San Francisco Bay Hydrodynamics

Project Chief: Jon Burau

This project studies the hydrodynamics of San Francisco Bay and the Sacramento-San Joaquin Delta. The Bay/Delta region is located at the confluence of the Sacramento and San Joaquin Rivers. This region is a geometrically complex network of tidally affected subembayments, channels, and sloughs. The Delta is a critical component of the State and Federal water delivery system, providing the hydraulic connection between surface water supplies in northern California with farms and cities south of the Delta. The Bay and Delta also must function as an ecosystem, providing life support to a broad range of estuarine and fresh water fish species. Over 20 million Californians depend on fresh-water exports from the Delta; over 4.5 million acres of farmland are irrigated by Delta waters; and several endangered or threatened fisheries depend on the Bay and Delta ecosystem. Unfortunately the need to move water through the Delta has increasingly come into conflict with maintaining a healthy ecosystem. For example, populations of a number of pelagic (open-water) fish species have precipitously declined in the last year and water project operations are one of the suspected reasons for these declines.

Water project operations influence the Delta's aquatic environment primarily by altering the flow distributions within the system. Therefore, the influence water project operations have on many of the things people care about (such as: the temperature and salt fields, the base of the food web, resident and migratory fishes) are a direct consequence of the way in which water project operations alter the flow patterns in the Delta. This project conducts studies that specifically assess the influence the water projects have on flow patterns in the Delta. This project not only investigates the influence that reservoir releases, gate operations, barrier placements, and exports have on the Delta, but also places these changes in the context of natural modes of variability such as the tides, unregulated river flows, and meteorological influences. Understanding the relative influence of these natural and anthropogenic influences on flow patterns in the Delta is crucial for managing the transport of fresh water across the Delta, managing water quality distributions (especially salinity), and managing biological resources and ecological function within this system. Management agencies are considering a handful of significant structural and operational changes in the Delta; among them a Through Delta Facility (TDF), revisions in gate operations for the Delta Cross Channel (DCC), modifications to Franks Tract, increasing the pumping capacity of the State Water Project to 8500 cubic feet per second, and installing of new operable barriers in the south Delta. The estimated costs of these proposed modifications are collectively in the billions. This project is directly involved in research associated with each of these proposed modifications and is taking the lead in investigations of the first three.

The objective of this program is to conduct hydrodynamic research in the Bay and Delta and to provide information to our cooperators, the public, and the professional scientific community in the form of data, technical reports, journal articles, and conference presentations.

This project conducts hydrodynamic transport investigations, in collaboration with a broad coalition of state and federal agencies (DWR, SWRCB, DFG, USBR, and USFWS), by using a combination of three components: Delta Flows Monitoring, Process-Based Field studies and Three-dimensional Modeling. The Delta Flows Network provides long-term flow data at 21 stations throughout the Delta; the Process-Based Field Studies make detailed measurements in certain areas of the Bay/Delta to address specific research/management questions; and the Three-Dimensional (3D) Modeling component studies processes that cannot be measured in the field, provides results where field observations are sparse, and predicts system response to proposed physical and operational changes.

SI3D is a fully 3D, transient hydrodynamic model used in the San Francisco Bay/Delta and elsewhere. The development of the 3D code is ongoing and both the hydrodynamic and particle-tracking models continue to be refined and revised as necessary. The model is used to investigate distributions of the threatened fish species, delta smelt, in the South Delta. This study examines the effects of south Delta pumping on the transport of fish within the delta, defines a ?zone of influence? for the pumps, and seeks ways of minimizing entrainment of fish in the export facilities. This application is critical as the State of California and Federal governments weigh the costs and benefits of changes in exports and operations, and potential modifications to the Frank?s Tract region. Ongoing 3D modeling investigations of low dissolved oxygen conditions in the Stockton Deep Water Ship Channel and of fish entrainment into the Delta Cross Channel are in progress and reports are being written. Evidence of the stature of SI3D in the science community is given by the increasing number of users outside the USGS including: UC Davis, Cornell University, Stanford University, University of Granada (Spain), and Australian researchers. Within the USGS surface-water research discipline, the development of improved capabilities for 3D surface-water modeling has been identified as a top priority.

This project also will continue to develop graphics and visualization software that are generally applicable. The software products from the project are now being used in at least six other USGS science centers and by users outside the USGS.

Process-Based Field Studies: The field studies component has investigated a diverse range of critical issues throughout the Bay and Delta. Detailed field studies are conducted in Suisun Marsh, North Delta, Frank?s Tract, and South Delta. These process-based, interagency and interdisciplinary studies are specifically addressing issues associated with ecosystem integrity and restoration (for example, shallow water habitat regions; tidal and intertidal marsh habitats; and anadromous and resident fish migration and distribution), and human health issues (for example, water quality). Examples of studies include: the Frank?s Tract Studies, investigating the impacts of hydrodyanamics on water quality in the Central and South Delta and fish migration through this complex region; and the South Delta Studies, investigating the impacts of export operations on water quality, water levels, and delta smelt distributions.

Delta Flows: This project began measuring the flows in the Delta in 1987. The network has been expanding since then, and now is comprised of 21 continuously operating flow stations. Plans are to expand the network to 29 stations. These data are used on a daily basis by the water project operators and are used as a framework for understanding how the tidal currents, river inflows, water project exports, temporary barriers, and DCC gate operations impact transport within the upper estuary. These data are also used routinely for numerical model calibration and validation and are regularly leveraged into large interdisciplinary process-based studies. These data have been presented to a wide audience including scientists, managers, and the general public in a number of forums including technical briefings, public forums, scientific conferences, and journal articles.

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