Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta, San Francisco Bay Delta Action Plan Implementation Support, FINAL REPORT

This report evaluates the cost and utility of adding coupled surface and near-bottom salinity monitors along the axis of the San Francisco Estuary, and the types of equipment and approximate costs of this additional monitoring effort. Expanding the monitoring network by adding downstream monitoring stations, adding stations at depth, and increasing the resolution of monitoring stations along the axis of the estuary will generate data that capture tidal dynamics and may be used to derive equations that predict salinity and other hydrodynamic endpoints with greater precision than currently possible. The proposed monitoring is expected to enhance the hydrodynamic modeling of the salt field and the accuracy of compliance and prediction methods in the estuary.

Springtime outflows through the San Francisco Estuary are managed through the position of the 2 parts per thousand bottom salinity isohaline (X2) along the center-line of the estuary, measured in kilometers relative to the Golden Gate Bridge. X2 is calculated from surface salinity measurements with a constant vertical conversion factor. The current framework of sampling stations does not collect near-bottom salinity along the estuary center-line, does not extend far enough down-estuary to adequately characterize X2 during high flows, and the separation of monitoring locations limits the precision with which the position of X2 can be calculated.

Near-surface and near-bed salinity and turbidity sensors and ancillary hardware could be added to the estuary for an estimated cost of ~ $780K in capital costs and $500K/yr in operation, maintenance, and data processing costs based on a proposed addition to an existing surface salinity network in San Francisco Estuary operated by the US Geological Survey. While this document does not recommend a particular plan for implementation, the compiled information provides rough costs for planning considerations. Data collected through a network of this kind could improve precision of compliance methods with the existing Delta outflow standard. With data collected over time, it would support modifications to a new/modified Delta outflow standard, improve our ability to assess the effectiveness of water quality standards, and improve protection of water supply and aquatic life habitat. These data would also improve the salinity modeling capability and accuracy for future predictions and past evaluations. Expanding the monitoring network also provides a platform to connect hydrodynamic and biological measurements which is necessary for integrating biological and hydrodynamic modeling and advancing knowledge of estuarine mechanisms that influence fish population trends. The specific design of a monitoring network and whether or not the improvements can be optimized for their potential outputs was beyond the scope of the present document and needs to be based on a broader discussion among science experts, regulators, and the regulated community.