San Francisco Bay

The Collapse of Pelagic Fishes in the Upper San Francisco Estuary: El Colapso de los Peces Pelagicos en La Cabecera Del Estuario San Francisco

American Fisheries Society (AFS) | January 9th, 2007

Although the pelagic fish community of the upper San Francisco Estuary historically has shown substantial variability, a recent collapse has captured the attention of res

Although the pelagic fish community of the upper San Francisco Estuary historically has shown substantial variability, a recent collapse has captured the attention of resource managers, scientists, legislators, and the general public. The ecological and management consequences of the decline are most serious for delta smelt (Hypomesus transpacificus), a threatened species whose narrow range overlaps with large water diversions that supply water to over 25 million people. The decline occurred despite recent moderate hydrology, which typically results in at least modest recruitment, and investments of hundreds of millions of dollars in habitat restoration and environmental water allocations to support native fishes. In response to the pelagic fish collapse, an ambitious multi-agency research team has been working since 2005 to evaluate the causes of the decline, which likely include a combination of factors: stock-recruitment effects, a decline in habitat quality, increased mortality rates, and reduced food availability due to invasive species.

The Decline of Striped Bass in the Sacramento-San Joaquin Estuary, California

American Fisheries Society (AFS) | July 1st, 1985

The abundance of young striped bass Morone saxatilis in the Sacramento-San Joaquin Estuary has suffered an unsteady but persistent decline from population levels that wer

The abundance of young striped bass Morone saxatilis in the Sacramento-San Joaquin Estuary has suffered an unsteady but persistent decline from population levels that were high in the middle 1960s. The decline was particularly severe in 1977 and abundance of young striped bass has been low every subsequent year. The adult striped bass population also has fallen during the past 20 years, but the exact period over which the decline occurred and the rate of decline are not clear. The adult population is now about one-quarter of its former size and there is little sign of recovery. We believe the Sacramento-San Joaquin striped bass population and the fishery that it supports are in serious danger. The cause is most likely one or more of four factors. (1) The adult population is now so low that egg production may be inadequate. (2) The plankton food supply of young striped bass in the western Sacramento-San Joaquin Delta and Suisun Bay has been greatly reduced each spring. Diversion of water from the delta for agricultural purposes is a prime suspect for the decrease in food production. (3) Large numbers of young fish are lost by entrainment in water diversions. (4) The population is stressed by toxic substances such as petrochemicals and pesticides. Additional studies are underway to help determine the principal cause(s) of the striped bass decline.

The Definition of Environmental Justice and the Designation of the California Office of Planning and Research as Coordinating Agency for Environmental Justice

State of California | November 18th, 2019

The Delta as Changing Landscapes

University of California, Davis (UC Davis) | July 1st, 2016

What happens at one place in a landscape influences and is influenced by what happens in other places. Consequently, management and restoration that focus on individual p

What happens at one place in a landscape influences and is influenced by what happens in other places. Consequently, management and restoration that focus on individual places may fail to recognize and incorporate interactions across entire landscapes. The science of landscape ecology, which emphasizes the interplay of landscape structure, function, and change at multiple scales, offers a perspective that can integrate the spatial relationships of ecological processes and the functional interconnections of land and water in the Delta. Although the Delta is one of the most studied estuaries in the world, applications of landscape science have been limited. We describe why it is important to incorporate landscape science into management and restoration, emphasizing how Delta landscapes have changed over the past centuries. The land–water linkages of the past have been broken, waterways have been over-connected, and hard boundaries have replaced the gradual and dynamic transitions among landscape patches. The contemporary landscape also has new, novel assemblages of species and stressors that were not there in the past. This historical perspective indicates how knowledge of past landscape functions can contribute to the restoration and management of contemporary landscapes. We illustrate these points with case studies of inundation dynamics and riparian woodlands, and use a third example to describe a landscape approach to restoration. We propose that science that encompasses the multiple, interacting components of functional landscapes in the Delta will foster resilient and enduring restoration and management outcomes that benefit both people and wildlife. We suggest several ways of moving landscape science to the forefront of management and restoration in the Delta.

