State of the Network: Long-Term, High-Frequency Flow and Water Quality Data in the San Francisco Estuary, California

Science Center Objects

The San Francisco Bay and Sacramento-San Joaquin Delta form one of the largest estuaries in the United States. Water flow and water quality in the San Francisco Bay-Delta Estuary are important to the economies of both California and the nation. The Bay-Delta system provides water to more than 25 million California residents and vast farmlands, as well as key habitat for birds, fish, and other wildlife. Issues being addressed in the region are frequently discussed in both the local and national news media. Optimal management of water resources requires the strategic collection of relevant and timely data describing flows and water quality.


Map of measurement stations

Map of stations funded by IEP/DWR and maintained by personnel from the USGS California Water Science Center. NOTE: The entire network of USGS stations within the San Francisco Estuary includes other stations supported by additional partners.

The San Francisco Estuary consists of the Sacramento-San Joaquin River Delta (Delta) and the various smaller bays that comprise San Francisco Bay. Because of its long-term importance, both water quantity and quality have been monitored within the estuary for decades. There are now close to 50 USGS real-time stations within the region reporting discharge, water temperature, turbidity, specific conductivity, and other water quality parameters. The data are typically acquired at fifteen-minute intervals and made publicly available by the USGS NWIS online database (

In the collection of data for this project, the USGS California Water Science Center is working with support from many partner agencies. One of those agencies is the California Department of Water Resources (DWR), through the Interagency Ecological Program (IEP). The DWR/IEP-funded flow and water quality network provides high resolution data over a large portion of the San Francisco Estuary.


The project is divided into five tasks:

  1. Continued operation of flow and water-quality stations.
  2. Continued operation of temperature and specific conductivity stations in San Francisco Bay.
  3. Continued measurement of suspended sediment concentration and water temperature at two stations in the Delta.
  4. Continued participation in the Management and Synthesis Team within IEP.
  5. New measurements to investigate feasibility of new flow stations at locations to be determined within the Delta.

Scientific Approach

Side-looking acoustic Doppler velocity meter and water quality sonde

Side-looking acoustic Doppler velocity meter and water quality sonde on slanted rail system in the Sacramento-San Joaquin River Delta.

The project makes heavy use of established USGS procedures for collection of stage (water level), discharge, and water quality data, and for processing this data and making it public via the USGS database.

The flow stations make use of side-looking acoustic Doppler velocimeters and high-accuracy pressure sensors to allow computation of discharge using the Index Velocity Method. Frequent site visits are made to service sensors and continuously improve calibration.

Most of the water quality measurements are made with water quality instruments with different sensors for reporting turbidity, temperature, and salinity. These sensors are cleaned and calibrated frequently per established USGS protocols.

Relevance and Benefits

Water quality and flow in the Delta ultimately has relevance to all Californians. An extensive dataset is required to make sound and optimized management decisions. This work will provide much of that dataset. The data are used regularly, in real-time, for management decisions.

The data are also relevant to issues other than water supply, such as flooding. Due to land subsidence, much of the Delta’s dry land is well below water surface elevations. These lands are generally protected by levees. Many of these levees are old and not built to modern standards which makes the lands vulnerable to flooding.

The work done within this project is relevant to many of the issues such as improved science planning for water, enhancement of monitoring networks, describing how engineering projects influence the water cycle, providing flood-inundation information, and advancing understanding of processes affecting water availability. These efforts are also is also very important ecologically, providing science essential to addressing environmental contamination, animal health, habitat restoration, and climate change.