Real-Time Management of Water Diversions to Minimize Entrainment Losses of Fishes: Lessons Learned from the Sacramento-San Joaquin Delta (CA)

A better understanding of how the timing and magnitude of water diversions influence fish entrainment can help managers reduce entrainment of fish and any impacts diversions may have on fish populations. In the Sacramento-San Joaquin Delta (CA), two large water diversions export approximately up to 8 x 10⁹ m3 of water/year for municipal and agriculture use from the heart of the one of the largest freshwater estuaries in North America.  Unequivocally, these water diversions have direct and indirect effects on the fishes of the estuary; however, these effects are not of equal magnitude to each fish species nor are they same for any one species on a year-to-year basis. This study shows that the factors that influence the entrainment of key fishes of interest are largely a function of export rate, expressed as a function of reverse river flow. Turbidity and water temperature were also found to have a large influence on entrainment rates. Also, this analysis shows that each species’ vulnerability to entrainment varies in relation to where they spawn in the estuary and migration route selection. Using over two decades of daily entrainment and other physical data, I identified how entrainment risk of key species of interest could be minimized by altering the timing and magnitude of water diversions during critical periods when they are most vulnerable to entrainment. Ultimately, identification of these factors can increase water operation flexibility by allowing higher diversions when species of interest are predicted to have lower entrainment risks.