The Delta on Fast Forward: Thinking Beyond the Next Crisis

CALFED | September 1st, 2016

The Delta Plan: Ensuring a reliable water supply for California, a healthy Delta ecosystem, and a place of enduring value

Delta Stewardship Council (Delta Council) | May 16th, 2013

The Sacramento-San Joaquin River Delta is the grand confluence of California’s waters, the place where the state’s largest rivers merge in a web of channels—and in

The Sacramento-San Joaquin River Delta is the grand confluence of California’s waters, the place where the state’s largest rivers merge in a web of channels—and in a maze of controversy. The Delta is a zone where the wants of a modern society come into collision with each other and with the stubborn limitations of a natural system. In 2009, seeking an end to decades of conflict over water, the Legislature established the Delta Stewardship Council with a mandate to resolve long-standing issues. The first step toward that resolution is the document you have before you, the Delta Plan.

The Delta Pool

State of California | January 2nd, 1961

The demographic decline of a sea lion population followed multi‐decadal sea surface warming

Nature Portfolio (Springer Nature) | June 26th, 2020

The population growth of top predators depends largely on environmental conditions suitable for aggregating sufficient and high‐quality prey. We reconstructe

The population growth of top predators depends largely on environmental conditions suitable for aggregating sufficient and high‐quality prey. We reconstructed numerically the size of a resident population of California sea lions in the Gulf of California during 1978–2019 and its relation with multi‐decadal sea surface temperature anomalies. This is the first multi‐decadal examination of the sea surface temperature of the Gulf of California and of one of its major predators. A three‐decade sustained warming explained the population’s trend accounting for 92% of the variance, including a 65% decline between 1991 and 2019. Long‐term warming conditions started in the late 80s, followed by the population’s decline from 43,834 animals (range 34,080–58,274) in 1991 to only 15,291 (range 11,861–20,316) in 2019. The models suggested a century‐scale optimum sea surface habitat occurring in mildly temperate waters, from 0.18 to 0.39 °C above the 100‐year mean. The mechanistic links of this relation are still untested, but apparent diversification of pelagic fish catches suggests a reduction of high quality prey. We propose this population should be considered vulnerable to any disturbance that could add to the negative effects of the current warm sea surface conditions in the Gulf of California.

The Draft State Water Project Delivery Capability Report 2021

California Department of Water Resources (DWR) | December 31st, 2021

The California Department of Water Resources (DWR) has authority under state law to construct, operate, and maintain the State Water Project (SWP) to manage, store and de

The California Department of Water Resources (DWR) has authority under state law to construct, operate, and maintain the State Water Project (SWP) to manage, store and deliver water for the benefit of the State. This report is intended to provide information about the key factors affecting the operation of the SWP in California, its long-term capability as a source of water for beneficial use, and an estimate of its current delivery capability. This report meets the requirements of Attachment B to the Monterey Plus Settlement Agreement of May 2003. Water provided by the SWP is a major source of the water supplies available to many SWP contractors. SWP contractors consist of 29 public entities that include cities, counties, urban water agencies, and agricultural irrigation districts. SWP contractors’ local/-regional water users have long-term contracts with the DWR for all, or a portion of their water supply needs. Thus, the delivery capability of water from the SWP system is an important component in the water supply planning of its recipients, and ultimately affects the amount of water available for beneficial use in California. The availability of these water supplies may be highly variable. A sequence of relatively wet water years1 may be followed by a varying sequence of dry or critically dry years. Having good and reliable estimates on how much water each contractor will receive each year —- whether it be a wet water year, a critical year, or somewhere in between -- gives contractors a better sense of the degree to which they may need to implement increased conservation measures, or plan for new facilities or back up sources of water to meet their needs. The geography of California and the infrastructure of water transfer from the source areas, located in the Sierra Mountain Range, to areas of demand for water, makes the Sacramento-San Joaquin Delta a key feature of the SWP’s ability to deliver water to its agricultural and urban contractors in the North Bay, the South Bay, California Central Valley, and Southern California. All but five of the 29 SWP contractors receive water deliveries by diversions from the Delta. These water diversions are pumped by either the Harvey O. Banks or Barker Slough pumping plants. DWR and the United States Bureau of Reclamation (USBR), the managing entities of the two statewide systems of water transfer in California, face numerous challenges in the operation of their diversion facilities in the Delta, and are regulated by several state and federal agencies to maintain, and enhance the Delta’s long-term sustainability. Maintaining suitable quality of water flowing in the channels of the Delta for the numerous in-basin beneficial uses, and the protection of endangered and threatened fish species are important factors of concern for the operators of the Delta export diversion facilities. Ongoing regulatory restrictions, such as those aimed at protecting the estuary’s resident and migratory fish species, are major challenges to a reliable and sustainable water delivery capability of both, SWP and the Central Valley Project (CVP) systems. Complications induced by climate change also pose the threat of increased variability in the frequency and magnitude of floods and droughts. The projected sea level rise caused by the increase in average temperature complicate efforts to manage salinity levels in the channels affected by tides. Additionally, higher ocean levels could result in more frequent water quality degradation in the Delta channels requiring additional Delta outflow to maintain water quality objectives. The 2021 Final Main Report (released at the end of March 2022) may include further information on climate change. Previously, the climate change scenario results were only discussed and presented in the Technical Addendum which is not published during the draft phase of the Delivery Capability Report (DCR). Other challenges include continued subsidence of Delta islands, many of which are already below sea level and supported by relatively unstable levee systems. Thus, the threat of a catastrophic levee failure becomes more significant as water pressure increases against the already fragile levees. The analyses in this report factor in all the current regulations governing SWP and CVP operations in the Delta and assumptions about water uses upstream in the Sacramento River and San Joaquin River watersheds. Analyses were conducted that determined the amounts of water that SWP contractors receive and the amounts of water they choose to hold for use in a subsequent year. SWP Delta exports have decreased since 2005, although the bulk of the change occurred between 2005 and 2009 and in 2019. The former reduction is due to the Delta regulations which constrained exports that culminated in the federal Biological Opinions (BiOps) which went into effect in 2008-2009. These BiOps restricted operations of the CVP and SWP diversion pumps. The later reduction is due to two main factors: 1) the amended Coordinated Operation Agreement (COA) with accompanying project operation changes which reduced SWP exports and increased CVP exports, and (2) a more conservative operation of Lake Oroville by the SWP. Many of the same assumptions on SWP operations described in the 2019 Report remains the same in this update for 2021, however, there were a few notable changes. These include the transition from CalSim II to CalSim 3 and CVP and SWP operational refinements. As a result, the differences between the 2019 and 2021 Reports can be attributed primarily to differences in hydrology, spatial and temporal expansion, more explicit groundwater and surface water interaction representation, and operational refinements. The most salient findings in this report are: Under existing conditions, the estimated average annual delivery of Table A water for this 2021 Report is 2,309 thousand acre-feet (TAF)/year, 105 TAF less than the 2,414 TAF/year estimated for the 2019 Report (Table 5-2). The likelihood of existing condition SWP Article 21 deliveries (supplemental deliveries to Table A water) being greater than 20 TAF/year has decreased by 20% relative to the likelihood presented in the 2019 Report (Figure 5-7).

