What can be done to help keep the Bay cool this summer?\u00a0 There are three actions that when taken together and in sequence can help keep the Bay cooler:\u00a0 Keeping the rivers cooler keeps the Delta cooler.\u00a0 Keeping the Delta cooler keeps the Bay cooler.\u00a0 There are also some Bay actions that can sustain cooler water temperatures.<\/p>\r\n\r\n\r\n\r\n
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- Keeping Lower Rivers Cooler<\/strong><\/li>\r\n<\/ol>\r\n\r\n\r\n\r\n
First, how to keep the lower Sacramento and San Joaquin rivers entering the Delta cooler.\u00a0 Higher streamflows speed the water along in the hot Valley keeping the rivers from absorbing heat.\u00a0 We are only talking about 5o<\/sup>F or so, but it is an important five degrees. That is accomplished by maintaining adequate (legally prescribed) streamflows with reservoir releases, especially during summer heat waves that are getting hotter and more frequent with each decade (i.e., climate change).\u00a0<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-7.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 1.\u00a0 Drought year 2022 spring-summer streamflow and water temperatures at Wilkins Slough (RM 120) upstream of the Delta.\u00a0 Red line shows the target of 68\u00baF\/20\u00baC needed to protect fish and keep the Delta cool.<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-6.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 2.\u00a0 Wet year 2023 spring-summer streamflow and water temperatures at Wilkins Slough (RM 120) upstream of the Delta.\u00a0 Red line shows the target of 68\u00baF\/20\u00baC needed to protect fish and keep the Delta cool.<\/p>\r\n\r\n\r\n\r\n
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- The Sacramento River in the North Delta<\/strong><\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n
Next is the Sacramento River channel in the north Delta\u2019s Freeport to Emmaton reach, with Rio Vista in the center.\u00a0 This reach tends to emulate the input at Freeport, although it tends to warm when flow falls below 20,000 cfs (the inflow from Freeport, Cache Slough, and the San Joaquin River), as it too tends to warm as it slows down and sloshes back and forth with the tides in the summer sun.\u00a0 Delta diversions[1]<\/a> can (and often do) take 12,000-13,000 cfs out of the 20,000 cfs Delta inflow (65% is the prescribed limit).<\/p>\r\n\r\n\r\n\r\n
Input water temperatures at Freeport in June of 2023 and 2024, with streamflow of 15,000 cfs, were generally 70o<\/sup>F or higher (Figure 3).\u00a0 In 2023, inflows of 20,000-40,000 cfs brought water temperatures in the 62-66o<\/sup>F range with slightly higher water temperatures during heat waves.\u00a0 When streamflow at Freeport fell below 20,000 cfs in summer 2023, water temperatures reached 70o<\/sup>F or higher, especially during heat waves, when water temperatures spiked 2-4o<\/sup>F.\u00a0 Maintaining 20,000 cfs inflow at Freeport generally would bring water temperatures below 70o<\/sup>F.[2]<\/a><\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-5.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 3.\u00a0 Wet year 2023 and above normal year 2024 spring-summer streamflow and water temperatures of the Sacramento River at Freeport (RM 90) at entrance to the Delta.\u00a0<\/p>\r\n\r\n\r\n\r\n
Downstream of Freeport in the central portion of the Sacramento River north-Delta channel at Rio Vista Bridge, water temperature patterns are similar to Freeport although slightly warmer and more erratic (Figures 4 and 5).\u00a0 Rio Vista is subject to inputs of warmer water from Cache Slough and the San Joaquin River and thus tends to be slightly warmer than Freeport.\u00a0 Net river flows at Rio Vista are also lower, as Delta water diversions can markedly reduce the Delta inflows by this location.\u00a0 Operation of the Delta Cross Channel also complicates the flow splits upstream of Rio Vista.\u00a0 Cooler Delta air compared to the Sacramento Valley is also a factor.\u00a0 However, the main factors appear to be water temperatures and inflows from upstream (Freeport).\u00a0 Keeping Freeport streamflows cooler should keep Rio Vista water cooler, especially during summer heat waves like the three in July 2023.<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-4.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 4.\u00a0 Water temperatures at the Rio Vista Bridge in the north Delta 2019-2024.\u00a0 Red line is recommended 72\u00baF limit.<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/Figure-updated-1024x745.png\")
