Continuous water-quality and suspended-sediment transport monitoring in the San Francisco Bay, California, water years 2018–19

The U.S. Geological Survey (USGS) monitors water quality and suspended-sediment transport in the San Francisco Bay (Bay) as part of a multi-agency effort to address estuary management, water supply, and ecological concerns. The San Francisco Bay area is home to millions of people, and the Bay teems with marine and terrestrial flora and fauna. Freshwater mixes with saltwater in the Bay and is subject to riverine influences (floods, droughts, managed reservoir releases, and freshwater diversions) and marine influences (tides, waves, and effects of saltwater). To understand this environment, the USGS, along with its cooperators (see “Acknowledgments” section), has been monitoring the Bay’s waters continuously since 1988. There are several water-quality characteristics that are important to State and Federal resource managers. Salinity, water temperature, and suspended-sediment concentration are some important water-quality properties that are monitored at key locations throughout the Bay. Salinity, which indicates the mixing of fresh and ocean waters in the Bay, is derived from specific conductance measurements. Water temperature, along with salinity, affects the density of water, which controls gravity-driven circulation patterns and stratification in the water column. Turbidity, a measure of light scattered from suspended particles in the water, is used to estimate suspended-sediment concentration. Suspended sediment affects Bay water quality in multiple ways: it attenuates sunlight in the water column, affecting phytoplankton growth; it can deposit on tidal marsh and intertidal mudflats, which can help restore and sustain these habitats as sea level rises; and it can settle in ports and shipping channels, which can necessitate dredging. In addition, suspended sediment often carries adsorbed contaminants as it is transported in the water column, which affects their distribution and concentration in the environment. Excessive concentrations of sediment-adsorbed contaminants in deposits on the bottom of the Bay can affect ecosystem health. External factors, such as tidal currents, waves, and wind, also can affect water quality in the Bay. Tidal currents in the Bay change direction four times daily, and wind direction and intensity typically fluctuate on a daily cycle. Consequently, salinity, water temperature, and suspended-sediment concentration vary spatially and temporally throughout the Bay. Therefore, continuous measurements at multiple locations are needed to monitor these changes. Data collected at eight stations are transmitted in near real-time using cellular telemetry. The purposes of this fact sheet are to (1) provide information about the USGS San Francisco Bay water-quality monitoring network; (2) highlight various applications in which these data can be utilized; and (3) provide internet links to access the resulting continuous water-quality data collected by the USGS.