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Figure 3: Acoustic Doppler
current profiler (ADCP). |
Technological advances during the 1980s and 1990s have improved our ability to measure water velocity, salinity, and suspended sediment. Acoustic Doppler current profilers (ADCP) can measure vertical profiles of water velocity at 1-meter (or less) intervals every 10 minutes for as long as 3 months (fig. 3 above). The resulting time series of vertical velocity profiles can be analyzed to determine how gravitational circulation changes as salinity and the spring-neap tidal cycle change.
Conductivity-temperature-depth (CTD) sensors can automatically and continuously measure salinity at any location and depth in Suisun Bay for several months. Optical backscattering (OBS) sensors measure the amount of suspended material in the water. Output from these sensors is converted to SSC with calibration curves developed from analyses of water samples (Buchanan and Schoellhamer, 1996). The OBS sensors can be deployed with other instruments to continuously measure time series of SSC. These time series can be analyzed to determine how SSC varies with salinity, freshwater flow, wind, and the spring-neap tidal cycle (Schoellhamer, 1996).
High-quality, long-term data sets from ADCPs, CTDs, and OBS sensors provide the necessary information to better understand the tidal and seasonal variability of salinity intrusion, gravitational circulation, SSC, and entrapment in Suisun Bay. Some results of the analyses of these data are summarized on the next page.
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U.S. Department of the Interior |
U.S. Geological Survey
