The temperature control devices at Shasta Dam allow water of different temperatures to be pulled from different depths to meet downstream temperature requirements. (Credit: Sacramento River Task Force)

By Scott Hamilton, President, Hamilton Resource Economics 

The operators of the State and Federal water projects are in a very difficult position. They are mandated to meet several important and often conflicting objectives including water supply and environmental enhancement. In trying to operate to meet competing objectives they have two big problems: one is identifying trustworthy science, and the second is sociology.   

Frequently in Delta science, a situation emerges referred to colloquially as “combat science” where the U.S. Bureau of Reclamation receives a study from one group with one agenda presenting one result, and a different group with the same data presenting contradictory results. With few on the Bureau’s staff sufficiently qualified to determine what represents the best available science, the Bureau is left in a quandary.  

The quality of the science employed on Delta issues varies. Errors are too frequent. Use of univariate analyses that omit more relevant covariates, compelling conceptual models not supported by the data, confounding misuse of conventional terminology, and incomplete use of the scientific process — all of these errors have led to the implementation of inappropriate management actions. 

There is much at stake. On one hand is the very survival of species and on the other, jobs and water supplies to support the hopes and dreams of tens of millions of people and one of the largest economies in the world. People are passionate on both sides, and rightly so, but the Bureau is stuck in the middle.  Whatever they do, one side is going to be unhappy. Passion turns into rage and then the litigation begins. But judges are not adept at working through complicated science issues.  

Resource management in the Delta has been somewhat dismal. Despite 30 years of effort and resources, the biological goals identified in the Central Valley Improvement Act have not been met, the condition of numerous listed species continues to worsen, and water supplies are half of what water contractors were promised and paid for. Now, the Bureau has turned to the National Academy of Sciences to help resolve the science issues. The working arm of the National Academies in the National Research Council (NRC) appoints committees to work on the most difficult issues facing the U.S. Government.  

In this case, the panel is made up of 18 scientists, half of whom are from California and the others from across the nation. The Committee is led by Dr. Perter Goodwin, who recently retired as head of the University of Maryland’s Center for Environmental Science. The initial charge for the Committee is very narrow, focused on just a few issues: Old and River flow management to protect salmon and delta smelt from entrainment at water project pumps, Shasta cold water pool management, and management of Delta flows to enhance summer and fall habitat for delta smelt.  

The Shasta cold water issue concerns the management of cold-water releases on the Sacramento River. The Sacramento River has four different runs of salmon that use the river at different times. Salmon, particularly at young life stages, are very sensitive to water temperatures. In large reservoirs, the water settles into layers with the cold water staying low in the reservoir and the warm water near the surface. Shasta Dam is equipped with flumes that allow water to be drawn from different levels of the reservoir. Reservoir managers can draw water simultaneously from different levels to try to meet downstream temperature requirements for salmon, while maximizing the number of days the requirements are met. But in many years, there is simply not enough cold water to meet all the demands.  

Entrainment issues are a little more complicated. Both the state and federal projects have mechanisms to divert fish to salvage facilities before they reach the pumps. But many fish are eaten before they get to the facilities, and the fish diversion facilities themselves are not fully effective. As a result, endangered fish are killed as a result of exporting water from the Delta. The fish agencies restrict pumping during the first half of the year in the hope that fish can better escape the zone of influence of the pumps. This action is effective in reducing entrainment, but, on average, those protections cost around one million-acre feet per year. When the NRC last considered this issue a decade ago, they thought an engineering solution may be possible to reduce entrainment without large water supply impacts. Water contractors have been working on that solution with the next step being the implementation of a demonstration project in the Delta, but lack of funding has hampered progress. 

The summer and fall habitat is one of those combat science issues. On one hand, some scientists think that more outflows expand the area of water with suitable salinity conditions for delta smelt. Others argue that the smelt needs more food in summer and moving the low salinity field downstream to Suisun Bay does not help because food supplies in that area have been depleted since the invasion of the Asian Clam in 1986.  

The NRC Committee met in Sacramento for a briefing on Delta Issues on Jan. 30-31 and toured the Delta on Feb. 1. The long-term operations of the SWP and CVP are being reviewed as part of new biological opinions. The Committee’s perspective on the science will be very helpful.  A report from the Committee Is expected in the fall of 2025.   

Timeline for many of the operational requirements of Shasta Reservoir.  MRDO = minimum required Delta outflow; EC = electrical conductivity; AN = above normal water year type; W = wet water year type.  Source: USBR Long-Term Operation – Initial Alternatives, Appendix L, Shasta Coldwater Pool Management. 2022. 
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