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Delta August Adjustment

The State of California has markedly increased inflows to the Delta and reduced exports in early August 2019 (Figure 1). There is no announced reason for this major hydrologic adjustment that has had a major effect on Bay-Delta habitat. The likely reason was to maintain the 14-day average salinity standard of 450 EC at Jersey Point,1 which was exceeded on a daily basis beginning on August 10 (Figure 2).

“Adjustments” to Delta inflow and exports began at the end of July as daily Jersey Point salinity began to exceed the 450 EC standard. The federal Central Valley Project made little or no contribution to this correction.

These recent changes are a textbook example of why the 14-day salinity standard needs to change to a daily standard. State water managers gamed easily controlled parameters, using the 14-day average to squeeze out more exports through July. This operation caused a major system reaction with far-reaching consequences to the State Water Project system and to the Bay and Delta.

The state could have maintained a daily 450 EC limit with gradual small system adjustments and support from the CVP.

Further discussion of the effects follows below.

Figure 1. Sacramento River Delta inflow at Freeport (FPT flow), Delta outflow (DTO resflow), state exports (HRO pumping), and federal exports (TRP pumping), 7/1-8/9, 2019. Note only state exports were affected.

Figure 2. Salinity (EC) at Jersey Point near mouth of San Joaquin River in the Delta 7/14-8/10, 2019.

Delta Inflow
Sacramento River inflow to the Delta at Freeport increased about 3000 cfs to just over 20,000 cfs (Figure 3).  The extra flow came from the Feather River (Oroville Reservoir of the SWP).  The higher inflow coincided with a drop in water temperature at Freeport from 23oC to 21oC.

Delta Outflow
Delta outflow rose about 9000 cfs from near 7000 cfs to 16,000 cfs (3000 from inflow and 6000 from reduced exports, Figure 1).  Outflows rose in the Sacramento channel at Rio Vista (Figure 4) and San Joaquin channel (Figure 5).  Water temperatures also fell about 1oC.

Interior Delta
Flow also increased and water temperature fell in Georgianna Slough (Figure 6).

Suisun Bay
Salinity and water temperature fell in Suisun Bay west of the Delta (Figure 7).

Figure 3. Flow and water temperature in Sacramento River at Freeport 7/1-8/10, 2019.

Figure 4. Flow and water temperature in Sacramento River at Rio Vista, 7/1-8/10, 2019.

Figure 5. Flow and water temperature in San Joaquin River at Jersey Pt, 7/1-8/10, 2019.

Figure 6. Flow and water temperature in Georgianna Slough in the central Delta, 7/1-8/10, 2019.

Figure 7. Salinity and water temperature in Suisun Bay near Pittsburg, 7/1-8/10, 2019.


  1. The standard applies for wet years through August 15.