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Low Delta Outflow Not Keeping Bay Salt Water out of the Delta

Low Delta outflows at the beginning of summer 2021 (Figure 1) are not adequately keeping brackish Bay water out of the west Delta (Figures 2-4). One reason salt is intruding is the high “spring” tides (Figure 5). Another factor is the State Water Board’s Order granting a Temporary Urgency Change Petition (TUCP) to the Department of Water Resources (DWR) and the Bureau of Reclamation. The Order allowed the installation of the False River Barrier in early June that helps force freshwater Delta inflow from the Sacramento and San Joaquin rivers to the south Delta pumping plants. It also allows lower summer Delta outflows and weaker salinity standards in this critical water year. The normal critical summer outflow criteria is a monthly average 4000 cfs. The outflow requirement was reduced to 3000 cfs. The normal salinity standards for a critical dry year are 14-day-average 2.78 EC at Emmaton and 2.2 EC at Jersey Point. The Emmaton compliance point was moved upstream to Three Mile Slough. Even at the upstream compliance point, the criteria limit has been exceeded (see Figure 2).

In the 2014 and 2015 drought years, Delta smelt almost disappeared entirely when the State Water Board granted a series of TUCPs that moved the salinity compliance points in the Delta upstream. Delta smelt have in no sense recovered.1 In the 2021 TUCP, DWR and Reclamation were unable to show the recent distribution of Delta smelt in the Delta: there are too few Delta smelt left to meaningfully count.

Figure 1. Daily average Delta outflow during June 2021.

Figure 2. Salinity (EC, mean daily) at Three Mile Slough near Rio Vista during June 2021.

Figure 3. Salinity (EC) and water temperature (C) in the lower Sacramento River channel near Emmaton during June 2021. Note spring/neap tide effects with warmer, fresher water draining the Delta on neap tides.

Figure 4. Salinity (EC) in the lower San Joaquin River channel near Jersey Point in the west Delta during June 2021.

Figure 5. River stage in the lower Sacramento River channel near Rio Vista in the west Delta during June 2021.

  1. See for example This blog (see the “Smelt” tab to the right) has chronicled the catastrophic decline of Delta smelt since 2015.