future benefit of reducing the southern Delta's reliance on upstream flow on the San Joaquin River, thus both improving water quality and conserving water supply during multi-year droughts when Californians need it the most. This future benefit of this project fits directly into Reclamation's mission of responsibly managing water supply for public benefit.

Contributing Partners

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Research Products

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Last Updated: 6/22/20