San Francisco Estuary and Watershed Science

Managing river–floodplain connectivity can be driven by environmental restoration and/or flood-risk objectives, and science programs are essential for informing projects and policies that promote both objectives. California’s Central Valley floodplains have been highly altered as the result of flow regulation, channelization, and levee construction. Much of the remaining floodplain-like habitats are within flood bypasses that are used to manage flood risk. In recent decades, the habitat value of these bypasses for native fishes has received increased attention, and in 2021 a symposium was held to share the results of over 20 years of scientific studies conducted on Central Valley floodplains and flood bypasses. The symposium sought to foster a shared understanding among scientists and managers about the current information on flood bypasses, and the remaining challenges that must be overcome to maximize benefits to native fish while managing trade-offs. This paper summarizes the symposium’s unique synthesis of the state of the science regarding benefits that native fish accrue from accessing flood bypasses, and remaining uncertainties about population-level benefits and risks when fish enter these systems. We describe a case study to demonstrate how restoration can be accomplished within the flood-bypass management context, provide examples of ongoing restoration projects in the Central Valley, and present recommendations for actions needed to manage and restore flood bypasses at a landscape-scale. Our summary identifies the need to develop a long-term vision for managing and restoring flood bypasses and floodplains throughout the valley that includes: quantifying fish population-level effects, identifying necessary funding sources to implement actions at a scale that achieves societal goals, and streamlining regulatory processes. These steps would allow the actions identified in the vision to be implemented in a transparent, consensus-driven, and timely manner.