Click on Home or the logo above to navigate to the main California Fisheries Blog webpage.

Water Projects’ Temporary Urgent Change Petition 3/18/22 Comment on Provision #1 – Spring (April-June) Delta Outflow and Salinity Intrusion

The U.S. Bureau of Reclamation and the California Department of Water Resources (Reclamation and DWR) filed a “Temporary Urgency Change Petition” (TUCP) on March 18, 2020.  If granted, the TUCP reduce Delta outflow requirements.  The proposed averaging requirements in the TUCP pose a problem in addition to the problem of too little overall outflow.

The TUCP states:

Reclamation and DWR are requesting to modify certain terms as the Projects’ storage and inflow may not be sufficient to meet D-1641 requirements and additional operational flexibility of the Projects is needed to support Reclamation and DWR’s priorities, which include: operating the Projects to provide for minimum health and safety supplies (defined as minimum demands of water contractors for domestic supply, fire protection, or sanitation during the year); preserve upstream storage for release later in the summer to control saltwater intrusion into the Sacramento-San Joaquin Delta (Delta); preserve cold water in Shasta Lake and other reservoirs to manage river temperatures for various runs of Chinook salmon and steelhead; maintain protections for State and federally endangered and threatened species and other fish and wildlife resources; and meet other critical water supply needs. (3/18/22 TUCP, p. 1)

The TUCP is requesting reduced Delta outflow requirements for the April 1 through June 30, 2022 period, for the stated primary purpose of preserving storage in Oroville and Folsom reservoirs.   What I term Provision #1 is reduction of outflow requirement from 3-day average of 7,6001 to 14-day average of 4,000 cubic feet per second (cfs).

The requirement in Revised Water Rights Decision 1641 of a 3-day average of 7,600 cfs is meant to keep salt water from encroaching upstream from the Bay into the Delta in drought years like 2021 and 2022.   This helps to protect the beneficial uses in the Delta including fish, fish low-salinity habitat, Delta agriculture, and south Delta water export water quality.  The TUCP’s proposed Delta outflow of 4000 cfs is meant to provide minimum protection in the face of low available water supply (reservoir storage and precipitation).

The overriding problem with the TUCP’s proposed flow reduction is that it does not require enough flow.  Yet, even accepting the need to reduce flow to allow storage of more water in Reclamation and DWR’s reservoirs, the requested change could be modified to better protect beneficial uses.

Under past TUCPs, DWR and Reclamation have used the 14-day averaging window to game operations to skate as closely as possible to the edge of compliance.  This has led to erratic outflows, often below 4000 cfs (Figure 1).  More precise estimates taking into account tides show outflow is lower than intended (Figure 2).  In these circumstances, salinity has increasingly moved up from the Bay into the Delta under such minimum freshwater outflow (Figures 3-6).

I recommend the outflow required be more stable, allowing for only minimal salinity increase over the spring.  A 3-day average of 4,000 cfs measured outflow would provide greater protection of beneficial uses.

Salinity criteria are more easily defined and measured, and more directly related to beneficial uses.  Criteria for Collinsville, Emmaton, Jersey Point, and Old River that have a maximum for a 3-day average or a maximum daily level with a minimum increase over the spring would also be more protective.

Figure 1. Daily Delta outflow estimated from measured Delta hydrology conditions in spring 2014, 2015, and 2021, drought years when previous TUCPs were implemented

Figure 2. Measured Delta outflow into Suisun Bay in spring 2021.

Figure 3. Salinity in eastern Suisun Bay in spring 2021.

igure 4. Salinity in lower end of Sacramento River near Rio Vista in late April 2021.

Figure 5. Salinity and net tidal flow in lower San Joaquin River channel at Jersey Point in spring 2021.

Figure 6. Salinity (EC) and net tidal flow in lower Old River channel in south Delta near Byron in spring 2021.

  1. The normal requirements are stated in Revised Water Rights Decision 1641, Table 3, footnote 10, pp. 185-186.  The April-June requirement in a Critically Dry year is also met if either the daily average or 14-day running average EC (measurement of salinity) at the confluence of the Sacramento and the San Joaquin rivers is less than or equal to 2.64 mmhos/cm (Collinsville station C2).  From May 1 through June 30, if the Sacramento River Index is less than 8.1 million acre-feet, the flows requested in the TUCP would be the same as the required flows under Decision 1641.