SF Bayweb 2009: Planting the seeds of an observing system in the San Francisco Bay

A pilot project was recently completed in the San Francisco Bay from May 1-10, 2009, to test the use of advanced moorings combined with undersea and wireless networking for displaying real-time environmental data online. The project was a collaboration among several universities and state and federal agencies and was hosted by SFSU´s Romberg Tiburon Center (RTC) in Tiburon, CA. Two current profilers housed in hydrodynamic moorings were deployed near Angel Island to observe currents throughout the water column and transmit data to shore in real time via a communications gateway mounted on a US Coast Guard navigation buoy. The network was an implementation of the most recent version of the Seaweb system developed at the SPAWAR systems center in San Diego, CA. A series of undersea repeater nodes were used to transmit the signals from the sensors to the buoy using very low power outputs. Shipboard CTD and ADCP surveys were also completed to help understand the observed circulation. The long-term plan is to make these data available all the time at several key choke points within the bay and use it to constrain a new community model of the San Francisco Bay circulation being developed by UC Berkeley and Stanford University. The model output will in turn be used to address community needs in the areas for maritime safety, water quality, spill containment and mitigation, and ecosystem health. Instruments were deployed in Raccoon Strait and the Main Channel on May 1, 2009 and collected data for 10 days. The primary mooring structure was a new package developed at the Naval Postgraduate School that integrated current sensors, acoustic release, and acoustic modems into a Flotation Technologies Stablemoor moored 3 m off the ocean floor. This package allowed for the possibility of migrating sand waves about 2 m high, which could potentially prevent a bottom package from being recovered. Mooring performance was good, with a variance in pitch and roll of only about plus or minus- 5 degrees in very high currents. Observed currents in the Main Channel were predominantly tidal and oscillated from the southwest to northeast at speeds exceeding 100 cm/s. Currents were barotropic over most of the tidal cycle but exhibited an unusual shear in the v-component for about 3 hours at the beginning of each ebb tide. Such shear in the water column is of interest to deep-draft vessels transiting the area. The Raccoon Strait observations were hampered by a failed compass in the instrument: It may be possible to reconstruct the record using the observed speed and the highly oscillatory nature of the flow. Plans are underway for a second, longer deployment in the bay during July 2009. These technologies can potentially allow for obtaining real-time current observations in difficult environments where they were not previously possible.