The Economic Value of Carryover Storage in California’s Water Supply System with Limited Hydrologic Foresight

University of California, Davis (UC Davis) | July 1st, 2021

The security and prosperity of California’s economy depend on a large, interconnected and highly engineered water supply system with vast surface and groundwater stora

The security and prosperity of California’s economy depend on a large, interconnected and highly engineered water supply system with vast surface and groundwater storage operated for over-year storage. Substantial public investment is needed to maintain and improve these systems with changing climate risks, increasing demands, and aging infrastructure. Hydro-economic optimization identifies promising opportunities for managing such systems, but scientific and engineering advances are needed to better incorporate hydrologic uncertainty and conjunctive management of streams and aquifers into such models. Over two decades of research the California Value Integrated Network (CALVIN) linear programming hydro-economic model has yielded insights for California’s inter-regional water system on many fronts, including climate change, groundwater sustainability, conjunctive management in southern California, water markets, and reservoir operations in Northern California. Yet there remains unrealized potential to improve the model’s formulation to better represent inter-annual hydrologic variability while concurrently developing reservoir control rules. To address this gap, this study implements linearized quadratic carryover storage value functions on 26 surface reservoirs and linear groundwater storage penalties on 32 groundwater reservoirs to optimize California’s inter-regional water system seasonal and inter-annual operations with limited seasonal foresight. A convex Pareto front tradeoff between total system cost and groundwater overdraft is developed through multi-objective evolutionary optimization of inter-annual carryover storage penalties. Resulting over-year storage valuations span a wide range of nearoptimal reservoir operations, suggesting substantial system flexibility and adaptability when managed in an integrated way. Generalized relationships between carryover capacity, carryover use, and the marginal value of carryover storage are drawn for the multi-reservoir system. When compared to carryover operations based on California’s current simulation model, CalSim-II, the performance of these near-optimal reservoir operations suggests room to improve currently prescribed reservoir control rules, especially in supporting more  sustainable conjunctive management with aquifers. Overall, this study demonstrates the practicability, feasibility, and utility for understanding large-scale integrated multi-reservoir conjunctive use systems using limited foresight with explicit carryover storage values.