<\/p>\r\n\r\n\r\n\r\nFigure 5. Water temperature (daily average) at Rio Vista Bridge in north Delta from May-October 2023 \u2013 a wet year. Also shown is Rio Vista Bridge daily average air temperatures.<\/p>\r\n\r\n\r\n\r\n
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- The Bay<\/strong><\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n
Summer Bay water temperatures are a function of inputs from the Delta and ocean, and of local air temperatures and tidal circulation.\u00a0 At the Benicia Bridge between the east Bay (Suisun Bay) and the north Bay (San Pablo Bay), the influence of freshwater inflows is not unlike that in the rivers and Delta.\u00a0 In wet years like 2023, high freshwater inflows in June kept salinity and water temperature lower (<20o<\/sup>C\/68o<\/sup>F) (Figure 6).\u00a0 Warm water generally comes in from the Delta, especially during the twice monthly tidal-cycle draining of Delta water into the Bay (Figure 7).\u00a0 A one-foot stage drop from the 500,000-acre Delta into the Bay is 500,000 acre-ft of warm Delta water that over several days can have a measurable effect on the Bay. \u00a0The late June 2024 full super moon is already heating the Bay with warm river and Delta water (Figure 7).\u00a0 A cooler Delta would make for a cooler Bay.<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-8.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 6.\u00a0 Hourly water temperatures and salinity (EC) at Benecia Bridge in west Suisun Bay June 2022-June 2024.\u00a0 Red boxes denote June periods in each year.<\/p>\r\n\r\n\r\n\r\n
![\"\"](\"https:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2024\/07\/image-9.png\")
<\/a><\/figure>\r\n\r\n\r\n\r\nFigure 7.\u00a0 Hourly water temperature (degrees C) and salinity (EC) in east Suisun Bay in late June 2024 after full moon.\u00a0 Note warm fresher water from upstream (Delta) on ebb tides.<\/p>\r\n\r\n\r\n\r\n
Conclusions and Recommendations<\/strong><\/p>\r\n\r\n\r\n\r\n
Poor water conditions in the Sacramento River, Delta, and Bay this summer will have negative effects on salmon, sturgeon, and other native fish populations.\u00a0 Unless there is action to mitigate these effects, the summer fish die-offs that occurred in summers of 2021-2023 in the Bay are likely to occur again this summer.\u00a0 The following actions can reduce these negative effects:<\/p>\r\n\r\n\r\n\r\n
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- Maintain the water quality standard of 68o<\/sup>F (daily-average) in the lower Sacramento River at the Wilkins Slough gage.\u00a0 This will require raising river flow from the planned 4000-5000 cfs level to 6000-8000 cfs level or higher (during heat waves).<\/li>\r\n\r\n\r\n\r\n
- Maintain an average daily Delta freshwater inflow of 20,000 cfs at the Freeport gage.<\/li>\r\n\r\n\r\n\r\n
- Increase the freshwater inflow above 20,000 cfs and\/or reduce Delta water diversions as necessary during heat waves to maintain a daily-average 68o<\/sup>F at the Freeport gage and maximum hourly 72o<\/sup>F at the Rio Vista gage.<\/li>\r\n\r\n\r\n\r\n
- Consider operational changes to the False River weir, Delta Cross Channel gates, and Montezuma Slough gates, which may also help reduce localized adverse effects.<\/li>\r\n<\/ul>\r\n\r\n\r\n
\r\n\r\n\r\n[1]<\/mark> South Delta exports, smaller regional diversions, Delta agriculture, etc.<\/p>\r\n\r\n\r\n\r\n
[2] Based on review and analyses of many years of data at Freeport and other locations.<\/p>\r\n","protected":false},"excerpt":{"rendered":"
Starting with the Strawberry Moon The Strawberry Moon, sometimes called the planting moon, is the June full moon (e.g., June 21, 2024). June is the end the juvenile salmon and sturgeon emigration season from the Central Valley to the Bay.\u00a0 … Continue reading
- Maintain the water quality standard of 68o<\/sup>F (daily-average) in the lower Sacramento River at the Wilkins Slough gage.\u00a0 This will require raising river flow from the planned 4000-5000 cfs level to 6000-8000 cfs level or higher (during heat waves).<\/li>\r\n\r\n\r\n\r\n
- The Bay<\/strong><\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n
- The Sacramento River in the North Delta<\/strong><\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n