California's Bay-Delta estuary is a biologically diverse estuarine ecosystem that plays a central role in the distribution of California's water from the state's wetter northern regions to its southern, arid, and populous cities and agricultural areas. Recently, the Fish and Wildlife Service and the National Marine Fisheries Service required changes (reasonable and prudent alternatives, or RPAs) in water operations and related actions to avoid jeopardizing the continued existence and potential for recovery of threatened species of fish. Those changes have reduced the amount of water available for other uses, and the tensions that resulted have been exacerbated by recent dry years. The complexity of the problem of the decline of the listed species and the difficulty of identifying viable solutions have led to disagreements, including concerns that some of the actions in the RPAs might be ineffective and might cause harm and economic disruptions to water users, and that some of the actions specified in the RPAs to help one or more of the listed species might harm others. In addition, some have suggested that the agencies might be able to meet their legal obligation to protect species with less economic disruptions to other water users. The National Research Council examines the issue in the present volume to conclude that most of the actions proposed by two federal agencies to protect endangered and threatened fish species through water diversions in the California Bay-Delta are "scientifically justified." But less well-supported by scientific analyses is the basis for the specific environmental triggers that would indicate when to reduce the water diversions required by the actions.

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The San Francisco Bay Delta Estuary is a large, complex estuarine ecosystem in California. It has been substantially altered by dikes, levees, channelization, pumps, human development, introduced species, dams on its tributary streams and contaminants. The Delta supplies water from the state's wetter northern regions to the drier southern regions and also serves as habitat for many species, some of which are threatened and endangered. The restoration of water exacerbated tensions over water allocation in recent years, and have led to various attempts to develop comprehensive plans to provide reliable water supplies and to protect the ecosystem. One of these plans is the Bay Delta Conservation Plan (BDCP). The report, A Review of the Use of Science and Adaptive Management in California's Draft Bay Delta Conservation Plan, determines that the plan is incomplete in a number of important areas and takes this opportunity to identify key scientific and structural gaps that, if addressed, could lead to a more successful and comprehensive final BDCP. The plan is missing the type of structure usually associated with current planning methods in which the goals and objectives are specified, alternative measure for achieving the objectives are introduced and analyzed, and a course of action in identified based on analytical optimization of economic, social, and environmental factors. Yet the panel underscores the importance of a credible and a robust BDCP in addressing the various water management problems that beset the Delta. A stronger, more complete, and more scientifically credible BDCP that effectively integrates and utilizes science could indeed pave the way toward the next generation of solutions to California's chronic water problems.

Extensively modified over the last century and a half, California's San Francisco Bay Delta Estuary remains biologically diverse and functions as a central element in California's water supply system. Uncertainties about the future, actions taken under the federal Endangered Species Act (ESA) and companion California statues, and lawsuits have led to conflict concerning the timing and amount of water that can be diverted from the Delta for agriculture, municipal, and industrial purposes and concerning how much water is needed to protect the Delta ecosystem and its component species. Sustainable Water and Environmental Management in the California Bay-Delta focuses on scientific questions, assumptions, and conclusions underlying water-management alternatives and reviews the initial public draft of the Bay Delta Conservation Plan in terms of adequacy of its use of science and adaptive management. In addition, this report identifies the factors that may be contributing to the decline of federally listed species, recommend future water-supple and delivery options that reflect proper consideration of climate change and compatibility with objectives of maintaining a sustainable Bay-Delta ecosystem, advises what degree of restoration of the Delta system is likely to be attainable, and provides metrics that can be used by resource managers to measure progress toward restoration goals.